“Insect-O-Rama”
Aquatic Insects
Workshop on aquatic insects: collection,
basic ecology, and recognition of major orders
Developed by Lindsay Stallcup
UGA Costa Rica / Ecolodge San Luis
Institute of Ecology, University of Georgia
June 2006
Contact Academic Programs Coordinator if you have questions,
suggestions, or corrections. Gracias!
Updated 19Dec09, LAS
“Insect-O-Rama” – Aquatic Insects
Equipment needed
Take to field: D-frame nets, Surber sampler, white plastic bowls or pans for collecting/sorting
Vials and containers for sorting
Forceps, hand lenses
Have in lab:
Alcohol for preserving & viewing samples
Microscopes & lights
Outline of Workshop
Part I. How do we collect aquatic insects?
A. Review methods for collecting aquatic insects
- D-frame / kick nets: place straight metal part of net frame on stream bottom and disturb area
just upstream of the net (qualitative sample)
- Surber sampler: place frame of sampler on stream bottom and disturb the substrate within
the frame. This is the same idea as the kick net, but gives you a known area (more
quantitative)
- Pick up rocks and remove insects using forceps, or scrub carefully with a brush
- Sweep surface of pools or ponds to collect water striders and other surface-dwelling insects
B. Review different habitats in which students might collect insects – streams & rivers (riffles and
pools); wetlands; bromeliads; water tanks; anywhere else water tends to collect
Part II. Field collection of insects
A. Distribute nets, Surber sampler, plastic bowls/pans, vials, and forceps to students for collecting
B. Take students into field for collection of insects. Possible sites close to the Ecolodge include:
Streams:
Rio Alondra & tributary where they cross the road, past Cabina gate/entrance
Rio San Luis, could be done on hike to waterfall
Wetlands:
Laguna/pond on left side of road after passing entry road to Cabinas
Part III. Insects – overview of ecology, morphology, and common orders
A.
B.
C.
D.
E.
What is an insect? Basic overview of taxonomy; characteristics shared by all insects
Why do we care about aquatic insects? Ecological roles & importance
Feeding habits – functional feedin groups
Life cycle – metamorphosis
Overview of some common orders – in order from most primitive to most advanced:
Hemimetabolous
Ephemeroptera
Odonata
Plecoptera
Hemiptera
Holometabolous
Megaloptera
Coleoptera
Trichoptera
Diptera
For each order, give the following:
1. metamorphosis – hemi (“incomplete”) or holo (“complete”)
2. meaning of name (ex: Coleoptera = “sheath wing”)
3. common names, examples
4. mouthparts & feeding habits
5. habitats
6. identifying characteristics
Part IV. Identifying & grouping insects that have been collected
A. Have students work in groups of 2-3 to sort insects according to order. Focus should be on
visual identification and on getting orders – not on getting things to family, species, etc. It’s
okay to make a category for “unknowns.” Instructor can circulate and check accuracy and
answer questions.
B. When small groups have finished, combine groups to get a “class collection,” labeling the
orders and putting “like species” together.
C. Class collection can be compared with existing collections. This should be saved until the END
of the activity – idea is for students to rely on their own classifications first, then compare later.
What is an insect?
What do we mean when we call something an insect? All forms of life are classified by
taxonomists according to the following scheme of classification. Each category is called a “taxon.”
Here is an example of how insects would be classified:
Domain: Eukaryota
Kingdom: Animalia (animals)
Phylum: Arthropoda (arthropods)
Class: Insecta (insects)
Order: we will be covering the major orders of aquatic insects today
Family
Genus
Species
Basic characteristics of insects. All insects have the following during at least some life stage:
- head, thorax, and abdomen
- 3 pairs of legs
- 2 pairs of wings
- 2 antennae
A. Why do we care about aquatic insects?
 Aquatic insects can be found anywhere there’s water: streams, rivers, wetlands, drains, etc.
 Aquatic insects are often the larvae of terrestrial adults, although some are always aquatic.
 Aquatic insects play important ecological roles:
- They are a major food item for many birds, fish, frogs, bats, etc. Even if they’re not a food
item in the aquatic life stages, they may be as winged/terrestrial adults.
- Abundance & diversity of aquatic insects can tell us a lot about ecosystems:
- Different aquatic insects have different tolerance levels to pollution and/or habitat alteration.
- Some aquatic insects are sensitive to pollution: if a stream or river becomes polluted, they will
die or move elsewhere.
- Others aquatic insects are tolerant of pollution, meaning they can survive in polluted water.
- Aquatic insects also require suitable habitat, including a good selection of rocks, logs, silt and
plants in and along the edge of the river or stream. If suitable habitat is not present, aquatic
insects will not be able to survive in that location.
