Chironomidae (genus)

Chironomidae , commonly known as non-biting midges or chironomids , are a family of Nematoceran flies with a global distribution. They are closely related to the families Ceratopogonidae, Simuliidae, and Thaumaleidae. Although many chironomid species superficially resemble mosquitoes, they can be distinguished by the absence of the wing scales and elongated mouthparts characteristic of the Culicidae (true mosquitoes).

The name Chironomidae stems from the Ancient Greek word ''kheironómos'', "a pantomimist".

Common names and biodiversity

This is a large taxon of insects. Some estimates of the species numbers suggest well over 10,000 world-wide. Males are easily recognized by their plumose antennae. Adults are known by a variety of vague and inconsistent common names, largely by confusion with other insects. For example, chironomids are known as "lake flies" in parts of Canada and Lake Winnebago, Wisconsin, but "bay flies" in the areas near the bay of Green Bay, Wisconsin. They are called "sand flies," "muckleheads," "muffleheads," "Canadian soldiers," or "American soldiers" in various regions of the Great Lakes area. They have been called "blind mosquitoes" or "chizzywinks" in Florida. In Kansas, they are known as "midges." However, they are not mosquitoes of any sort, and the term "sandflies" generally refers to various species of biting flies unrelated to the Chironomidae.

The group includes the wingless ''Belgica antarctica'', the largest terrestrial animal of Antarctica.

Their larvae produce silk, and Chironomus has been studied as an alternative source of silk other than the silk moth, as it is possible to extract it without killing the animal (Ahimsa silk).

The biodiversity of the Chironomidae often goes unnoticed because they are notoriously difficult to identify and ecologists usually record them by species groups. Each morphologically distinct group comprises a number of morphologically identical (sibling) species that can only be identified by rearing adult males or by cytogenetic analysis of the polytene chromosomes. Polytene chromosomes were originally observed in the larval salivary glands of ''Chironomus'' midges by Balbiani in 1881. They form through repeated rounds of DNA replication without cell division, resulting in characteristic light and dark banding patterns which can be used to identify inversions and deletions which allow species identification. Alternatively, DNA barcoding is able to distinguish most species in many taxonomic groups using divergence patterns of commonly-studied gene regions.

Fossil record

The oldest chironomid fossil, ''Aenne triassica'', dates back to the Late Triassic epoch. By the Late Cretaceous, chironomids were highly diverse. Tanytarsins appear in the fossil record during the Middle Eocene.

Behavior and description

Chironomids as a group are very diverse in their life histories, and exhibit a variety of behaviors during their development. Due to their species ambiguity and this diversity of behaviors, there is much controversy in research on their feeding habits, particularly as adults.

Many reference sources in the past century or so have repeated the assertion that the chironomidae do not feed as adults, but an increasing body of evidence contradicts this view. Adults of many species do, in fact, feed. The natural foods reported include fresh fly droppings, nectar, pollen, honeydew, and various sugar-rich materials.

The question whether feeding is of practical importance has by now been clearly settled for some ''Chironomus'' species, at least; specimens that had fed on sucrose flew far longer than starved specimens, and starved females longer than starved males, which suggested they had eclosed with larger reserves of energy than the males. Some authors suggest the females and males of certain species apply the resources obtained in feeding differently. Generally, Males expend the extra energy on flight, while females use their food resources to achieve longer lifespans. The respective strategies should be compatible with maximal probability of successful mating and reproduction in those species that do not mate immediately after eclosion, particularly in species that have more than one egg mass maturing, the less developed masses being oviposited after a delay. Such variables also would be relevant to species that exploit wind for dispersal, laying eggs at intervals. Chironomids that feed on nectar or pollen may well be of importance as pollinators, but current evidence on such points is largely anecdotal. However, the content of protein and other nutrients in pollen, in comparison to nectar, might well contribute to the females' reproductive capacities.

Larvae of some species are bright red in color due to a hemoglobin analog; these are often known as "bloodworms". Their ability to capture oxygen is further increased by making undulating movements.

Adults can be pests when they emerge in large numbers. They may cause difficulty during driving if they collide with the windshield, creating an opaque coating which obscures the driver's vision. They can damage paint, brick, and other surfaces with their droppings. When large numbers of adults die, they can build up into malodorous piles. They can provoke allergic reactions in sensitive individuals. These allergic reactions have been shown to be caused by the haemoglobins that are primarily found in Chironomidae larval stages.

Ecology and distribution

Chironomids are highly versatile species that can tolerate a very wide range of environmental stresses. They are found in high abundances in many of the habitats they live in, and represent important food sources for a variety of organisms. In addition, they are found representing a significant number of symbiotic relationships with other aquatic insects, terrestrial insects, and some plants.

They are distributed, and in most cases found in high abundance globally. They are found in a wide variety of habitats, from the glaciated areas of the tallest mountains, to the deepest bodies of freshwater.

Habitats

Aquatic habitats

Larval stages of the Chironomidae can be found in almost any aquatic or semiaquatic habitat. In fact, in many freshwater aquatic habitats, especially polluted ones, chironomids are often one of the most abundant insects found. Aquatic habitats can be marine or freshwater, the latter including treeholes, bromeliads, interstitial and benthic zones, as well as man-made sewage and artificial containers. They can also be found inhabiting plant held waters, intertidal zones, interstitial zones. Many species of chironomids are found residing in sediments or benthic levels of water bodies, where Dissolved oxygen is very low.

A number of chironomid species inhabit marine habitats. Midges of the genus '' Clunio'' are found in the intertidal zone, where they have adjusted their entire life cycle to the rhythm of the tides. This made the species '' Clunio marinus'' an important model species for research in the field of chronobiology.

Terrestrial habitats

Chironomid larvae can also be found in some terrestrial habitats. Many species that are terrestrial are found living in soil as a dominant part of soil fauna community, particularly in wet soil habitats but also in agricultural land and in early stages of succession. Some species will use humic soils to develop as larvae on land; usually using decaying vegetation or sometimes living vegetation to survive. One genus of chironomids, '' Camptocladius'', are known to develop as larvae in cow dung. There are also some that are known to burrow deep into soil in cases of temporary aquatic habitats or droughts.

Chironomid adults are predominately found in terrestrial habitats.

Roles in the ecosystem

Chironomidae have variable feeding ecology: most species feed on algae and other small soil organisms they can filtrate. Some commensal species feed off of algae on their hosts, which also provides the benefit of protection and additional mobility; particularly when their chosen host site is another predatory larval species. Some species are parasitic, and pierce the integument of its host in order to feed off of its hemolymph.

Larvae and pupae are important food items for fish, such as trout, banded killifish, and sticklebacks, and for many other aquatic organisms as well such as newts. Many aquatic insects, such as various predatory hemipterans in the families Nepidae, Notonectidae, and Corixidae eat Chironomidae in their aquatic phases. Additionally, predatory water beetles in families such as the Dytiscidae and Hydrophilidae have been found to feed on larval chironomids. Flying midges in their adult stage are eaten by fish and insectivorous birds, such as swallows and martins. They are also thought to be an especially important food source for tufted duck chicks during their first few days of life. They also are preyed on by bats and flying predatory insects, such as Odonata and dance flies.

They form an important fraction of the macro zoobenthos

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