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September 1995
L213
Science with Minibeasts: Snails
Science with
Minibeasts:
Snails
L213
SCHOOL SCIENCE SERVICE
GUIDE L213
September 1995
L213
SCIENCE WITH MINIBEASTS:
SNAILS
CONTENTS
Introduction
All about snails
1.
Types of snails
2.
The shell
3.
Feeding in snails
4.
Snails on the move
5.
Hibernating snails
6.
How do snails breathe ?
7.
A snail's feelings
8.
Snail reproduction
Housing snails
Investigating snails
1.
When are snails active ?
2.
Where do snails live ?
3.
What do snails look like ?
1
1
1
2
5
5
7
8
8
8
9
10
11
12
12
4.
Investigating snail shells
5.
How do snails grow ?
6.
Measuring snails
7.
How do snails eat ?
8.
What do snails eat ?
9.
What eats snails ?
10.
What can snails sense ?
11.
Investigating snails moving
12.
Snails and surfaces
13.
Snail racing and timing
14.
How strong are snails ?
15.
How do snails breathe ?
Reference materials
Topic web
12
13
13
14
14
15
16
17
17
18
18
19
20
Back cover
This guide was originally published by the ILEA Centre for Life Studies. This edition has been revised, brought up to date and reset.
Strictly confidential - circulation
to Members and Associates only
© CLEAPSS 1995
School Science Service
Brunel University
Uxbridge UB8 3PH
Tel: (01895) 251496
Fax: (01895) 814372
24
(organisms with their digestive systems lying above a prominent ‘foot’ on which the animals move). The one most likely to
be found in gardens and around schools is the common snail,
Helix aspersa (Helix: spiral; aspersa: bespangled). This has a mottled brown shell and usually grows to medium size. Common
snails used to be eaten in London quite a lot. They were called
‘wallfish’ because of their habit of ‘swimming’ up walls.
Introduction
Snails are particularly useful organisms for introducing simple
science activities. They are perhaps most effectively used in
primary schools but would find a place in many introductory
science courses in the first years of secondary schools.
They are readily collectable, widely available in the local environment and easy to keep in the classroom or laboratory over
short periods. They are easily handled and allow a wide variety
of experimental and observational studies. Many other activities
may arise out of working with snails. Just some possible routes
of working and related studies are shown in the ‘topic web’ on
the inside of the back cover.
The edible or Roman snail, Helix pomatia, is not found on cultivated land but on open downland and areas of chalk and limestone in Southern England. This snail can measure up to 10 cm
in overall length and 85 g in weight. (This large snail was much
prized for food by the Romans, as it is by the French today. They
were, and still are, fattened on special snail farms. Recently, in
parts of France, so many were captured for food that they became very scarce. Restaurants sometimes served up empty
shells filled with pieces of cooked lung - and no one knew the
difference !).
Work on snails could arise out of the chance event of a pupil
bringing a snail into school, from the acquisition of a new ‘pet’,
eg, a giant African land snail for the animal corner, discussions
on food, eg, edible snails, or pupils can go off on a snail hunt.
Cepaea nemoralis and hortensis, the brown-lipped and whitelipped snails, are generally smaller than the common snail and
found in grassy areas, woodlands and hedgerows. Apart from
the lip (see later), the shell is often yellow but may be shades of
white, pink or brown. There also may be up to five brown or
black bands spiralling round the shell. It is thought that this
variation in coloration helps to camouflage snails when in different environments or habitats, eg, dark shells on brown leaf litter,
cream shells on chalk downland.
All about snails
This section gives basic and background information on snails
that will be helpful for the various activities described later and
will provide support for further project work.
1. TYPES OF SNAILS
An interesting alternative to these British snails is the giant
African land snail, Achatina fulica. As its name implies this can
grow to a large size. [An outsize specimen, "Gee Geronimo",
owned by someone in Hove, weighed 900g (2 lb) and measured
39.3 cm (15.5 inches) from head to tail; shell length 27.3 cm
There are lots of different types of snails that all belong to the
mollusc group (animals with no segments or limbs and usually
a fleshy foot for movement). This group in turn is part of the
larger gastropod (literally ‘stomach foot’) collection of animals
1
(10.75 inches). The snail was collected in Sierra Leone in 1976.] It
is often found in pet shops and is bred around the country in
snail farms as a source of food. (See our guide L197, Giant African land snails, for further details on this animal, including how
to keep it in school and various sources from where it can be
obtained.)
2. THE SHELL
Snails are univalve molluscs, ie, with shells in one piece. (Mussels and oysters have shells with two parts or valves hinged
together and are the bivalves.)
run in a clockwork direction (dextral) in most snails. If you find
an anti-clockwise snail (sinistral coiling), you have a very rare
specimen !
There are lines of growth and fine ridges running across the
whorls. These represent periods in the life of the snail when it
was inactive and so produced thicker bands which, at the time,
would have been at the lip of the mouth of the shell. The thicker
the bands, the longer the period of hibernation in the winter or
inactivity (aestivation) in the summer.
As a young snail grows in size, it also grows its shell, rapidly at
first and then more slowly. New material is laid down at the
mouth of the shell and the shell grows round in a spiral. By the
autumn of the first year there are usually three whorls or coils of
the shell. The snail is normally fully grown by autumn of the
second year and then it has four and a half whorls. The whorls
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Kidney
Heart
Lung
Intestine
Mantle
Breathing hole
Salivary gland
Crop
Eyes
The spiral of the shell if unwound is a cone. This is a good
shape for growing because when material is added to the end,
the whole cone gets bigger but stays the same shape. The snail
stretches out its head and foot from the body whorl - the large
last coil of the shell.
