Illinois Digital Archives
There are hundreds of aquatic macroinvertebrate species in Illinois. Generally, they can
be grouped into the following categories: sponges; hydrazoans; flatworms; aquatic
nematodes; horsehair worms; aquatic earthworms; leeches; bryozoans; snails; mussels and
clams; and arthropods. These organisms exhibit a variety of adaptations to help them survive
in water. Although too numerous to list all of them here, some examples of these adaptations
are described below.
Breathing – All aquatic invertebrates must have oxygen for respiration and remove carbon
dioxide from their body. Many of them come to the water’s surface to obtain air. They can trap
it by using body parts (wings, legs, hairs) or gulp it through breathing tubes. Water contains
dissolved oxygen. Some aquatic macroinvertebrates take advantage of dissolved oxygen with
their internal or external gills, by absorption directly through the skin or by using a bubble of
air that was trapped at the surface and attached to their body. The bubble can extract oxygen
from the water.
Feeding – Some species are able to filter small organisms and other food particles from the
water. Other species hunt prey, eat plants or scavenge.
Protection – A physical barrier, like a protective shell or a case built of stones, sand or plant
material, can be used to help escape predation. Behavioral adaptations (fleeing, burrowing or
hiding) also are effective. Coloration that blends with the surroundings affords protection as
Locomotion – For moving in the water column, swimming is often accomplished with the aid
of paddlelike appendages. The bottom-dwelling macroinvertebrates may crawl or burrow. Some
burrowing species have legs shaped like shovels. Claws are present on some bottom-dwellers
where the current is strong. They must cling tightly to objects on the bottom to keep from
being swept away. Suckers are used by leeches to hold on to the substrate and to move. Other
macroinvertebrates use the surface tension of the water as a base for them to glide or walk upon.
Life Cycle – Some aquatic macroinvertebrates (aquatic worms, mollusks, most crustaceans)
spend their entire life in water. Others use water for a portion of their life cycle (many insects)
or as a base from which they can go to other moist habitats (crayfish).
Reproduction – Crayfish lay their eggs in water, and the eggs and young develop there. Adults
may move to other moist habitats. Most water fleas (crustaceans) reproduce parthenogenically,
eggs develop without being fertilized by a male, hatch internally and are born live. Males are
occasionally produced, and they mate with females to form cysts that can live in a dormant
state for years. Most snails are hermaphrodites, with both male and female reproductive systems.
Although they do not fertilize their own eggs, in these species any two snails can mate. Insects
use a variety of reproductive strategies.
Dispersal – Many aquatic insect adults can fly. Moving to a new area is simple for them.
Crayfish are capable of leaving water to travel across land. The adult stage of some insects may
be terrestrial. Flooding can help to disperse species. Ducks, geese and other waterfowl and
wading birds may inadvertently take along eggs of aquatic macroinvertebrates on their feet as
they move to a different location. The stream current is an effective means of transportation.
carnivorous feeding on the flesh of other organisms
detritivore organism that eats detritus
detritus organic matter on the bottom of a body of water
macroinvertebrate animal that can be seen without magnification and that has no
mandible one of a pair of insect mouthparts located directly behind the
membranous made of a thin tissue
omnivore organism that obtains and eats both plant and animal materials
periphyton plants that grow on or from the bottom of a water body
phytoplankton tiny organisms that float in the water column and are capable of
making their own food
plankton microscopic organisms suspended in the water
plastron thin film of air held to an insect’s body by hairs or scales
predaceous feeding on organisms (prey) that the animal (predator) has hunted
prehensile adapted for grasping
rostrum in insects, a beaklike process
semiaquatic living in an environment that is associated with an aquatic
environment or living in a wet environment
silty covered with dirt, fine sand or other very tiny particles that have
been carried and deposited by water
spring a place where groundwater exits onto the earth’s surface
terrestrial living on land
transformation change in form, such as from an immature to the adult
Cummings, K. S., and C. A. Mayer. 1992. Field guide to freshwater mussels of the Midwest.
Illinois Natural History Survey Manual 5. 194 pp.
Huggins, D. G., P. M. Liechti, and L. C. Ferrington, Jr. 1985. Guide to the freshwater
invertebrates of the Midwest. Technical Publication 11. Technical Publications of the
Kansas Biological Survey, The University of Kansas, Lawrence, Kansas. 221 pp.
