Aquatic Invertebrates of Montana

Diptera

Introduction

Flies, also called true flies or two-winged flies. The second largest order with over 120,000 described species worldwide. About 108 families and over 18,000 species in North America north of Mexico. Most families are terrestrial, but about 28 families and half of all Diptera species have aquatic or semiaquatic larvae. Endopterygota, holometabolous.

Recognition

Larvae without external wingpads and without segmented thoracic legs, but prolegs and crochets are common. The typical insect body segmentation distinguishes fly larvae from both unsegmented worms and segmented worms. Among the insects, only a few Coleoptera and many Hymenoptera, which may parasitize aquatic insects, are likely to be mistaken for Diptera larvae. Larvae may be apneustic, amphipneustic or metapneustic. Adults with one pair of membranous wings, the hind wings heaving been modified into halteres, they have sucking mouth parts. Pupae with one pair of wingpads, that may be free (exarate); fused, but visible (obtect); or concealed within the cuticle (puparium) of the last larval instar (coarctate). The pupa normally has the habitat of the larva.

Life Cycle

Eggs may hatch quickly or undergo long periods of diapause. The first instar of some lentic species is planktonic. Most aquatic Diptera species have 3 or 4 larval instars. Pupation of most of the fully aquatic species occurs underwater, the more semiaquatic species may pupate above water. The pupae may swim to the surface before the adult emerges or it may remain on the bottom. Most species are univoltine or multivoltine, but a some are semivoltine. Adults are terrestrial, mostly short lived, and they may or may not feed before mating. Many have mating swarms. Some species are parthenogenetic. Eggs are laid in or near the water.

Trophic Roles

Larvae assume all trophic roles- scrapers, collectors, shredders, and predators are well represented, some are plant miners and parasitoids. Adults may feed little or not at all, or they may be predators of other insects or molluscs, take pollen and nectar, or feed upon the blood of vertebrates.

Communities

Diptera communities are usually very complex in all types of aquatic systems with many species separated by habitat, habits, season, and trophic role. Chironomids alone usually have over 50 species present at any undisturbed site. Diptera occur in deep lakes, saline and thermal waters and make up the majority of marine insects species. Many species increase in enriched waters with depleted oxygen. Many species are small in size and they have very rapid growth and short life cycles.

Economic Importance

Biting species may be serious pests and they may also serve as vectors of many diseases in man and animals. Many areas must have control programs. Some may damage agricultural plants in wet soils. Some bio-control agents of other pests. Fly larvae often make up the majority of the diet of predacious insects and vertebrates. Non-bitting midges may occur in nuisance numbers. Good environmental indicators when identified to species.

Zoogeography

An ancient group occurring worldwide. Many have relatively low vagility and high evolutionary plasticity. Many adaptive radiations on islands.

Collecting

Many larval dipterans are taken by routine benthic samples. Many species actively burrow through net pores, some strongly avoid nets, many attach very tightly to solid substrates. Many species occur in dense mats of algae and debris and may be extracted by Berlese funnels, if handled gently. Adults can be collected while resting on structures, swept from riparian vegetation, netted from aerial swarms or attracted to lights.

Rearing

Unlike most other holometabolous groups dipterans pupae readily in captivity as long as the larval needs are met.

Preservation

Larvae are best fixed in Kahle's solution and stored in 70% ethanol. Adult specimens might be collected and stored directly into 70% ethanol, but many should be killed in a killing jar and pinned or pointed directly.

Taxonomy

The bitting species are extremely well studied. Most species are based on adults. The larvae are frequently not identifiable to species. Many require carefully prepared slide mounts for identification. Mostly a specialist's group below the family level and especially so at the species level.