The rest of its body with all the internal organs is twisted and
coiled up to the apex. A layer of skin, the mantle, covers the
inside of the shell and forms a thickened rim at the mouth of the
shell, called the collar. The mantle and collar produce the shell
of the snail.
3
The construction of the shell
There are 3 layers:
(a) A thin horny layer, the peristracum, is on the outside. It is
resistant to acids in the soil.
(b) The middle layer of crystalline calcium carbonate is made by
the collar of the mantle at the shell lip. If it were not for the
horny layer’s protection it would be eaten away by soil acids
especially in young snails with delicate thin shells. This middle
layer is secreted as long as the snail keeps growing.
(c) The inner layer of ‘pearl’ is laid down by the whole surface of
the mantle lining the inner shell wall. It continues growing even
after the snail is adult and so thickens the shell from the inside
and can repair cracks or holes that may arise, eg, from attacks by
birds.
How the snail is anchored in the shell
There is a central pillar, the columella, around which the spiral
shell is coiled. The snail is fixed to the columella by a strong
muscle and cannot be pulled out of its shell without tearing this
muscle and killing the snail. A shell damaged by thrushes is
shown in the diagram opposite.
4
3. FEEDING IN SNAILS
Food is first examined by the short lower tentacles and lobes of
skin around the mouth. If the food is suitable, the snail can feed
in two ways. It can scrape away at the surface of the food with
its tongue or radula - a ribbon with over 14 000 minute saw-like
teeth in the common snail.
4. SNAILS ON THE MOVE
The radula rasps on the food against a horny upper jaw. As the
radula is worn away, it is renewed from behind. It is supported
by a pad of cartilage and muscles move the radula over this.
Snails may also use their horny jaw to bite pieces out of a leaf in
much the same way that caterpillars eat.
In the wild, the snail is only active when it is warm and damp
(after rainfall) and usually when it is dark. The snail glides
smoothly along on its muscular foot. Up to eight waves of contraction can be seen travelling towards the head end of the snail.
The side of the foot can be seen to undulate on some occasions some say that the snail is ‘galloping’ when moving in this fashion.
Snails also make good food for other animals and are regularly
attacked by thrushes, hedgehogs, rats, large beetles and humans
(25 million a year in France). Snails have the same nutritional
quality as lean beef. (The snail-eating record is held by Mr
Thomas Greene of La Plata, Maryland USA. On the 14th July
1981, in Dominique’s Restaurant, he consumed 350 snails in 8
minutes 29 seconds !).
5
A slime gland just behind the mouth releases a constant stream
of slime or mucus over which the snail glides. The rougher the
surface moved over, the more slime that is laid down, as indicated in the table below.
Snails are cold-blooded, which is a confusing term. It means that
they are unable to maintain a constant, warm body temperature,
unlike mammals and birds. They are therefore unable to move
during the winter but will be active when it is warmer. A coldblooded animal always has the same temperature as its surroundings but this means that on a warm day, a cold-blooded
snail actually has very hot blood ! The fastest snails have been
shown to be Helix aspersa.
The world record speed for a snail was recorded in Cougham,
Norfolk on July 17th, 1988. A specimen of Helix aspersa called
"Tracker" completed a 33 cm (13 inches) course in 2 minutes 31
seconds. This works out at 0.0049 miles per hour (0.0079 kilometres per hour or 7.9 metres per hour). Tracker won a silver
tankard stuffed with lettuce leaves !
The snail has some difficulty in moving on powdery surfaces.
Thus new seedlings are sometimes protected from snail attack
by spreading ash or soot around the plant.
6
5. HIBERNATING SNAILS
The world record for the fastest snail pulling a load is another
specimen of Helix aspersa called "Hercules". In the Basque
town of Val de Trapagua in Spain on July 9th, 1988, he/she
dragged a 241 g stone for 47 cm (18.5 inches) in 10 minutes.
If a snail becomes either too cold or too dry, it will become inactive. It recedes far into its shell and produces a waterproof covering across the shell mouth.
Snails respond to gravity by moving upwards. This response is
only very strong if the snails are immersed in water (or rained
on in the wild). If the snail dries out, it is much less likely to start
climbing. Thus snails will climb up plant stems to reach the
leaves but generally only when the conditions are right and the
snail won’t dry up.
When the snail reaches a horizontally-placed leaf, it will usually
stop climbing and come to rest upside down on the lower side
of the leaf. Here it can feed and there is less chance that it can be
detected by predators. The same sort of behaviour is seen when
snails climb up objects other than plants, perhaps to seek places
for shelter.
Snails produce more mucus as they move upwards, presumably
to help them grip onto the surface as they climb. The greater the
slope, the more mucus that is secreted.
This is the epiphragm and is made of hardened slime. In winter
it is much thicker and there may even be more than one
epiphragm produced, rather like double-glazing ! A small porous patch in the epiphragm allows in just enough air for the
inactive snail to survive.
Snails can lie dormant generally for up to a year, losing 30% of
their body mass as water. The record big sleep is 47 years !
7
6. HOW DO SNAILS BREATHE ?
The tentacles
There is a small hole on the right-hand side of the snail which is
partly hidden by the shell lip. The hole leads into a large space the snail's lung - inside the mantle. This
has a moist lining well supplied
with blood vessels; gases are
exchanged between the
air inside the lung and
the snail's blood stream.
The most noticeable sense organs are the two pairs of tentacles
at the head end of the animal. The smaller, lower tentacles are
used to test surfaces for
food by tasting or smelling. (The upper lip
also can detect chemicals in the environment.)
