Common aquatic insects

March 4, 2012, 7:56 pm
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Image Source: Ken Billington

This article was researched and written by a student at Texas Tech University participating in the Encyclopedia of Earth's (EoE) Student Science Communication Project. The project encourages students in undergraduate and graduate programs to write about timely scientific issues under close faculty guidance. All articles have been reviewed by internal EoE editors, and by independent experts on each topic.

Introduction

Although there are almost no insect species in marine habitats, insects are among the most common and ecologically significant among the invertebrate macrofauna in freshwater habitats. There are 8 major orders of insects that spend at least a part of their lifecycle as a part of the freshwater ecosystem. Several of these orders are only aquatic during their larval stages, and only the aquatic stages of the lifecycle will be discussed here. Aquatic insects undergo both complete metamorphosis and incomplete metamorphosis, so the larvae stages can appear similar to the adults or they can look very different.

Aquatic insects have a variety of adaptations that allow them to successfully inhabit aquatic habitats. For more information about adaptations of stream insects see insect adaptations to stream systems.

For more information about these and other aquatic insects see Insecta (Aquatic).

Order Ephemeroptera

 

caption Mayfly larva of the order Ephemeroptera.

 

The larvae of mayflies are among the most common insect inhabitants of freshwater habitats, particularly streams. The larvae can be found throughout a diversity of habitats, more than any other aquatic insect order. However, most are found in lotic habitats (habitats with flowing water). Like many other stream insects, their bodies are dorso-ventrally flattened which allows them to remain in place in moving water. Mayfly larvae have a series of gills on the abdomen that takes the form of either a row of flat plates or a cluster of filaments depending on habitat that they use to pick up oxygen from the water..

Order Odonata

 

caption Dragonfly larva of the order Odonata.

 

The order Odonata includes the dragonflies and damselflies, the larvae of both groups being one of the prominent members of the macro invertebrate fauna in most freshwater systems. Like the mayflies, all members have an incomplete metamorphosis with aquatic nymph larvae and terrestrial, flying adults. As an order, most larvae superficially resemble wingless adults and are identifiable through the labium which can be folded over the mouthparts. Dragonfly larvae are often considerably stouter than damselfly larvae and damselfly larvae can be further identified through three gills that project from the rear of the abdomen. Almost all larvae from this order live in still water, lentic habitats such as ponds, bogs, and slow-moving streams. All dragonfly and damselfly larvae are active predators and are often the primary predators in the environments they inhabit. The labium is the primary instrument of prey capture. When not in use, it covers most of the face up to the eyes. During hunting, however, it is used as an instrument to grab prey and bring it to the mouth where it is either swallowed whole or sliced into manageable pieces. While damselfly larvae have three long external gills which are used to passively diffuse oxygen from the surrounding water (although they can wave them to create a current if there is none), dragonfly larvae house their gills in an abdominal chamber where water is constantly pumped over it. This chamber can also be used for locomotion, allowing dragonfly larvae to move by jet propulsion in short bursts if necessary.

Order Plecoptera

 

caption Stonefly larva of the order Plecoptera.

 

The larvae of plecopterans, or stoneflies, are one of the most common residents of stony, fast-moving, lotic environments; most commonly cool, small streams. They are therefore highly flattened and have long, filamentous, inarticulate gills. The entire order undergoes incomplete metamorphosis, with aquatic larvae and terrestrial adults.

Order Hemiptera

 

caption Water bug (Photograph by Arjun Rajagopalan)

 

There is only one suborder of true bugs that makes an appearance in the invertebrate megafauna of aquatic systems. Aside from the Heteropterans no other members of the order can be found in aquatic habitats at any point in their lifecycle. Also, unlike the aforementioned orders, all aquatic members of the order Hemiptera are aquatic throughout their lifecycle. The most famous aquatic representatives of the order are the water striders, water bugs, and water boatmen. Members of the order are found exclusively in lentic habitats, requiring still or entirely still water for survival. Alongside dragonfly and damselfly larvae, water bugs are the primary invertebrate predators of still-water environments. Like other hemipterans, the mouthparts of water bugs are modified into a piercing, sucking mechanism used to dissolve the insides of prey and suck the meal out as a fluid. Water Bugs have no gills, and depend on surface air for gas exchange. Several species carry bubbles of surface air with them below water as a consistent, portable air supply.

Order Megaloptera

 

caption Dobsonfly larva of the order Megaloptera.

 

The order megaloptera (dobsonflies) is small, containing only two families, the larvae of both of which are prominent in freshwater environments. They undergo complete metamorphosis, with the larvae being aquatic and the adults and pupae terrestrial in all habitats. The larvae of all species are elongate, wormlike, and dorsoventrally flattened. The body is soft and fleshy with several protruding filamentous gills along the abdomen. The most notable feature, however is the head which has thick, hard skin and a pair of prominent biting chewing mouthparts that make the larvae, commonly called “hellgrammites”, one of the most impressive members of the invertebrate macrofauna. Larvae of most species live in silty pool areas of lotic stream habitats where they spend most of their lives as burrowers. They are active predators, taking whatever prey they can catch and consume, and are among the most important predators in stream systems. Gas exchange takes place for the most part across the soft, fleshy tissue on the abdomen of their body.

