Animal Diversity Web

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)

• Biogeographic Regions
• nearctic
  • native
• palearctic
  • native
• oriental
  • native
• ethiopian
  • native
• neotropical
  • native
• australian
  • native
• antarctica
  • native
• oceanic islands
  • native

• Other Geographic Terms
• cosmopolitan

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)

• Habitat Regions
• temperate
• tropical
• polar
• terrestrial
• freshwater

• Terrestrial Biomes
• forest
• rainforest

• Aquatic Biomes
• benthic
• lakes and ponds
• rivers and streams
• temporary pools
• brackish water

• Wetlands
• marsh
• swamp
• bog

• Other Habitat Features
• riparian
• estuarine
• intertidal or littoral

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)

• Other Physical Features
• ectothermic
• heterothermic
• bilateral symmetry

• 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)

• Development - Life Cycle
• metamorphosis

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)

• Key Reproductive Features
• semelparous
• seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• parthenogenic
• sexual
• fertilization
  • internal
• oviparous

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)

• Key Behaviors
• flies
• natatorial
• nocturnal
• crepuscular
• motile
• sedentary
• hibernation
• solitary

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)

• Primary Diet
• detritivore

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.

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..