Unlike the blood of
humans and other
mammals which turns
bright red with oxygen, the snail's blood
turns blue.
The tentacles of the
longer, upper pair
have small eyes at
their tips. Sight is rather dim
but sufficient to detect the difference between light and dark
and to register a vague impression of the structure of objects.
Breathing hole
Genital aperture
The four tentacles are hollow and can be withdrawn inside the
head for safety, when the tips are pulled ‘outside in’.
When the snail is retracted
inside its shell, it requires very little
air but its breathing rate increases when
it is warm, moist and active.
8. SNAIL REPRODUCTION
Snails are hermaphrodites, ie, a single animal produces both
eggs and sperm. Eggs are, however, always fertilised by sperm
from another snail. This cross fertilisation is achieved by the
exchange of packets of sperm between two snails.
7. A SNAIL’S FEELINGS
Can you hurt a snail's feelings ? What senses does a snail have ?
The snail is clearly able to detect changes in temperature, moisture, light and food (chemicals) because it reacts to these changing stimuli by moving, hibernating or feeding.
It seems that the whole skin is sensitive to touch and vibrations
but some parts are more sensitive than others.
8
Two mating snails become temporarily joined together by each
shooting a chalky ‘dart’ about 5 mm long into the foot of its
partner. This stimulates jelly-covered sperm packets to be transferred into each snail’s genital opening by the hollow penis tube.
The snails separate, the eggs are fertilised by the stored sperm
and start to develop. Eggs are provided with a food store and an
outer coating to prevent them drying up. Eggs are laid in a
cavity excavated in the soil by the snail, usually between 40 and
100 in total. They develop and hatch normally within 25 days.
As all the necessary information on housing snails is given in
guide L197, only brief details are given here.
Housing snails
Vivarium
The CLEAPSS guide L197 on keeping the giant African land
snail gives basic information which is mostly applicable for
housing snails brought into school from the local environment.
Any plastic or glass aquarium tank. Cover it using Perspex or
glass sheet (with taped edges) but allow for some ventilation.
Habitat
It is not necessary to heat the snails' vivarium as for the giant
snail but keeping the snails warm in the cooler conditions of
spring and autumn will help to ensure their continuous activity.
Start with a layer of damp gravel. On top add a thick layer of
sphagnum moss or soil and leaf mould.
9
Keep the container constantly humid. Do not place it in direct
sunlight.
Investigating snails
Food
Try pieces of various vegetable matter but note that cabbage
leaves produce rather smelly wastes ! It is most important to
add chalk (lumps or powdered, or as cuttlefish 'bones' but not
blackboard chalk) to provide calcium for shell growth.
Suggestions for a variety of practical activities with snails are
given on the pages which follow. These can be used to encourage careful observations, making measurements, recording
results in various ways, and designing and carrying out simple
experiments. Ideas that pupils come up with about the behaviour of snails can be tested in a 'fair' way. This usually means
changing conditions one at a time to see the effect each has.
A dark cover around the soil layer may encourage snails to lay
eggs next to the sides of the vivarium.
Closely-observed snails
Equally important is the opportunity for children to come into
direct contact with living animals. By the direct observation of
snails, how they move, feed etc, and aspects of their behaviour,
pupils are more likely to appreciate some of the wonder of the
natural world and gain respect for these and other living creatures.
Such close observation cannot easily be achieved by investigating snails in their natural environment. If you have already
perused the section 'All about snails', you will know that when
pupils are most likely to be outside the school class room or
laboratory, studying wildlife in the 'field' (during daylight
hours, when the weather is fine, during the spring or summer),
snails will certainly not be much in evidence. Studying their
behaviour in natural conditions is very difficult.
A flawed code for minibeasts ?
Yet this is exactly what the RSPCA suggests in its "Minibeast
Code" which you may have heard about or seen in RSPCA
educational materials. In the interests of not harming animals,
10
often considered as pests when they eat treasured garden flowers and vegetables and may be killed, or thrown into someone
else's garden !
either individually or as a population in natural surroundings,
the RSPCA recommends a 'hands-off' approach, avoiding bringing minibeast animals into school for studies, and certainly not
investigating their behaviour indoors. This well-meaning attitude to studying minibeasts is, however, flawed. Its overall
effect may be to discourage observations of living animals that
we find all around us, and how then will pupils begin to develop appropriate, caring attitudes ?
1. WHEN ARE SNAILS ACTIVE ?
You will need
Screw-top jars or small boxes; snails; damp cotton
wool; dish of warm water
It is also not true that controlled investigations of minibeasts,
such as snails, brought into schools will be unkind, 'cruel' or
harmful to the animals. Of course, they must be treated with
respect and not subjected to unreasonable or extreme conditions.
However, if snails are, for example, kept warm or cold, wet or
dry, they will only be subjected to conditions which the animals
would normally experience at different times of the year in the
wild. The snails are already well adapted to cope with such
factors.
A. Investigate the conditions which promote activity in snails as
follows.
Place two snails in two dry screw-top jars or boxes. Put one
container in a warm cupboard and one in a refrigerator. Repeat
with two more snails but this time in jars or boxes with some
damp cotton wool.
It is also important for children to appreciate the dangers of
becoming too sentimental about the animals they encounter and
learn not to endow such creatures too often with human feelings
(anthropomorphism). Thus, comments such as "I wouldn't like
to be shut up in a small box all day" when applied to snails (and
many other animals) are inappropriate; after all, the animals
naturally spend much of their time squeezed under stones and
crammed into crevices !