Illinois Department of Natural Resources. 2003. Aquatic Illinois CD-ROM. Illinois
Department of Natural Resources, Springfield, Illinois.
Illinois Department of Natural Resources. 2008. Stream monitoring.
http://www.dnr.state.il.us/education/EcoWatchFiles/mainpage.htm. Illinois Department
of Natural Resources, Springfield, Illinois.
Jeffords, M. R. 1997. Aquatic invertebrates in still and flowing waters poster and activity.
Illinois Natural History Survey, Champaign, Illinois.
McCafferty, W. P. 1981. Aquatic entomology. The fishermen’s and ecologists’ illustrated guide
to insects and their relatives. Jones and Bartlett Publishers, Boston, Massachusetts. 448 pp.
Merritt, R. W., K. W. Cummins, and M. B. Berg. 2008. An introduction to the aquatic
insects of North America. Kendall Hunt Publishing, Dubuque, Iowa. 1158 pp.
Smith, D. G. 2001. Pennak’s freshwater invertebrates of the United States. 4th edition.
Wiley & Sons, New York, New York. 648 pp.
Thorp, J. H., and A. P. Covich. 2001. Ecology and classification of North American
freshwater invertebrates. Second edition. Academic Press, San Diego, California. 950 pp.
Voshell, J. R., Jr. 2002. A guide to common freshwater invertebrates of North America.
The McDonald and Woodward Publishing Company, Blacksburg, Virginia. 456 pp.
aquatic mite Order Prostigmata
Water mites are common year-round in aquatic habitats throughout Illinois. Ranging from
transparent to blue, green, red and other colors, these animals are often conspicuous in a variety
of habitats.Water mites seen swimming freely are adults. Immature individuals seek out various
insect hosts, including beetles, true bugs, stoneflies, true flies and dragonflies. Immature water
mites attach themselves to membranous portions of the aquatic insect and remain attached
until maturation. Upon transformation, the mite becomes free-living. The free-living stage is
typically carnivorous, feeding on aquatic insects, small crustaceans and aquatic worms. A few
species are omnivores, feeding on vegetation and detritus as well.
aquatic snail Pleurocera acutum
Snails are univalves, having a single shell with a spiral, coil or cone. Aquatic snails range from
about one-eighth inch to about three inches in length. The head has a pair of tentacles.
Aquatic snails crawl on the bottom of nearly all freshwater aquatic habitats but prefer the
shallow areas with little water movement and many plants. Snails require calcium carbonate to
produce their shell, so aquatic snails are more common in water with abundant supplies of
calcium carbonate. Some of these creatures are detritivores or omnivores while others feed on
algae. Snails are an important food source for many other aquatic species.
aquatic sowbug Asellus sp.
Aquatic sowbugs are found in a variety of aquatic habitats in Illinois, often living among leaf
litter and detritus. They are particularly abundant in springs. A few species are predaceous
but most are omnivore-detritivores, feeding on a variety of food sources.
aquatic worm Slavina appendiculata
This species, a segmented worm, is widely distributed throughout Illinois. It is free-living and
found in detritus mats, in silty substrates and other debris in lakes, ponds, streams and rivers.
It is a detritivore, feeding on periphyton and phytoplankton.
backswimmer Notonecta irrorata
The backswimmer is a common sight in Illinois ponds, lakes and sometimes in swimming pools
and other nonnative habitats. It is a predator and supreme swimmer. Its formidable “beak,” or
rostrum, that appears as a large needle, is a piercing-sucking device for capturing prey and
feeding. Backswimmers make a migratory flight in autumn to suitable habitats for reproducing
and overwintering. They are active year round under water, even under ice in winter.
devil crayfish Cambarus diogenes
The devil crayfish can be found statewide in Illinois. It is one of four species in the state that
spends a majority of its time in underground burrows that it builds. Burrows are often located
along creek and lake margins and usually have a mud chimney. Devil crayfish consume insects
and plant matter as the main components of their diet.
dobsonfly Corydalus sp.
Dobsonfly adults are attracted to lights and may be seen flying around street lights on summer
evenings. Males and females can be easily distinguished, as females have short, functional
mouthparts, while males have very long (several times longer than the head) mandibles that
are used for courtship, defense and aggressive behavior. Dobsonfly males are a formidable
sight when encountered. Larvae, called hellgrammites, are used by humans as fishing bait.
