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Joseph Calistan Biology coursework
Investigating the effect of temperature on the behaviour of maggots
Abstract:
The main aim of the investigation was to determine how external temperature affected the
metabolism of 'Calliphora vicina' (The bluebottle blowfly) larvae.
Rationale for the investigation:
'Calliphora vicina' larvae, more commonly known as 'Bluebottle blowfly Maggots', are a very
important part of the ecosystems they inhabit. They help dispose of 'waste' in the environment, by
colonising corpses and consuming the dead tissue. This helps remove a biohazard in the
environment, as dead corpses are a haven for harmful bacteria.
This is important, as, due to their relative abundance, and the 'Calliphora vicina' blowfly's highly
sensitive sense of smell, they tend to reach the corpses quickest after death, and colonise it in the
largest numbers, when compared to other insects (1).
So, by investigating how temperature affects a maggots metabolism, the information gathered
about the effect of temperature around a body/larvae could suggest that it affects the rate that the
maggots eat, and grow and then pupate, which could help improve the accuracy of forensic
entomology, which will help decrease the number of unsolved crimes.
Maggots cannot control their own body temperature, and are cold blooded, so external temperature
determines the temperature of their ECF (extra-cellular fluid, the fluid surrounding all cells, which
controls their temperature, and individual cell metabolism) and therefore their overall metabolism
(2). However, as maggots live in colonies, the maggot mass can raise the temperature inside the
colony by anything from 5-20°C when compared to external conditions, due to the large amount of
metabolic activity, which can confuse the estimated age of maggots on a corpse when compared to
the external temperature over the time period (3).
As a maggots rely on the external temperature to control their internal temperature and metabolism
(4), and metabolism is directly linked to its rate of growth, the effect of temperature on an individual
maggot can be used to improve the accuracy of estimation of a bodies age post-mortem, as we
already know how the maggot mass effects the temperature around the individual maggot.
Metabolism is controlled by enzymes, and enzymes have an optimum temperature at which they
work most efficiently. In maggots, the optimum temperature is around 27°C, which is slightly
warmer than average outdoor conditions.
Enzymes break down chemicals in the body into the necessary chemicals for survival, like sugars, and
the more efficiently they work, the more energy the body has to use for exercise and general
'upkeep' such as respiration.
My hypothesis:
My hypothesis is that the maggots will become travel further as the temperature increases, but may
decrease at the higher temperatures (around 40°C) due to the enzymes starting to denature.
Null hypothesis:
My null hypothesis is that the maggots will not travel any further as the temperature increases, and
will not change at the higher temperatures, and the enzymes will not denature
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Joseph Calistan Biology coursework
Trial experiment:
I will be carrying out a trial experiment to ensure that my method is feasible, and that all the
equipment is working to a certain degree of accuracy.
I will be checking whether the intervals in temperature are appropriate, and whether I would have
to decrease the intervals to +5°C each time.
Also, I may have to use less maggots per temperature to ensure I can complete my experiment in the
time period, while still getting enough data to draw an average value.
I may also need to source new equipment, such as a functioning water bath, or a working timer, and
I have to check that the maggots will react to the changing temperatures, and if they don't, I will
have to see why this is, and whether I can find a new method that will be applicable.
Method and Equipment list:
I will be using a water bath to heat a metal tray with a set course for the maggots to travel, and I will
measuring the distance they travel in 1 minute. I will be measuring 5 maggots per temperature
(10°C, 20°C, 30°C and 40°C) to get a usable average, while still staying within the time constraints of
my schedule. The variables I will be controlling/measuring are:
Variables:
The distance they travel (dependent variable)
The temperature of their surroundings (independent variable)
Time that their movement is measured for (control variable)
Type/Species of maggot (control variable)
Age of maggot [all maggots in sample should be the same] (control variable)
Number of maggots measured per temperature (control variable)
The route upon which they can travel (control variable)
The light conditions [as they are carried out in a well lit room, this should have no effect on
results] (control variable)
Equipment list:
Equipment
Maggots
Water bath
Thermometer
Ruler
Metal tray
Stand
Wooden blocks
Timer
Card
Paint brush
Reason
To measure their response to increased temperature
To control the temperature of the maggots surroundings
To ensure the temperature of surroundings is correct
To measure distances travelled by maggots
To protect the maggots from the hot water (drowning)
To support the metal tray out of the water
To create a path for the maggots to follow
To measure 1 minute of maggot travel
To assist in the safe travel of maggots
To assist in safe acquirement of maggots
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Joseph Calistan Biology coursework
Preliminary report:
From the results that I gathered, I can see that there may be a few problems with my method:
Method problems:
Some maggots managed to turn around in the pathway, ruining some of the runs, as
measurements cannot be made in reverse with the current equipment.
Some maggots managed to escape under the wooden blocks which make up the pathway
also wasting time.
The ruler can only measure straight lines, which is not how maggots travel.
Some maggots were different ages, and could therefore have varying metabolism rates, and
therefore have travelled varying distances.
Some maggots did not move at all, due to a defensive reaction of ‘playing dead’ upon being
handled.
Solutions:
The pathway needs to be altered so the maggots cannot change direction, or that reverse
travel can be measured.
The pathway needs to be made secure to avoid escapees.