Observe the snails for activity after 15 minutes, an hour and 4
hours. Typical results are as in the table below.
Return to the wild
After a short time in school, the snails can be returned to where
they were collected (except for giant African snails which are
permanent class room residents). This in itself might raise some
important issues to be explored with pupils, since snails are
Try repeating the experiment but keeping the snails cool and
warm, damp and dry, but in the light. What difference does this
make, if any ?
11
B. Put several inactive snails in a shallow dish of warm water.
How long does it take for the snails to move ? When do you
think that snails would be active in the wild ? (Snails may take
from 1-10 minutes to move. The snails have an instinctive reaction to climb out of water; they will not drown !)
A. Look carefully at a moving snail and its shell, foot, tentacles,
lips and mouth. Try to find the breathing hole. Make a drawing
of your snail and label all the parts.
B. Rub an empty snail shell on sand
paper until you have worn it down
to show the inside of the shell.
Use this method of reviving dormant
snails for all subsequent activities.
Draw the pattern you see. How
are all the holes connected ?
2. WHERE DO SNAILS LIVE ?
Where would the body and foot
of the snail be found in the shell
when it draws itself in ?
You will need
Quick-drying paint; fine paint brush
4. INVESTIGATING SNAIL SHELLS
A. Go snail hunting in the school grounds, at home etc. Look in
dark places, at the base of walls, under bricks, stones, pieces of
wood etc. Always replace loose materials as you found them.
Are the snails you find still or moving ? Do they have a seal over
the mouth of their shells ? If the snails are active, is the weather
warm and damp ?
You will need
10% hydrochloric acid (beg some from a local secondary school but take care !); empty snail shells; lump of
limestone/chalk (calcium carbonate); dropper pipette
B. Do snails have a ‘homing’ instinct ? Test this out by marking
snails with paint and tracking where they move. Also, move
marked snails to a new position, and see if they return ‘home’.
A. Carefully drop some dilute hydrochloric acid from a pipette
onto an empty snail shell. What happens ? Is there a difference
when the acid is dropped on the inside and the outside of the
shell ? If so, try to explain why.
3. WHAT DO SNAILS LOOK LIKE ?
B. Now drop acid onto a piece of limestone or chalk. What do
you think the snail shell is made of ?
You will need
Fine sandpaper ; block of wood
C. Leave empty snail shells (including some from young snails
12
B. Look at the shells with a hand lens/magnifier or stereomicroscope. What patterns can you see which show lines of
growth ? Are some bands thinner or thicker than others ?
(Thicker bands show periods of inactivity during growth when
more shell material was made at the lip of the shell.)
if you can) in 10% hydrochloric acid for some time. When the
fizz-ing stops, can you see anything left or has the shell completely disappeared ?
(The periostracum, the outer, horny layer, should remain as a
thin, brown filmy skin. It will be more obvious in young snails in adults it does get worn away. It is usually very noticeable
with pond snails where the outer layer persists throughout life).
C. What shape would the shell be if you could uncoil it ? Try to
measure how long it would be, using some string. Make a model
with plasticine of an uncoiled shell.
To preserve the outer layer, wash away the acid with clean water
and float the periostracum onto a firm piece of paper or card. It
should stick by itself and dry onto the card.
6. MEASURING SNAILS
You will need
Graph paper; ruler; plastic bag; 50 g spring balance or
Newton meter; 10 cm3 and 100 cm3 measuring cylinders;
live snails plus empty shells; beaker or jar; plastic funnel
5. HOW DO SNAILS GROW ?
You will need
Plasticine; thread; ruler; string; paper; scissors;
hand lens; stereomicroscope
A. Put live, active snails on a piece of graph paper. Measure
how wide they are and mark how long their feet are when fully
extended. Do snails with bigger shells always have longer
bodies ?
A. Look at the shells of some snails. What sort of shapes do they
have ? How many turns are there in each shell from the tip to
the open end ? Are they all the same number ? Can you, therefore, tell if the snails are of different ages ? (Note: the maximum
number of whorls is four and a half. Fewer than this shows that
the snail is still growing its shell.)
B. Put a number (say 5 or 10) of live snails in a plastic bag and
hang this from a spring balance to find out how heavy they are.
(Don’t forget to divide by 5 or 10 or whatever for the average
weight of a single snail.)
If you look at the shell from the top, does it turn clockwise or
anti-clockwise ?
Now weigh a similar number of empty shells of the same size. Is
the shell a heavy burden for a snail ?
Make a model of your snail shell with plasticine or cut out the
shell’s spiral shape using paper and hang it up. What other
objects have spirals (eg, screws, pine cones, staircases, springs) ?
C. Find the volume inside a shell by filling an empty one with
water and pouring this into a small measuring cylinder.
13
D. Find the total volume of the live snail and then an empty
shell of the same size by placing each in turn into a beaker or jar
completely filled with water. Catch the water that overflows into
the measuring cylinder, via a funnel. How do the volumes compare ?
C. Let a snail eat parts of a cabbage or lettuce leaf. Does it eat all
parts of the leaf ? (The midribs and veins ar
e often left because
they are too hard.)
D. Leave snails in a container after they have been feeding.
How long does it take for their droppings to appear ? From
which part of the snail do the droppings come ? (Although the
snail feeds quickly it may take up to two days for droppings to
appear from the anus just below the breathing hole.)