C. Feeding habits
All aquatic insects fit into one or more of these “functional feeding groups,” depending on what
and how they eat:
- Filterers feed on organic matter in water column (algae, particulate organic matter, detritus)
- Collectors consume small particles of organic matter from the sediment (algae, POM, detritus)
- Shredders are herbivores that consume mostly leaves. They are important in breaking up
leaves into smaller particles, which can then be consumed by filterers and collectors.
- Scrapers are also herbivores. They feed mostly on algae, which they scrape off rocks or wood.
- Predators eat other aquatic insects or other small invertebrates, or sometimes even small fish.
D. Life cycle – metamorphosis
Metamorphosis refers to a major change of form or structure during development.
Metamorphosis is one of the key reasons why insects are so successful. Many insects have immature
stages with completely different habitats from the adults. This means that insects can often exploit
valuable food resources while still being able to disperse into new habitats as winged adults. The
potential for adaptation and evolution is greatly enhanced by metamorphosis.
Within the class Insecta, there are 3 subclasses:
Ametabola – only 2 orders, won’t talk about today
Hemimetabola
Holometabola
The “older” or more primitive condition is hemimetabolous, or “incomplete metamorphosis.”
Hemimetabolous insects do not have a pupal stage. The general appearance of the immature stages
is somewhat similar to that of adults, although there may be some dramatic differences in lifestyle.
Only adult insects are able to reproduce, and only adult insects have functional wings (in those
species that have wings). The immature stages of these insects are generally called nymphs rather
than larvae.
Holometabolous, or “complete metamorphosis”: Many of the major insect orders have a typical life
cycle which consists of an egg, which hatches into a larva which feeds, molts and grows larger,
pupates, then emerges as an adult insect that looks very different from the larva. These insects are
often called 'Holometabolous', meaning they undergo a complete (Holo = total) change (metabolous =
metamorphosis or change).
Typical life cycle of a holometabolous
Insect, such as an ant
(egg, larva, pupa, adult)
Typical life cycle of a hemimetabolous
insect such as a dragonfly
(egg, various instars/immature phases, adult)
Order Ephemeroptera
Metamorphosis
Incomplete
Meaning of name
From the Greek "ephemera" meaning short-lived, and "ptera"
meaning wings – reference to short lifespan of most adults.
Common names
Mayflies
Mouthparts and feeding habits
Scrapers, collectors, filterers
Habitats
Various habitats in streams, rivers, ponds
Identifying characteristics
Immatures:
- Antennae short and bristle-like
- 4-9 pairs of leaf- or fan-like gills along sides of abdomen
- Three long filaments at rear of abdomen (rarely two)
Example of immature mayflies (naiads)
Example of adult mayfly
Facts about Ephemeroptera:
- Many northern lakes and rivers in U.S. & Europe support large populations of mayflies.
- In some mayfly species, summer emergence of winged stages is a sudden and dramatic event that occurs
almost simultaneously throughout the entire population.
- Mayflies are a favorite bait of fishermen, and many popular fishing "flies" resemble mayflies.
- The immature stages of mayflies are aquatic. They generally live in unpolluted habitats with fresh, flowing
water. They can be "ecological indicators" of good water quality and are an important source of food for
fish and other aquatic wildlife.
- The life cycle of mayflies is unique among hemimetabolous insects in that larvae emerge into a shortlived, usually sexually immature, subimago or sub-adult stage prior to molting into the sexually mature
adult. The mayfly adult typically survives for only a few hours, just long enough to mate and lay eggs.
- Females lay their eggs by flying low over the water surface and dipping an extruded egg sac into the
water. In some species that inhabit swift flowing water, the female will crawl under the water surface to
lay her eggs directly on submerged rocks. The duration of the egg stage can range from a few days to a
number of months. Larvae undergo a number of instars (growth stages) depending on species and
conditions.
Order Odonata
Metamorphosis
Incomplete
Meaning of name
From Greek “odonto” – meaning tooth
Common names
Two suborders:
Dragonflies (suborder Anisoptera)
Damselflies (suborder Zygoptera)
Mouthparts and feeding habits
Predators
Habitats
All types of standing or running water; many live in vegetation or
debris. Some can live in tree holes or bromeliads.
Identifying characteristics
All Odonata have a hinged labium ending in sharp jaws
Dragonflies have a robust body ending in three sharp spines
Damselflies have a long, slender body and three flat, leaf-like gills
at rear of abdomen (looks like a tail)
Spanish name
Libélula
Facts about Odonata:
-
Ancient insects that have been around since before the age of the dinosaurs. Some Odonate fossils
from the Carboniferous period had wingspans of over a meter!
-
Some odonates can shoot out their labium and catch prey in only 25 milliseconds. They feed on other
aquatic insects, and even small fish and tadpoles!
-
Many adult male dragonflies establish and defend territories along the perimeter of a lake or stream.