I will follow the maggot’s pathway by drawing its pathway on a plastic cover from above as it
moves, then use string to follow this path, and then measure the length of string. This will
allow more accurate distance measurements
I will identify maggots of the same age using a chart in the biology book to avoid age
variation.
I will allow the maggots some time on the metal tray before I start the timer, to overcome
their defence mechanism and to allow them to adapt to the temperature around them.
The type of water bath used in my experiments.
(Source: http://www.cmu.edu/bio/resources/surplus_goods.html )
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Joseph Calistan Biology coursework
Results:
Distance travelled (cm)
Temperature °C
(Room temp)
maggot 1 maggot 2 maggot 3 maggot 4 maggot 5 Average
10
3
1
2
4
6
3.2
20
5
8
4
3.2
4.9
5.02
24
3
9
3.5
7.8
5.1
5.68
30
10.5
27
15
19.4
17
17.78
40
13
15
12
9
18
13.4
Average Distance crawled by magoot
(cm)
Preliminary results average
20
15
10
5
0
0
10
20
30
40
50
Temperature (°C)
While the graph does show a general rise in average distance travelled, with a drop off at
40°C, the results table shows some rather large variation between distances travelled at the
same temperature. This could be because of varying age of maggots, and their temperature
before the experiment.
I included the 27cm in the average of 30°C as, during the preliminary experiment, I was
unaware that some of my maggots were of various ages, and could therefore not classify it
as an outlier.
I can make sure that my final results are less varied by correcting my method, as seen above.
The age of the maggots alters how their metabolism works, and therefore their reaction to
temperature change, so I will have to ensure the age of the maggots I use in my experiment
by using the chart in the Salters-Nuffield Advanced Biology (SNAB) A2 text book.
This will help remove any ‘outliers’ (non-includable results).
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Joseph Calistan Biology coursework
Actual experiment planning:
For my Actual experiment, I have corrected the method and equipment I will be using:
Corrections to experiment:
The Age of individual maggots used will be added as a control variable that needs to be
checked before results can be used.
Instead of using a Ruler to measure the distance, I shall place clear plastic above the maggot
tray and follow its path with string and blu-tack, then, after the experiment, measure the
length of string, for a more accurate measurement. (This also allows reverse travel to be
measured).
The maggots will be allowed time to adapt to their surroundings, so that they are not still in
their defensive ‘playing dead’ mode, and can then be measured equally.
The pathway has been reconstructed so there are no cracks/gaps for maggots to use to
escape the pathway.
Equipment list (corrected):
Equipment:
Maggots
Water bath
Thermometer
String
Blu-tack
Marker pen
Ruler
Metal tray
Stand
Wooden blocks
Timer
Card
Paint brush
Reason:
To measure their response to increased temperature
To control the temperature of the maggots surroundings
To ensure the temperature of surroundings is correct
To measure distances travelled by maggots
To keep the string in place during the 1 minute
To mark where to stop measuring the string
To measure string.
To protect the maggots from the hot water (drowning)
To support the metal tray out of the water
To create a path for the maggots to follow
To measure 1 minute of maggot travel
To assist in the safe travel of maggots
To assist in safe acquirement of maggots
How will my results be analysed:
As I have two variables I need to investigate the link between, I will be using the Spearman rank
correlation to ensure that there is a strong correlation between the distances travelled (linked to
metabolism) and temperature. (Spearman rank proves correlation between 2 variables)
This will give me a percentage of certainty in my hypothesis from my results, and allow me to say for
certain how likely it is that there is a link between the variables.
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Joseph Calistan Biology coursework
Actual experiment:
Results:
Temperature °C
(Room temp)
Distance travelled (cm)
maggot 1
maggot 2
maggot 3
maggot 4
maggot 5
Average
10
10.1
9.8
8.9
9.3
12.1
10.04
20
13.4
14.2
12.9
15.3
14.7
14.1
24
15.1
17.4
13.8
17.2
16.7
16.04
30
23.2
25
27.1
26.4
20.5
24.44
40
21
18
19
17
16.5
18.3
Distance crawled by maggot (cm)
Final results averages
30
25
20
15
10
5
0
0
5
10
15
20
25
30
35
40
45
Temperature (°C)
From these results, we can see that, once again, after 30°C, the average distance travelled by
maggots decreased. We can also see that the average distance travelled increased quicker from
above room temperature (24°C) until 30°C, where it peaks. This suggests that the optimum
temperature for maggots is around 30°C.
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Joseph Calistan Biology coursework
Spearman’s rank correlation:
Table:
Temperature (°C)
10
20
24
30
40
Rank
temp.
1
2
3
4
5
Average distance travelled
(cm)
10.04
14.1
16.04
24.44
18.3
Rank
Dist.
1
2
3
5
4
Difference (D)
0
0
0
-1
1
D²
0
0
0
1
1
15
0
2
Equation:
Maths:
𝑟 =1−(
6(2)
)
5(25 − 1)
r = 1 - 0.1 = 0.9
Spearman rank correlation critical value for 10% at 5 values = 0.9
My results = 0.9
I can be 90% sure that Temperature and maggot metabolism are
linked.
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Joseph Calistan Biology coursework
Evaluation: