Chironomidae

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Diversity

The Chironomidae is a large and diverse family of flies. They are commonly known as "non-biting midges." There are over 20,000 species known world-wide, including 2,000 in the Nearctic. Adult midges are relatively small (1-20 mm long), with narrow bodies and long legs. They are often confused with mosquitos, but no members of this family are blood-feeders (hence the "non-biting" part of the common name). Adults, if they feed at all, feed on nectar or similar substances. Midge larvae are nearly all aquatic or sub-aquatic, and are a very important part of many freshwater ecosystems. Both in numbers and in diversity, they are often the largest group of primary consumers in these systems. Species of Chironomidae can be found in an enormous variety of aquatic habitats, from brackish estuaries to pools in tree-holes, and from low-oxygen lake sediments to fast-flowing mountain streams. (Coffman and Ferrington Jr., 1996; Foote, 1987; McCafferty, 1983)

Geographic Range

Species of chironomid midges are found in moist or wet habitats in all major landmasses of the world, including Antarctica, and most islands. (Foote, 1987)

Habitat

Midge larvae occur in all kinds of benthic freshwater habitats, including the bottoms of streams, rivers, lakes, ponds, and temporary pools, also wetlands such as marshes and swamps. Some breed in isolated damp habitats such as tree-holes, pitcher plants, patches of moist soil, even dung pats. The "blood midges" or "bloodworms" are species of midges with hemoglobin in their hemolymph, which allows them to survive in low-oxygen (and often heavily-polluted) habitats. Adults rarely disperse far from the larval habitat. (Coffman and Ferrington Jr., 1996; Foote, 1987)

Physical Description

Adults are small (1-20 mm long, most less than 10 mm), slim, long-legged flies. They resemble, and are often confused with, mosquitoes (Culicidae), but unlike mosquitoes, they do not bite, and have no scales on their wings. Many species rest on their hind two pairs of legs, and hold their forelegs out in front of them. In most species, adult males have plumose antennae that are much larger than the females (these are probably used to locate females). Most species are dark-colored, usually brown or black.

Larvae are elongate and cylindrical, with distinct segmentation and a hard sclerotized head capsule that cannot be retracted into the body. They have no true legs, but do have a pair of unjointed "prolegs" on the first segment of the thorax. The presences of this pair of prolegs, the absence of true legs, and the structure of the head are good distinguishing marks for identifying larvae in the Chironomidae. Color varies widely among larvae, most are tan or brown, but some are whitish, some are green. Larvae of a number of species in the subfamily Chironominae have the hemoglobin in their circulatory fluid, which helps them survive in low-oxygen habitats. These larvae are pinkish or red when alive, and are often called "blood midges." (Coffman and Ferrington Jr., 1996; Foote, 1987)

  • Sexual Dimorphism
  • sexes shaped differently

Development

Like all flies, the Chironomidae are holometabolous, and undergo metamorphosis in their life cycle. Adult females lay eggs in aquatic habitats. The larvae that hatch from these are often planktonic in their first instar, floating in the water column and feeding on microscopic particles in the water. After their first molt, larvae of most species descend to the bottom and remain benthic through the rest of the larval stage (usually four instars). The larvae transforms into a pupa, which often stays within a shelter or cocoon while it transforms into an adult. When it's time to emerge, the pupa swims to the surface, and the adult pulls itself out of its old skin. (Coffman and Ferrington Jr., 1996; Foote, 1987; McCafferty, 1983)

Reproduction

Adult non-biting midges often form mating swarms, either in the air near oviposition sites, or "skating" on the surface of water. These swarms are composed mostly of males, and may serve to attract females. (Coffman and Ferrington Jr., 1996; Foote, 1987; McCafferty, 1983)

In most species, eggs are laid in gelatinous masses on the water surface or on emergent vegetation. In some species, females lay their eggs in or under the water. Adult chironomids usually only live for a few days or weeks, and so reproduction is a single concerted effort. Most species breed seasonally. A very few species are reported to be parthenogenic, most have male and female adults (Coffman and Ferrington Jr., 1996; Foote, 1987)

No male investment. Female investment is in provisioning eggs and producing a protective gel mass for them. (Coffman and Ferrington Jr., 1996)

  • Parental Investment
  • pre-fertilization
    • provisioning

Lifespan/Longevity

Lifespan varies greatly between and within species in the Chironomidae. Individual growth and development rates are strongly influenced by temperature and other environmental factors. Many temperate species live for a year, surviving the winter as larvae. Some species are known to complete entire life-cycles in a few weeks, if temperatures are warm and food is abundant. (Coffman and Ferrington Jr., 1996; Foote, 1987)

Behavior

Larvae of non-biting midges are often found in enormous numbers, but this may reflect individuals choosing the same microhabitat rather than social interactions. Most species that live in mud or silt or other soft sediments build tubes or tunnels as refuges.