Females will mate only with males that hold a territory.
-
Male damselflies (and perhaps some dragonflies) have a special flagellum associated with the
copulatory organ that can reach into a female's body and remove sperm deposited by another male in a
previous mating.
Example of dragonfly adult and immature
Example of damselfly adult and immature
Order Plecoptera
Metamorphosis
Incomplete
Meaning of name
From Greek "pleco" meaning folded and "ptera" meaning wing,
refers to the pleated hind wings which fold under the front wings
when the insect is at rest
Common names
Stoneflies
Mouthparts and feeding habits
Scrapers/grazers (algae)
Important as shredders in North America
A few (2 families) are predators of other small aquatic insects
Habitats
Under stones/rocks
Usually in clean, fast-moving, well-aerated water
Identifying characteristics:
-
Two cerci (“tails”)- usually long & multi-segmented
Antennae long, filiform
Body flattened, legs widely separated
Gills look like "tufts" behind head, at base of legs, or around anus
Each segment of thorax is covered by a large dorsal sclerite
Facts about Plecoptera
-
Stoneflies require clean, well-oxygenated water to survive. They are extremely sensitive to water pollution
and are used by ecologists as indicators of water quality.
-
Stoneflies are also an important source of food for game fish (e.g., trout, bass) in cold mountain streams.
-
Stoneflies are most abundant in cool, temperate climates – not especially common/diverse in in Costa
Rica (only 1 genus)
-
Most adults are short-lived and do not have functional mouthparts
-
Immature stoneflies look very much like the adults with the exception of the wings, which are not present
in the nymph.
Example of Plecoptera immature
Order Hemiptera
Metamorphosis
Incomplete
Meaning of name
Hemiptera means "half wing" – part of the first pair of wings is
toughened and hard, while the rest of the first pair and the second
pair are membranous
Common names
True bugs
Mouthparts and feeding habits
Piercing/sucking mouthparts
Nearly all are predators of other aquatic organisms
Habitats
On the surface of fresh water, beneath surface, near shorelines
Identifying characteristics
-
Leathery forewing (hemelytra)
Mouth shaped like a sucking beak (proboscis)
Wings lie flat on the back at rest, forming an "X" or a triangle
Antennae slender with 4-5 segments
Facts about Hemiptera
- Water striders are common in quiet areas of rivers, lakes and ponds where they can be seen walking over
on the water surface. Water boatman are common in most water types. They range in size from 3 mm to
about one cm. Backswimmers are usually not as common but by no means rare. They are about one cm
long and have a distinctive keeled back and swim upside down.
- The immature stages and adults are very similar in structure except for the presence of wings in the
adult. However, some adult forms of the families Gerridae and Vellidae may be wingless.
- Some of the larger species such as the "giant water bug", Lethocerus americanus, will feed on small fish
and tadpoles. The forelegs in this creature are used to grasp the prey and the beak injects digestive juices
to kill the prey. The internal tissues of the prey are liquified by the digestive juices and sucked out.
- The life cycle of most water bugs involve over-wintering adults. Eggs are laid in the early spring and the
larvae develop through the summer months. Some, however, have over-wintering eggs.
- A number of hemipteran families, Gerridae, Microvellidae, and Mesovellidae are able to walk on the water
surface due to hydrofuge hairs on their legs that prevent them from breaking through the surface tension,
hence the common name of "water striders".
Water strider
Water boatman
Backswimmer
Giant water bug (Belastomatidae)
Order Megaloptera
Metamorphosis
Complete
Meaning of name
From the Greek word "neuron" meaning sinew and "ptera" meaning
wings. The modern English translation "nerve-wings" is appropriate
because of extensive branching in wing veins of most Neuroptera.
Common names
Two families: Corydalidae (Dobsonflies) and Sialidae (alderflies)
Mouthparts and feeding habits
Chewing mouthparts. Predators! (other insect larvae, crustaceans)
Habitats
Under stones or submerged vegetation
Identifying characteristics
Elongate, moderately flattened larvae
Lateral abdominal filaments
Anal prolegs (Corydalida) or caudal filament (Sialidae)
Some may have trachael gills (subfamily Corydalinae)
Examples of Megaloptera larvae
Order Coleoptera
Metamorphosis
Complete
Meaning of name
From the Greek words "koleos" meaning sheath and "ptera"
meaning wings, refers to the modified front wings which serve as
protective covers for the membranous hind wings
Common names
Beetles and weevils
Mouthparts and feeding habits
Strong mandibulate mouthparts; diets varied
Habitats
Varied – terrestrial, aquatic, burrowing, etc.