7. HOW DO SNAILS EAT ?
You will need
8. WHAT DO SNAILS EAT ?
Flour; dish; spoon; Perspex or glass sheets (with taped
edges); container for snails; dish of warm water; cloth
and tissues or paper towels; magnifier or hand lens; x 20
or x 35 stereomicroscope; snails that have not eaten for
some time; pastry dough, the same consistency as plasticine; lettuce or cabbage leaf
You will need
Snails that have not eaten for some time; shallow trays
with transparent sheets to fit on top; scissors; ruler;
sharp knife; supply of potential foods, eg, lettuce,
dandelion, cabbage leaves, fresh mint leaves, hairy/
prickly leaves; nettles; boiled potato or carrot; onion;
bread; pastry dough; chocolate; egg box cardboard, etc
Preparation Use snails that have been inactive for some time and
will therefore be hungry. Mix flour and water into a very dilute
paste and spread this evenly on Perspex or taped, glass sheets.
Let them dry in the sun or in a warm place, eg, over a radiator.
Preparation Use snails that have been inactive for some time and
will therefore be hungry. Cut up the various foods into equalsized squares or discs.
A. Put a snail in the dish of warm water until it moves. Then
allow it to walk over paper towels and dry its shell gently. Now
place it in the middle of the floured glass sheet. When it is moving, slowly turn the sheet over. Look closely with a hand lens.
Can you see how the lips move ? Describe how the snail feeds.
B. See if a snail will feed on some pastry dough. Then look at
the marks of its ‘tooth prints’ on the dough under a microscope.
There is lots of scope for experimentation, but some suggestions
are given here. It is important that pupils should not feed snails
with unwholesome foods but they will eat most items ! Either
test several snails together or restrict observations to one snail’s
feeding. If necessary, reduce the choice of foods for the snail.
What are the snails ‘teeth’ ? How does it feed on the dough ?
A. Put some equal-sized squares or cubes of bread, boiled pot14
ato (or carrot), onion, pastry dough, chocolate and egg-box
cardboard in a glass-covered tray with 6 snails. Also put equalsized leaf discs or squares of cabbage, dandelion, lettuce, mint,
prickly/hairy leaves and/or nettles in a similar tray with 6 more
snails.
A. Find some garden snails and mark their shells with quickdrying paint. Release the snails in a garden or part of the school
grounds. Look each morning for the next few days for the
marked snails.
How far have they moved ? Where are they found ? Look for
signs of the snails having been eaten; are there any parts of the
shell left behind ? If you cannot find the marked snails, does
this mean they have been eaten ?
Keep both trays moist and so that the snails are not cold.
Look at both feeding trays 1 - 3 days later. Which foods have
been eaten most and least ? You could weigh the pieces of food
before and after or measure areas (see B). Can you suggest any
reasons for the snails' preferences ? Can you recognise any food
remains in the droppings ?
B. From what you know and can discover in books, try to construct a food chain for the snail. For example, grass → snail → ?
(A pack to make your own food chain mobiles for garden and
fresh water animals is available from the Association for Science
Education; see 'Reference materials' section for details. The
garden food chain mobile features snails among the animals that
are illustrated.)
(In a food trial, snails accepted 114 of 200 different kinds of food
offered. Plants with stinging hairs, prickles, strong smells etc, are
often protected from attack. Some leaves, eg, clover, even produce hydrogen cyanide gas when nibbled to deter snails from
continuing to feed !)
C. What time of day do you think that animal predators are
looking for snails to eat?
B. You can find the area of each leaf disc or square before the
investigation by tracing round them onto graph paper. Then
repeat with the partially-eaten material once tests have been
completed. Add up the number of squares on the initial graph
paper tracings and on the tracings of nibbled foods and work
out the total area of leaf eaten.
(Snail predators are mainly nocturnal. Children can look for
empty snail shells at home. Some will be broken. Song thrushes
use a stone ‘anvil’ to try to crack open the shell to reach the snail
inside. They are often unsuccessful !
C. Snails must be given chalk to eat as well. Why is this ?
Snails can also produce a green froth if their soft parts are irritated. This is slightly acidic and may put off some predators.)
9. WHAT EATS SNAILS ?
[At the time of writing (summer 1995), children are invited to
take part in a national survey on snails and song thrushes called
Hammer and Snails, organised by Wildlife Watch and the RSPB.
Contact Wildlife Watch, The Green, Witham Park, Waterside
South, Lincoln LN5 7JR for details.]
You will need
Snails; quick-drying paint; paint brushes
15
10. WHAT CAN SNAILS SENSE ?
D. You can try to find out if snails see colours. Place some snails
which have not fed for some time in a container with a transparent cover. Keep it moist and put four equal-sized pieces of red,
pale green, brown and yellow pastry dough in the bottom. Look
to see which is the commonest colour of droppings in the container after a couple of days. Can you give any reasons for your
findings ?
You will need
Small paint brush; vinegar; dropper pipette; white tile;
pencil; book; ruler; graph paper; pastry dough dyed
with food colouring: red, pale green, brown and yellow
colours; shallow tray or dish with glass sheet for a
cover; card to cover half of the tray; bench lamp; snails
- some that have not eaten for some time
(The bottom tentacles are chemosensory, ie, used for smelling
and tasting, but all the body can be used for smelling. As snails
are mainly nocturnal, it is likely that they detect their food by its
scent.
A. Touch different parts of the foot carefully with the tip of a
small paint brush. What does the snail do ? Touch the snail’s
shell. Can it feel you ?
You could test this out by making up a simple Y-maze. This
could perhaps be cut out of a block of polystyrene with a glass
or Perspex cover, or using wide bore PVC tubing. (You can get
that from builders’ merchants). Place a hungry snail at the end
of the bottom of the Y. Place some food at the end of one of the
top arms of the Y; cover it so that it cannot be seen. Then note
which way the snail turns at the junction of the Y. Repeat lots of
times, moving the food to the other arm of the Y. Does the snail
move towards the food, whichever arm of the Y it is in ?
