Aquatic Invertebrates

(Craneflies, Blackflies, Stoneflies, Aquatic Earthworms)






(Simuliidae) 2


(Plecoptera) 3


Aquatic Earthworm

(Oligochaete) 4




Life in Emigration Creek
Food Chain of Aquatic Invertebrates
What are Craneflies?
Characteristics of Blackflies
History of Stoneflies
Characteristics of Aquatic Earthworms


Emigration Creek

        Cold and constant, the waters of Emigration Creek are, at first glance, barren of life. Too fast for frogs, its piped waters are too manhandled to accommodate fish. Inspect a wayside rock and  water moss can be seen, clinging to a rock - the seemingly sole resident of the fast flowing creek. Enter magnification. With a trusty stereoscope in hand, one can find a myriad of life teaming within the waters of the creek. The right sample cup can provide a number of different craneflies, blackflies, stoneflies, and aquatic worms.


Food Chain of Aquatic Invertebrates


Emigration creek contains a food chain of small proportions. Leeches being the highest found on the underwater food chain, while bacteria places lowest.           





There are over 200 species of craneflies and over 1500 of them live in North America. Craneflies are insects and - like all insects - they have six legs. Craneflies have one set of wings, unlike dragon flies. Craneflies are usually brown or grey, some have dark markings on their wings. Craneflies have big compound eyes, small short antennae and small structures on their sides called halteres.  Craneflies are common near water where vegetation is plentiful. Often times they are mistaken for giant mosquitoes, but they really don't bite at all. Most craneflies grow to 10mm.-25mm. long.  Craneflies belong in the class Insecta, the order Diptera, and several families including tipulidae.

This is the largest family of flies. Their larvae may be aquatic or live in moist soil or decaying vegetation. The larvae may feed on plants, fungi, decaying vegetation or be predatory on small animals. The adults of this family are sometimes called "mosquito hawks" in the mistaken belief that they may attack mosquitoes or other small flies. In fact, they may not feed at all as adults.


Females deposit eggs on submerged vegetation or other debris. Larvae are definitely "worm-like"; thick-skinned, and brownish-green to somewhat transparent or whitish; pointed or rounded at one end and a set of disk-like spiracles at the other; color may be stained greenish or brownish; length up to 3 inches.


Craneflies feed mostly on plants and plant debris; some are predaceous.




Black flies, also known as buffalo gnats and turkey gnats, are small, bloodsucking insects slightly less than 1/4 inch long with a stout-body and hump-backed appearance. They are most common along rivers and streams during late spring and early summer.

Only the female black flies are bloodsuckers. Their bite is extremely painful, and the injection of a venom into the skin causes intense itching, local swelling and soreness. All exposed parts of the body are subject to attack, tough they favor the head, just beneath the hat rim.

Severe complications (swelling) from black fly bites are possible in allergic individuals and rare cases of death from toxemia or anaphylactic shock have been reported. In the United States, black flies are not known to transmit diseases to humans. Livestock, pets, poultry and wildlife are also severely irritated by these flies.

Black flies live as larvae in shallow, clear, fast-running water in rivers and streams. The black, spindle-shaped larvae live on the river bottom attached to rocks and other submerged objects and feed on tiny bits of organic matter, algae and protozoa. Larvae transform in the water to adult flies that rise to the water surface in a bubble of gas. The adult flies are usually present for about 3 weeks before they die.

Blackfly larvae cover roots and stones by using a hook-like appendage found on their tail  to cling tightly.  They eat materials filtered from sweeping the water that passes by. 



Life History

The stoneflies are terrestrial as adults, but in the nymphal stages they are strictly aquatic, and most are restricted to flowing waters of relatively high oxygen concentrations. Fertile eggs, laid over or in the water, require two to three weeks for hatching in many species, and several months among some larger forms. Adults live from 1 to 4 weeks. Most adults are winged, although a few species are wingless (apterous) or have short wings (brachypterous). None fly well and this has prevented them from crossing even small geographical barriers.

Temperate species that over winter as nymphs often do not stop growing even in water temperatures close to 0C. It seems that it is warm water temperatures rather than cold ones that punctuate stonefly life cycles.

Habitat and Ecological preference

Plecopteran nymphs are restricted to cool, clean streams with high dissolved oxygen content. some species, however, may be found along the wave-swept shores of large oligotrophic lakes. When subjected to low dissolved oxygen concentration, the nymphs o f many species exhibit a characteristic "push-up" behavior that increases the rate of movement past the gills. The gills are variously placed among species on the neck, thorax and abdomen. However, some species have no gills and respiration in these is a assumed to be across the cuticle surface.

Field surveys clearly show that the nymphs of many species are associated with particular sections of a stream bed or lake shore. The specific microhabitat occupied depends on a variety of environmental factors such as the nature of the substratum (particle size and configuration), current regime, presence of other organisms, and local variations in water chemistry and temperature. Habitat preference often changes as the nymphs develop and with season.

Most stoneflies are classified as clingers or sprawlers, as they are closely associated with the substrate or leaf litter. A few species have been reported from the hyporheic zone.


Generally, stonefly nymphs are either shredders or predators. Some groups that are predaceous as late instars have been reported to be herbivorous or detritivorous in early instars, while late instars of large detritivores may consume some prey. Predators are engulfers, that is, they swallow their prey whole or bite off and swallow parts of prey. They are active search or pursuit predators, using their long filamentous antennae to locate prey using tactile, wave disturbance, and chemical cues. Many species are opportunistic feeders, consuming prey in proportion to their relative abundance. Other species are selective for prey species or sizes. In some families adults feed, and in others they do not.

Some stoneflies are carnivorous, others feed on algae, bacteria, and vegetable debris; eaten by a variety of fish species


Aquatic Earthworms


Many aquatic worms look similar to earthworms. In streams, you may also find very long, slender worms (such as horsehair worms), or flatworms, like planaria, which are small, sticky and soft-bodied. These worms will typically "wiggle" in a snake-like fashion. Colors vary greatly in this category (red, white, brown are common). Worms do not have legs.

Key Features:

    - no legs

    - smooth coat

    - may be round or flat

    - size range: 1/4" -5"


Aquatic Earthworms reproduce hermaphrodidically, similar to earth worms; fertilization and development of embryos occur in a cocoon.


Like earth worms, they ingest large quantities of mud and filter out organic debris; they also fed upon by bottom feeders or fish.

Ecological Role

Aquatic oligochaetes are generally found in soft mud bottoms, and in high numbers are considered indicators of very poor water quality.


Graph of Emigration Creek





Segmented worms:

American Stonefly Webpage:

Stonefies of the United States:


EPA- worms:

Aquatic worms:

Nedham and Nedham, 1966.   A Guide to the Study of Fresh Water Biology, Holden Day and Company, San Francisco.

Pennack, 1989.   Freshwater Invertebrates of the United States , John Willey and Sons and Company,  New York.  

Lehmkuhl,  1979.  How to Know the Aquatic Insects , WCB McGraw Hill. Boston.

McCafferty, 1981.  Aquatic Entomology, Jones and Bartlet Publishers.  Boston.

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