Identifying characteristics
Elytra!! – hardened forewings – defining characteristic
Front wings (elytra) are hard and serve as covers for the hind
wings; meet in a line down the middle of the back
Hind wings large, membranous, folded beneath the elytra
Chewing mouthparts (sometimes at tip of beak or snout)
Tarsi 2- to 5-segmented
Spanish name
Abejón (beetle)
Facts about Coleoptera
- Coleoptera is the largest and most diverse order in the class Insecta. Coleoptera is also the largest order
in the animal kingdom. It includes 40% of all insects and nearly 30% of all animal species.
- Beetle larvae often look very different from adults! Larvae are much more variable in form than adults.
Some have large fang-like mandibles others have chewing mouth parts. The legs can be reduced or well
developed. The abdomen can have lateral projections on it or dorsal ornamentation. Size can vary as
much as the size as the adult (2 mm to 3 cm)
- Of over 250,000 species of Coleoptera, about 5000 species have aquatic stages. Even so the beetles are
one of the most diverse freshwater macroinvertebrate groups.
- Coleoptera are found in all types of aquatic habitats but the diversity is highest in lentic (standing) water.
- The Gyrinidae, or “whirligig beetle,” is one of the most conspicuous and curious beetles. Adults are usually
seen in groups at the water surface swimming in a rapid and erratic manner. The adult eyes are divided
into upper and lower portions. This marvelous adaptation allows the beetles to live at the water surface
and be able to see above and below without any distortion caused by the air/water interface.
Whirlygig beetle larvae and adult
Halipidae larva and adult
Riffle beetle (Elmidae)
Order Diptera
Metamorphosis
Complete
Meaning of name
From the Greek words "di" meaning two and "ptera" meaning wings
– true flies have only a single pair of wings.
Common names
True flies – include mosquitoes, blackflies, crane flies, midges, etc.
Mouthparts and feeding habits
Sucking mouthparts – scavenger (dead organic matter), predators,
or parasites.
Immatures: Aquatic, semi-aquatic, or moist terrestrial. Found in
soil, plant/animal tissue, carrion/dung.
Habitats
Adults: wide range of habitats, enormous variation in appearance
and lifestyle.
Identifying characteristics
Facts about Diptera:
-
Mosquitoes (family Culicidae) are tolerant of standing water and can be harmful to humans and
livestock (bites, transmission of disease, etc.)
-
Blackflies (family Simuliidae) are the vector for river blindness. Larvae are filterers, are most commonly
found in flowing water, and have fans that they use to capture detritus. They are extremely common in
San Luis – they’re the ones that leave a small red dot when they bite you!
-
Some of the interesting adaptations flies have used to colonize the aquatic habitat include breathing
tubes, silken tunnels, and ventral suction cups.
Example of breathing tube, an adaptation for aquatic life & living in low-oxygen environments
Mosquito larva
Blackfly (Simuliidae) larva
Cranefly (Tipuliidae)
larva and adult
Midge (Chironomidae) larva
Order Trichoptera
Metamorphosis
Complete
Meaning of name
From Greek "trichos" = hair and "ptera" = wings, refers to the long,
silky hairs that cover most of the body and wings.
Common names
Caddisflies
Mouthparts and feeding habits
Herbivores, collectors, filterers, or predators
Habitats
Various habitats
Identifying characteristics
Caterpillar-like body; abdomen usually enclosed in a case made of
stones, leaves, twigs, or other natural materials.
Head capsule well-developed with chewing mouthparts
Thread-like abdominal gills usually present in case-makers
One pair of hooked prolegs often present at tip of abdomen
Facts about Trichoptera
-
Trichoptera are one of the most diverse orders of aquatic insects, with over 7,000 species worldwide.
-
Caddisfly larvae may serve as food for fish and other aquatic vertebrates. Fishermen often gather them
for use as bait for trout and other game fish.
-
Caddisflies are found in all types of aquatic habitats. The majority are intolerant of pollution and valuable
tools for monitoring organic and chemical contamination of habitats.
-
Females usually lay eggs directly into the water either singly or in masses. Some species lay their eggs
above the water on overhanging vegetation while those inhabiting temporary ponds lay their eggs in dry
pond basins.
-
The larval stage is the only real significant feeding stage. Most species are omnivorous. The larvae
scrape food off surfaces or shred decaying debris with their mandibles.
-
Caddisflies have diverse habitats and feeding behaviors. The majority fall into one of the following
groups:
(1) Case-building caddisflies build case of sand, small pebbles, leaves, or twigs. The case is held
together by silk produced by larvae and is used for camouflage and protection from predators.
(2) Net-spinning larvae produce silk and construct nets, which are used to trap detritus and other
organic matter from the water column. Caddisfly nets can be seen by looking closely at rocks in
streams.
(3) Free-living caddisflies do not construct nets, retreats, or cases.
Examples of caddisfly cases
Caddisfly cases with larvae
Example of a caddisfly