B. Dip a brush into vinegar and hold it near the snail. Does it
move ? Look carefully at the tentacles. Paint a ring of vinegar on
a board around an active snail. Will it cross the ring ? Also paint
a ring of water around the same snail. (This is called the control
for the experiment; it may just be any liquid that the snail reacts
to.) How and why does the snail react to both liquids ? Which
tentacles are used in testing the surface and the liquids ? Why
does the snail need to smell ?
Snails react to shadows, particularly when they move. Snails
usually move into the dark. They move away from light but the
light also produces heat, so the snail may be moving away
because of the heat and not the light. Try filtering out the heat
from the lamp by shining the light through cold water to discover which stimulus is the most important - heat or light.
C. Carefully move a pencil near the tentacles; then a book. How
does the snail react ? With a ruler you can measure how near an
object can be moved before the tentacles move. How do the
tentacles move ? Cast the shadow of an object onto the tentacles.
Which tentacles are used for seeing and which for smelling ?
Place several snails in the middle of a tray or dish. Put a card
over one side and shine a light over the open side. Where are the
snails after 5 and 10 minutes ? Why do you think the snails
behave in this way ?
Tests have shown that snails mainly feed on coloured foods,
such as pastry dough, that are pale green. This might suggest
that they can see some colours at least, which would be useful
for daylight manoeuvres.)
16
[Snails have a tendency to move upwards away from gravity
but this is only strongly shown if the snail has been immersed in
water (or rained on in the wild). You can try making a snail seesaw which sits in a trough of water and tips up as soon as the
snail moves up out of the water, towards the top of the see-saw,
so depositing the snail back in the water again !
11. INVESTIGATING SNAILS MOVING
You will need
Dish of warm water; cloth or tissues; Perspex or
2
glass sheet; 1 cm
wire mesh; talcum powder; black
card; snail see-saw (optional)
A. Put a snail into the dish of warm water. When it starts to
move, let it walk on some paper towels, dry its shell gently and
put it on a Perspex or taped, glass sheet. When it is firmly attached, slowly turn the sheet upside down. What sort of movement can you see from underneath ? Draw any patterns you
can see on the snail’s foot.
B. How can you know where a snail has been moving without
watching its every move ? Does it move in straight lines ?
Then the snail starts to climb up and off we go again ! This seesaw only works well with large, heavy snails (giant African land
snails are ideal). A little drop of washing-up liquid in the water
helps the see-saw to tip up more easily (by reducing surface
tension in the water) when the snail moves up to the top.]
(One way of tracing where a snail moves is to dust the glass
afterwards with talcum powder. This sticks to the slime trail left
by the snail. Alternatively, make the snail walk on a piece of
black card or paper. The slime trail again shows up well.)
C. Put some snails on the wire mesh. What do the snails leave
on the wire ? Look from underneath to see how they move
differently compared to when they are on the Perspex/glass.
12. SNAILS AND SURFACES
You will need
Active snails; various grades of sand/emery paper
from rough to smooth; dishes of different sizes of particles from, eg, soot, flour etc through coarse sands and
grits to gravel; shallow dish or tray with cardboard
partitions
D. Put some snails in the middle of a sheet of Perspex/taped
glass. See where the snails move when the sheet is horizontal.
Now tilt the glass at 45° and then hold it vertically. Where do the
snails move each time ? Try this also on the wire mesh. Does it
make a difference if the snail is dry or wet before you test its
movements on a slope ?
17
A. Place active snails on different surfaces with varying degrees
of smoothness or roughness and particle size. Compare how
easily or quickly the snails can move on each.
pen or quick-drying paint. Put all the snails on the starting point
in the middle of the circle and see which snail passes the finishing line first. Does the favourite always win ?
What surfaces prove more difficult for the snails ? (Gardeners
used to protect their plants from snail attack by spreading a
thick layer of soot or fine ash on the ground around the plant.
Do you think this would have worked from what you have
found ?)
B. Put one active snail on the centre of a large card. Follow the
route of the snails with a pencil for exactly one minute. Lay a
piece of string along the route taken and then measure the
length of the string with a ruler. Try this several times and work
out the average. How far could your snail travel in one hour ?
B. Try to find out if snails have any preferences for the surfaces
they walk on. Divide a shallow tray or dish into different areas
with cardboard spacers or partitions. Fill each area to the same
depth with different materials and place an active snail in the
middle. Repeat with other snails.
C. Repeat the timing exercise with snails kept in warm, cold,
damp and dry conditions beforehand. When do snails move
fastest and slowest ? What do you think would happen in the
wild when the weather changes ?
14. HOW STRONG ARE SNAILS ?
Where do the snails choose to walk ? Repeat the tests several
times. Try moving the tray around in case it is on a slope and the
snails are just moving according to their response to gravity.
Does it make a difference if the surfaces are moistened ? How
could this be important for snails in the wild ?
You will need
String; 100 g and 250 g (1 N and 2.5 N) spring balances
(the latter for giant African snails); Perspex or taped,
glass sheet; clamp and stand; wooden board with hook
13. SNAIL RACING AND TIMING
A. Place a snail on a sheet of glass placed vertically. Attach it to
a spring balance with string tied round the snail’s shell; see next
page for illustration. How much force can the snail exert as it
moves upwards ? Does the slope of the glass sheet make any
difference to the force that a snail can exert ?