Larvae have well-developed gills for underwater respiration. Larvae can attain a length of
about three and a half inches, while adults can be more than six inches long, including the
wing length. Since the larvae require well-oxygenated water conditions, when present, they
are indicative of good stream or river quality.
dragonflies and damselflies Aeshna sp., Libellula sp. and
Dragonfly and damselfly adults are familiar sights in Illinois, especially in the spring and
autumn. Adults are entirely terrestrial and are active predators on mosquitoes and other
insects. Immature dragonflies and damselflies are less conspicuous but inhabit all aquatic
habitats in Illinois. Just like the adults, nymphs are voracious and opportunistic predators,
often feeding on organisms much larger than themselves. The mouthparts of dragonfly and
damselfly nymphs are modified into an extensible prehensile structure. It is retracted under
the head at rest, and when feeding, the animal rapidly shoots out the mouthparts to capture
prey. Dragonfly nymphs are excellent swimmers and can use “jet propulsion” under water by
forcefully expelling water from their abdomen to move from place to place.
fishing spider Dolomedes sp.
Several species of spiders occur on the shoreline of lakes and ponds and on the banks of rivers
and streams. All are predaceous, feeding generally on aquatic and semiaquatic organisms.
Fishing spiders do not spin webs but actively hunt their prey on the water’s surface. They dive
below the water to prey on submerged organisms or to escape predation. They can remain
submerged for several minutes and use a large air bubble attached to their body (plastron) to
breathe. These spiders are common throughout Illinois.
giant water bug Belostoma lutarium
Giant water bugs are large. They are known as “electric light bugs” because they were once
commonly seen around street lamps and other lights, especially in the spring and autumn.
Giant water bugs are strong flyers and occur in many aquatic habitats across Illinois. Nymphs
and adults are predators, feeding on aquatic insects and other macroinvertebrates their own
size, small fishes, tadpoles, frogs, salamanders and even other giant water bugs.
leech Class Hirudinea
Leeches are segmented worms. Their body is flattened and has 34 segments. They may be
brightly colored or have a distinctive pattern, although usually their background color is
some shade of brown, gray or black. The underside of the body has a sucker at each end, with
the mouth contained in the anterior sucker. Suckers are used for feeding, movement and
attachment. Some leeches live freely, feeding on organic materials on the bottom of the water
body or preying upon invertebrates, including leeches. Other leeches are external parasites on
vertebrates, such as fishes and amphibians. Leeches are usually found in quiet water that is less
than six feet deep and that has an abundance of protective cover (plants, plant parts, rocks).
They range in size from about one-fourth inch to several inches long.
mayflies Hexagenia sp. and Isonychia sp.
Mayflies are common and frequently abundant in Illinois. They have a very short life span
(often two weeks or less). Nymphs of Illinois mayflies are aquatic, while adults spend their
short life out of the water. Mayflies occur in a variety of aquatic habitats and specialized
niches. Some mayflies are excellent swimmers, some are effective burrowers and others sprawl
on rocks within streams and rivers. Immature mayflies are extremely sensitive to changes in
environmental conditions and are excellent indicators of stream and river habitat “health.”
monkeyface mussel Quadrula metanevra
The monkeyface mussel lives in medium or large rivers with a gravel or sand-and-gravel bottom.
The common name of this species results from an indentation on the posterior edge of the
shell that has the appearance of a chimpanzee. Growing to four inches in length, the shell is
rounded or square with large bumps on the posterior section. There may be zigzag marks on
the shell. Mussels have a complicated life cycle that involves a host for its parasitic intermediate
larval stage, the glochidium. Food for mussels consists of detritus and plankton that they filter
from the water.
mosquito Toxorhynchites sp.
Mosquito larvae are aquatic and occur anywhere there is standing water: lakes; ponds;
swamps; marshes; bogs; tree holes; pitcher plant leaves; old tires; buckets; ditches; and any
other depression that will hold water for a short time. Larval mosquitoes remain near the
water’s surface to utilize atmospheric air by means of a respiratory siphon. Some mosquitoes
can remain submerged by tapping their air siphon into plant tissue or roots for oxygen. Most
larvae are detritivores, however some are omnivorous and predatory, feeding on smaller
aquatic organisms. Larval mosquitoes are called “wrigglers” because of their thrashing and
diving motions when disturbed. Mosquito pupae generally remain near the surface of the
water, where they molt to the adult mosquito, finishing the complete metamorphosis cycle.