Some larvae are planktonic when in the first instar, then become benthic after they molt. In cold climates, larvae over-winter in cocoons in the sediment where they live. Pupae also generally stay in place, hidden in sediment. They only emerge to swim to the surface. Adult males gather in swarms, in daylight or twilight, sometimes in many thousands. They often gather over a local prominence -- a tall tree or a rock outcrop or a hill top.

Larvae are most active in the dark. (Coffman and Ferrington Jr., 1996; Foote, 1987; McCafferty, 1983)

Food Habits

The many thousands of chironomid species have many different feeding habits. Most species feed on small particles of organic debris, but the size of particles varies, some shred bits of dead wood and leaves, some gather smaller particles, some even filter tiny particles suspended in the water. Some of these detritivores also collect algae cells, and some species are herbivores, specialize in feeding on algae. Other herbivores are "miners" tunneling in larger vascular plants. There are some fungivore chironomids as well, eating spores and grazing on hyphae. A few species are simple predators, often attacking other chironomid species. (Coffman and Ferrington Jr., 1996)

Predation

Non-biting midges are so abundant in so many freshwater habitats that practically every kind of predator in these habitats feeds on them at some stage of their life cycle. Midges try to avoid predation by limiting their activity during daylight, and larvae and pupae take refuge in tunnels that they build in sediment. Many species are cryptically colored. (Coffman and Ferrington Jr., 1996; McCafferty, 1983)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Chironomids are the most diverse and abundant macroinvertebrates in most of the aquatic ecosystems they inhabit (and they inhabit most aquatic ecosystems). Most natural ponds, lakes and streams are home to 50-100 different species of non-biting midges. Collectively, they play a vital role in freshwater ecosystems as primary consumers. They harvest an enormous amount of energy from detritus and are one of the major supports for animal communities in these systems. (Coffman and Ferrington Jr., 1996)

Contributors

George Hammond (author), Animal Diversity Web.

Glossary

Antarctica

lives on Antarctica, the southernmost continent which sits astride the southern pole.

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

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Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

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Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

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Neotropical

living in the southern part of the New World. In other words, Central and South America.

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Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

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benthic

Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

bog

a wetland area rich in accumulated plant material and with acidic soils surrounding a body of open water. Bogs have a flora dominated by sedges, heaths, and sphagnum.

brackish water

areas with salty water, usually in coastal marshes and estuaries.

cosmopolitan

having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.

crepuscular

active at dawn and dusk

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

detritivore

an animal that mainly eats decomposed plants and/or animals

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

estuarine

an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

freshwater

mainly lives in water that is not salty.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

hibernation

the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.

internal fertilization

fertilization takes place within the female's body

intertidal or littoral

the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.

marsh

marshes are wetland areas often dominated by grasses and reeds.

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

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oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

parthenogenic

development takes place in an unfertilized egg

polar

the regions of the earth that surround the north and south poles, from the north pole to 60 degrees north and from the south pole to 60 degrees south.

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

semelparous

offspring are all produced in a single group (litter, clutch, etc.), after which the parent usually dies. Semelparous organisms often only live through a single season/year (or other periodic change in conditions) but may live for many seasons. In both cases reproduction occurs as a single investment of energy in offspring, with no future chance for investment in reproduction.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

References

Bright, E. 2009. "The Chironomid Home Page" (On-line). Accessed May 11, 2009 at http://insects.ummz.lsa.umich.edu/~ethanbr/chiro/.

Coffman, W., L. Ferrington Jr.. 1996. Chironomidae. Pp. 591-754 in R Merritt, K Cummins, eds. An Introduction to the Aquatic Insects of North America. Dubuque, Iowa, USA: Kendall/Hunt Publishing Company.

Foote, B. 1987. Chironomidae (Chironomoidea). Pp. 762-764 in F Stehr, ed. Immature Insects, Vol. 2. Dubuque, Iowa, USA: Kendall/Hunt Publishing Company.

McCafferty, W. 1983. Aquatic Entomology: The Fishermen's and Ecologists' Illustrated Guide to Insect and Their Relatives. Boston, Massachusetts, USA: Jones and Bartlett Publishers, Inc..