You will need
Snails and a means of marking them to identify individual specimens; large black card or plastic sheet with
large circle marked on it; pencil; string; ruler; stopclock
B. Snails cling to objects. To see how much force is needed to
dislodge a snail, tie some string, attached to a spring balance,
round the shell and pull upwards when the animal has clung to
various surfaces.
A. Put a large black card or plastic sheet with a large marked
circle on the floor. Clearly mark your snail’s shell with a felt tip
18
15. HOW DO SNAILS BREATHE ?
You will need
Dishes of warm water (30 °C) and cold water (5 °C);
land and pond snails
A. Look at a snail upside down. Look for the breathing hole on
the right-hand side just beneath the shell lip. The hole opens and
closes as air is drawn into and out of the snail’s ‘lung’.
B. Place one snail in warm water and another in cold water for
a few minutes. Take one snail out and hold it upside down.
How many times is the air hole opened in 5 minutes ? Now do
the same with the other snail. What makes the air hole of this
one open differently ? How is the breathing rate related to the
snails’ activity ?
(A force of up to 60 g is typically needed to dislodge a snail.
Snails can lift 10 times their own mass up a vertical surface - the
equivalent of a man lifting a ton !)
C. Put one pond snail in each container of water and look at
them through the sides. Do they breathe in the same way as the
land snails ?
(The air hole opens and closes more often in warmer and
moister conditions when the snail is likely to be most active and
require most air.)
19
Mobile Pack
ISBN 0863571964 £1.95
(An excellent 'cut up and hang' pack to construct food chain
mobiles for fresh water and garden organisms. The garden
mobile features snails. Formerly published by the 'Centre for
Life Studies'.)
Reference materials
A wide range of learning materials is available on snails, the
mollusc group to which they belong or minibeasts in general.
BOOKS AND PACKS
Non-Aquatic Animal Identification Keys
J Marson (School Natural Science Society Publications) £2.00
(A collection of simple keys to aid identification of minibeasts.)
AMS Educational
Woodside Trading Estate, Low Lane, Horsforth, Leeds
LS18 5NY. Tel: 0113-258 0309; Fax: 0113-258 0133
Snails and Slugs
E M Tuke (School Natural Science Society Publications) £1.00
(Background information on snails for the teacher.)
Investigating Minibeasts
Complete pack ISBN 0746619766 £55.00
Individual cards £3.00 Pack of 5 same cards £13.75
(An excellent pack to help in identifying and studying minibeasts, with 20 full-colour fold-out investigation cards and
teachers’ guide + 2 identification charts (with complete pack).
One card is on snails; another deals with slugs. Individual cards
can be purchased separately.)
Belitha Press
Orders to Bailey Distribution, The Book Distribution Centre,
Learoyd Road, Mountfield Industrial Estate, New Romney,
Kent TN28 8XU. Tel: (01797) 366905; Fax: (01797) 366638
The Wildlife Activity Book
C Watson ISBN 1855613034 £6.99
(A book for 6-9 year olds which includes some work on snails.)
Apple Press
D Services, 6 Euston Street, Freemen’s Common, Leicester
LE2 7SS. Tel: 0116-254 7671; Fax: 0116-254 4670
A & C Black
P O Box 19, Huntingdon, Cambs PE19 3SF.
Tel: (01480) 212666 ; Fax: (01480) 405014
Shells
F Woodward ISBN 185076431X £4.95
(A guide to identifying animals by their shells; includes some
references to snail shells.)
Stopwatch Books: Snail
ISBN 0713634987 £3.50
(An excellent paperback title giving a photographic guide to the
development and changes in a snail’s life. Accompanying text
combines simple bold headings for younger readers, together
with more detailed information for older children.)
Association for Science Education
College Lane, Hatfield, Herts AL10 9AA.
Tel: (01707) 267411; Fax: (01707) 266532
20
Land and Water Invertebrates (Identification in the School Grounds)
L Merrick ISBN 1857410866 £6.95
(Provides photocopiable identification sheets for species most
likely to be found, together with a variety of other materials.)
Collins Publishers
Harper Collins Distribution Services, PO Box, Glasgow, G4 0NB.
Tel: 0141-772 3200; Fax: 0141-762 0584
A Field Guide to the Land Snails of Britain and N W Europe
Kerney & Cameron ISBN 000219676X £14.99
(A detailed reference guide for snail identification.)
Slugs, Snails and Earthworms (A practical guide to their study in
School Grounds via the National Curriculum)
J Feltwell ISBN 1872865054 £4.50
(A first-rate publication encouraging hands-on work with lots of
ideas for collecting, handling and observing these animals.)
Kingfisher Books
Elsley House, 24-30 Great Titchfield Street, London W1P 7AD.
Tel: 0171-631 0878; Fax: 0171-323 4694
Science in the School Grounds
G Thomas ISBN 1857410858 £7.95
(An excellent book which shows the potential of using the
school grounds for a variety of activities.)
Minibeasts
ISBN 086272743X £2.95
(A paperback title in the ‘Fun with Science’ series for 8-12 year
olds which includes some material on snails.)
Stanley Thornes
Ellenborough House, Wellington Street, Cheltenham, Glos
GL50 1YD. Tel: (01242) 577944; Fax: (01242) 221914
Oxford University Press
Educational Division, Walton Strret, Oxford OX2 6DP.
Tel: (01865) 56767; Fax: (01865) 56646
An Early Start to Nature
R Richards ISBN 0750100443 £9.99
(Ideas for practical activities with children up to Year 6.)
Slugs and Snails
T Jennings ISBN 0199182647 £3.50
(A paperback title in the ‘Into Science’ series which provides
colourful information and suggestions for activities.)