Female mosquitoes eat blood, while males feed on plant sap.
northern clearwater crayfish Orconectes propinquus
The northern clearwater crayfish is commonly found in rocky areas of creeks and lakes in the
northern two-thirds of the state. It eats aquatic insects, algae, fishes and, in some cases, other
crayfish. This species is being displaced in many regions of its range by the invasive rusty
crayfish, Orconectes rusticus.
predaceous diving beetle Dytiscus circumcinctus
Predaceous diving beetles range in size from about the width of a ball-point pen tip to nearly
two and a half inches. Larvae and adults are predators. The larvae are called “water tigers”
because of their active hunting habits. Larvae and adults are known to prey on small fishes,
tadpoles, frogs and other aquatic beetles. Adults and most larvae must rise to the surface peri-odically
to renew air stores for breathing. This family of beetles is found statewide in Illinois.
They are often the first beetles to colonize a temporary or new aquatic habitat.
pygmy backswimmer Neoplea striola
Pygmy backswimmers are common although often overlooked due to their small size.
They are widely distributed and often occur in very large populations, sometimes associated
with a hatch of their potential prey items, including mosquito larvae and other aquatic
macroinvertebrates. Pygmy backswimmers swim upside down but are not great swimmers.
They move freely throughout the water column, sometimes attaching to aquatic vegetation.
water boatman Trichocorixa calva
Water boatmen are most abundant during the spring and autumn. Both nymphs and adults
spend their entire life in water except when adults disperse to new habitats. Water boatmen
are omnivorous, with most Illinois species feeding on plant and detritus material while a few
species are predaceous. Unlike all other true bugs, water boatmen lack a true beak (rostrum),
or piercing-sucking mouthparts. Found throughout Illinois, water boatmen are an important
food source for wading birds, shorebirds, ducks, geese and other animals associated with
Illinois aquatic habitats.
water scavenger beetle Hydrochara sp.
Water scavenger beetles are found throughout Illinois aquatic habitats. They vary in size from
extremely tiny to about two and a half inches in length. Some members of this family are more
terrestrial than aquatic. Adults may be omnivores-detritivores or predatory. Larvae of aquatic
species are typically predatory. Water scavengers breathe air and must surface to renew air
supplies. These beetles are often found in association with predaceous diving beetles, usually
in very large numbers.
The Illinois Department of Natural Resources (IDNR) and other institutions in the state offer
additional information about aquatic macroinvertebrates. The IDNR Division of Education
has many Illinois-specific resources related to aquatics and aquatic macroinvertebrates for
teachers. See the Web address listed below for more information. Publications about
aquatic macroinvertebrates can be ordered through the Publications page at
http://dnr.state.il.us/teachkids. The Illinois Natural History Survey in Champaign and
the Illinois State Museum in Springfield have significant collections and conduct studies
of aquatic macroinvertebrates. The Illinois Wildlife Preservation Fund, comprised of
taxpayer donations, helps to support further understanding of these creatures by providing
grants for projects, such as the development of this poster.
Illinois Department of
Division of Education
One Natural Resources Way
Springfield, IL 62702-1271
Illinois Department of
Illinois State Museum
502 South Spring Street
Springfield, IL 62706
Illinois Natural History Survey
1816 South Oak Street
Champaign, IL 61820
Equal opportunity to participate in programs of the Illinois Department of Natural Resources (IDNR) and those funded by the U.S. Fish and
Wildlife Service and other agencies is available to all individuals regardless of race, sex, national origin, disability, age, religion or other
non-merit factors. If you believe you have been discriminated against, contact the funding source’s civil rights office and/or the Equal
Employment Opportunity Officer, IDNR, One Natural Resources Way, Springfield, IL 62702-1271; 217/785-0067; TTY 217/782-9175. This
information may be provided in an alternative format if required. Contact the DNR Clearinghouse at 217/782-7498 for assistance.
Printed by the authority of the State of Illinois 10M - 6/09 IOCI 1198-09
Illinois Aquatic Macroinvertebrates © 2009, Illinois Department of Natural Resources
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