Synopsis Of Neartic Families

1. Suborder Nematocera- larvae with horizontally opposable mandibles, head capsule complete and exposed (except retracted in Tipulidae). The adults have the antennal flagellum with 4 or more articulated segments (long-horned flies), and the palps have 3-5 segments. The pupae are obtect to exarate. Mostly aquatic or semiaquatic.
   1. Tipulidae- crane flies, head capsule withdrawn and incomplete posteriorly, burrowers in all types of substrates, many are semiaquatic.
   2. Blephariceridae- net-winged midges, body flattened with 6 divisions and ventral suction disks, scrapers on rocks in rapid current of mountain streams.
   3. Deuterophlebiidae- mountain midges, body with 7 pairs of broad ventrolateral prolegs, antennae forked, on rocks in rapid current.
   4. Nymphomyiidae- body with 8 pairs of slender prolegs, in rapid current among bryophytes in the eastern Canada and adjacent Usa.
   5. Ptychopteridae- phantom (false) crane flies, abdomen terminating in a telescopic siphon, first 3 abdominal segments with ventral prolegs,
   6. Culicidae- mosquitoes, thoracic segments fused and wide, antennae not prehensile, no prolegs.
   7. Chaoboridae- phantom midges, thoracic segments fused and wide, antennae prehensile, no prolegs, limnetic and littoral predators.
   8. Dixidae- dixid midges, paired prolegs with crochets on first 2 abdominal segments, paired post-spiracular lobes above last abdominal segment.
   9. Simulidae- black flies, abdominal segments 5-8 swollen, last abdominal segment with a circle of hooks, prothorax with unpaired proleg, head with labral fans, filter feeders on solid substrates in moderate to rapid current.
   10. Thaumaleidae- solitary midges, amphipneustic, unpaired prothoracic and anal prolegs, scrapers on vertical rock surfaces covered with a film of water.
   11. Chironomidae- midges, also Tendipedidae, prothorax with proleg, body smooth, apneustic.
   12. Ceratopogonidae- biting midges, punkies or no-see-ums, also Heleidae, apneustic, either prothorax with prolegs and all body segments with prominent dorsal tubercles, or without prothoracic prolegs and body segments smooth.
   13. Psychodidae- moth flies, all body segments secondarily divided into 2-3 subdivisions, amphipneustic, sewers to cold mountain streams.
   14. Tanyderidae- primitive crane flies, last 2 abdominal segments with 6 long filamentous processes.

    

2. Suborder Brachycera- larvae head capsule reduced and retracted and mandibles or mouth-hooks are vertical-biting and non- opposable. Adults with antennal flagellum consolidated into a single segment (may be annulated) usually with a style or arista (short-horned flies), palps with 1-2 segments, coarctate pupae. Most families are terrestrial, but some are partially aquatic or semiaquatic.
   1. Division Orthorrhapha (Tabanomorpha + Asilomorpha)- larval head capsule with dorsal portion somewhat developed, the antennae are well developed and located on a sclerotized dorsal plate.
      1. Stratiomyidae- soldier flies, body flattened, integument tough.
      2. Tabanidae- horse flies and deer flies, first 7 abdominal segments with 3-4 pairs of fleshy creeping welts, predators in dense debris.
      3. Athericidae (Rhagionidae in part)- abdominal segments with prolegs bearing crochets and lateral and dorsal slender projections which increase in size posteriorly, lotic predators.
      4. Pelecorhynchidae- larvae are cylindrical with smooth and shiny integument.
      5. Empididae- dance flies, head capsule reduced to slender rods, usually apneustic and usually with abdominal paired prolegs with crochets, but may be like dolichopodids except for the head rods.
      6. Dolichopodidae- long-legged flies, head capsule reduced to rods, but the dorsal pair are expanded posteriorly, posterior spiracles open, abdomen with creeping welts
   2. Division Cyclorrhapha (Muscomorpha)- larval head capsule absent, antennae absent or located on a membranous surface, pharyngeal skeleton fused into a compact characteristic body.
      1. Syrphidae- flower flies, rattail maggots, last abdominal segment with a long telescoping respiratory tube, posterior spiracles very close together, mouth hooks absent, collectors in stagnant lentic waters.
      2. Sciomyzidae- marsh flies, cephalopharyngeal skeleton with a sclerotized toothed arch below the mouth hooks, posterior spiracles separated and only slightly elevated, integument with short fine hairs, some snail predators.
      3. Ephydridae- shore and brine flies, posterior spiracles separated and moderately to strongly elevated, integument of posterior segments covered with setae, lentic collectors, many in saline and thermal waters.
      4. Muscidae- (Anthomyiidae) house flies and relatives, posterior spiracles separated and moderately to strongly elevated, integument without setae.

Montana Species list

Other Sites

• UD Diptera page
• Tree of Life Diptera page
• U.I.A. Freshwater Ecology - The Chironomid home page

Updated on 23 NOV 1995 D.L. Gustafson