Small Garden Animals
T Jennings ISBN 0199170363 £3.50
(A paperback title in the ‘Young Scientist Investigates’ series
which contains some information and activities on snails.)
Learning Through Science Series:
All Around
ISBN 0356075532
Moving Around ISBN 0356075559
Which and What ISBN 0750100230 All packs £18.99
(Excellent work cards which contain some useful materials on
snails. Originally from Macdonald Education/Simon & Shuster.)
Southgate Publishers
Glebe House, Church Street, Crediton, Devon EX17 2AF.
Tel: (01363) 777575; Fax: (01363) 776007
Usbourne Publishing
D Services, 6 Euston Street, Freemen’s Common, Leicester
LE2 7SS. Tel: 0116-254 7671; Fax: 0116-254 4670
21
Creepy Crawlies
ISBN 0860206300 £2.50
(A paperback title in the ‘First Nature’ series for 5+ year olds,
providing colourful information on minibeasts in general.)
Discovering Slugs and Snails
Wayland Publishers
How to Begin the Study of Slugs and Snails
J Sankey
Richmond Publishing Company
Life Cycle of a Snail
Wayland Publishers
The Snail T Buholzer
Dent
Snails (Natural Science series)
Lerner Publications
Snails (Nature Close-ups series) Young Library
Snails (Observing Nature series) Wayland Publishers
Snails J Coldrey and J Harland Puffin Books
Shells
ISBN 0860202755 £2.75
(An identication book in the ‘Spotter’s Guides’ series which
includes some reference to snail shells.)
Watts Publishing Group
96 Leonard Street, London EC2A 4RH.
Tel: 0171-739 2929; Fax: 0171-739 2181
SLIDES AND FILMSTRIPS
Drake Educational Productions
St Fagans Road, Fairwater, Cardiff CF5 3AE.
Tel: (01222) 560333; Fax: (01222) 554909
Snails and Slugs
ISBN 0863136915 (Hbk) £7.99 ISBN 0749614129 (Pbk) £4.50
(Colourful information book in the ‘Keeping Minibeasts’ series
showing how to look after these animals.)
Looking at Molluscs 96956 £12.00
(Filmstrip/notes on the animal group to which snails belong.)
Wayland Publishers
61 Western Road, Hove, East Sussex BN3 1JD.
Tel: (01273) 722561; Fax: (01273) 329314
Focal Point Audio Visual
251 Copnor Road, Portsmouth, Hants PO3 5EE.
Tel: (01705) 665249; Fax: (01705) 695723
Keeping Minibeasts
ISBN 0750216220 £9.50
(A title in the ‘Nature Projects’ series of lively, activity-based
books for KS 2 work.)
Biology of Molluscs
£14.75 (20 colour slides plus teaching notes for wider studies of
the group to which snails belong.)
Philip Green Educational
112a Alcester Road, Studley, Warwickshire B80 7NR.
Tel: (01527) 854711; Fax: (01527) 854385
OUT OF PRINT BOOKS
In recent years, large numbers of books have been published on
snails but are no longer on sale. You may be able to track these
down via local public or LEA libraries. Some of the titles to look
out for are listed here.
Small Creatures
F23 Filmstrip £5.00
(56 half-frame strip with some material on snails included.
22
Looking for Shapes 1 F37/S37 Filmstrip/slides £5.00
(56 half-frame strip or 24 full frame slides with some material on
snails included.)
The Biology of Molluscs and Animals Without Backbones
Single-user licences: £29.00
(13-minute videos showing the characteristics of this group of
animals and an overview of invertebrate animals.)
PICTURE PACKS & WALLCHARTS
Philip Green Educational
112a Alcester Road, Studley, Warwickshire B80 7NR.
Tel: (01527) 854711; Fax: (01527) 854385
Looking for Shapes 1
Small Creatures
P37 Poster Pack £10.00
P56 Poster Pack £10.00
(12 beautiful A4 photographs in each pack with some material
on snails included.)
Small Creatures 1 & 2
£10 double pack
(An excellent-value collection in the ‘Pictures & Poems’ series
which provides two packs each containing 12 superb A4 colour
photographs with accompanying poems. Both sets include some
material on snails.)
PCET Wallcharts
27 Kirchen Road, London W13 0UD.
Tel: 0181-567 9206; Fax: 0181-566 5120
Keeping Minibeasts T763 £8.27
(A set of 4 charts on frogs, snails, worms and spiders.)
VIDEOS
Viewtech Film and Video
161 Winchester Road, Brislington, Bristol BS4 3NJ.
Tel: 0117-977 3422; Fax: 0117-972 4292
23
Topic web
Length, mass
& volume
Extinct
animals
Spirals
and
cones
Classification
Fossil
shells
Grouping
Banding
patterns
Shells
Other animals
with shells
Camouflage
Animal
homes
Tides
Seashore
Sand
Molluscs with
& without shells
Shelters
Studies
of snails
Insects
Hiding from
predators
Rock
pools
Sea animals
Colour
Worms
Slugs
Pond
snails
Other wildlife in
ponds and streams
Wildlife in
school
grounds
Other
minibeasts
Woodlice
Spiders
Seasons
Climate
Light
Hibernation
in winter
Aestivation
in summer
Heat &
the Sun
Finding
the best
conditions
Moisture
and rain
Senses
Speed
Animal
tracks
Touch
Food &
feeding
Taste &
smell
Ways of feeding
in other animals
Movement
Snail races
Sight
Reproduction
Slime
trails
Legs in
other
animals
Eating
snails
Snail development
and growth
Eggs
Feet
25