Order Coleoptera

 

caption Diving beetle of the order Coleptera.

 

The beetles are the largest order of insects, with over 100 species and more than 24,000 species in North America alone. As one of the most successful orders of insects, beetles have found a niche within aquatic habitats as well as the diversity of other environments they inhabit. Water Beetles undergo a complete metamorphosis, and adults and larvae nymphs both inhabit the same habitats. Adults resemble other beetles largely. The larvae are elongated with a hard head, a large, filamentous gill protruding from the end of the abdomen, and a fleshy body. Although most water beetle species are most common in still water, they can be found in most freshwater environments. There is no method of feeding or locomotion that can categorize all, or even most water beetle species, and their diversity of niches within aquatic habitats is almost as great as the diversity of the order Coleoptera itself. Larvae have a closed respiratory system, diffusing water through the use of filamentous gills or across the soft body membrane. Adults, however, much like water bugs mentioned previously, have an open system and must collect surface air in pockets underneath the hard outer wings in order to breathe. In which the adults rarely ever have to come to the surface to breathe. However, these beetles require massive amounts of oxygen and can only be found in frigid, highly lotic waters, where oxygen is near a saturation point. The water pennies (family Psephenidae) are also unusual in that while the larvae are highly adapted for stony areas with fast water currents, the adults are entirely terrestrial, making them the only aquatic beetle species in which the adults and larvae do not share a habitat.

Order Trichoptera

 

caption Andamen Islands, India. (Photograph by Arjun Rajagopalan)

 

The larvae of the caddisflies are most renowned for the silk “houses” they build. The larvae can be found in most aquatic habitats, and they undergo complete metamorphosis with aquatic larvae and terrestrial adults. The larvae are vermiform (worm-like) and capable of spinning silk, which they use to build shelters and anchor themselves to the substrate. Several species also use silk in filter feeding behavior, which is one of the most common feeding methods (although other feeding methods are represented.) They have a closed circulatory system, and use their silk for gas exchange as well, wiggling their bodies within their case to create a constant current over their soft body to allow diffusion to take place.

Order Diptera

 

caption Mosquito larva of the order Diptera. (Source: Landcare Research)

 

The final insect order worthy of note in aquatic habitats are the true flies, which include the mosquitoes, midges, and blackflies. All dipterans undergo complete metamorphosis, and in aquatic species, it is only the larvae that are aquatic. All dipteran larvae are vermiform, and soft-bodied, however, similarities end there among most species. Most aquatic dipteran larvae are the most adaptable of aquatic insects and can be found in stagnant, or often disturbed or anoxic environments. Certain members of the order can even be found in habitats as harsh as coastal tide pools where they provide the only insect representatives. Several among the most famous members of the order are filter feeders, however most species are collector-gatherers, and there are even a few predators. The breathing methods are also diverse, however most are adapted for low oxygen habitats. Mosquitoes obtain oxygen through an abdominal tube which is kept above the surface of the water. Some species of Midges have hemoglobin in their blood, allowing them to live in habitats with minimal amounts of dissolved oxygen.

 

What do they look like as adults?

Many of the insects described above are aquatic as larvae and then live in the terrestrial environment as adults (they show an ontogenetic niche shift).

Epemeroptera (mayflies)

caption Andamen Islands, India. (Photograph by Arjun Rajagopalan)

Odonata (dragonflies and damselflies)

Plecoptera (stoneflies)

Megaloptera (dobsonflies)

Trichoptera (caddisflies)

Diptera (true flies)

References and Further Reading

  • Cummins, Kenneth W., Merritt, Richard W., 1978. An introduction to the Aquatic Insects of North America. Kendal/Hunt. Iowa.
  • Environmental Interpretation Center. Identifying aquatic insects. Environmental Interpretation Center, University of Michigan, Dearbon.
  • Huryn, Alexander D., Wallace, Bruce J., 2000. Life History and Production of Stream Insects. Annual Review of Entomology.
  • Hynes, H.B.N., 1970. The Ecology of Running Waters. University of Toronto Press. Toronto.
  • Hynes, H.B.N., 1970. The Ecology of Stream Insects. Annual Review of Entomology
  • Macan, T.T., 1962. Ecology of Aquatic Insects. Annual Review of Entomology.
  • Merritt, Richard W., Wallace, Bruce J., 1980. Filter Feeding Ecology of Aquatic Insects. Annual Review of Entomology.
  • Penobscot County Soil & Water Conservation District. Identifying aquatic insects from your pond Penobscot County Soil & Water Conservation District, Natural Resources Conservation Service.
  • The Connecticut River Homepage. Some general information about North American aquatic insects. Biology Department, University of Massachusetts at Amherst.
  • U.S. Environmental Protection Agency. Life cycle of aquatic insects.
  • Voshell, Reese Jr., 2002. A Guide to Common Freshwater Invertebrates of North America. McDonald & Woodward Publishing Company. Virginia.
Glossary

Citation

Singletary, E. (2012). Common aquatic insects. Retrieved from http://www.eoearth.org/view/article/151318

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