CHAPTER 14 



Aquatic Diptera 



By Willis W. Wirth and Alan Stone 



Entomology Research Branch 



United States Department of Agriculture 



The Diptera are a large and diverse group of insects 

 which we know commonly under the names of flies, 

 gnats, midges, and mosquitoes. According to Peterson 

 (1951) fully half of the species live in water, utilizing 

 nearly all possible habitats where water may be 

 present. Among the aquatic species are such impor- 

 tant economic pests as mosquitoes, punkies, buffalo 

 gnats, and horse flies, all of which have bloodsucking 

 habits and many of which are vectors of such important 

 diseases as malaria, dengue, filariasis, yellow fever, 

 and encephalitis. On the other hand aquatic Diptera 

 such as midges, crane flies, and brine flies often 

 occur in sufficient quantities to be very important 

 food items of game and food fish and aquatic game 

 birds. 



As denoted by the name Diptera, this order is 

 recognized by the presence of only one pair of wings, 

 the hind pair being reduced to slender, club-shaped 

 balancing organs called halteres. The mouth parts 

 are adapted for sucking liquid food and in many 

 families form a piercing apparatus, at least in the 

 female sex. Other structures are quite subject to 

 modification within the general evolutionary pattern 

 of the order. 



Metamorphosis is complete in the Diptera, the 

 process entailing the usual egg, larval, pupal, and 

 adult stages, although in some families there may 

 occur at times a telescoping of from one to three of 

 these stages (e.g., larviparous Sarcophagidae, Pupi- 

 para, paedogenetic Itonididae). The larvae never 

 possess true legs, although several pairs of prolegs 

 may be present; the body form is extremely diverse, 

 ranging from a simple fusiform type with well-devel- 

 oped head capsule in the primitive groups to the 

 typical, maggotlike larva of the muscoid families. 

 Nearly all types of spiracular arrangement are found 

 in the order, but the aquatic species are most com- 

 monly amphipneustic, metapneustic, or apneustic. 

 The pupae of the primitive families are usually free 

 and active, but in the progressively higher families 

 there is a tendency for the pupa to be enclosed in 

 the last larval skin, which forms a protective, highly 

 sclerotized, barrel-shaped puparium. 



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The variety of habitats occupied by the immature 

 stages of aquatic Diptera is perhaps greater than 

 that of any other order. Aquatic Diptera are known 

 from the intertidal zone of exposed, wave-swept rocks 

 along seacoasts (Tendipedidae; Clunioninae), from 

 thermal waters issuing from springs or geysers at 

 temperatures up to 120° F (Stratiomyidae), from natural 

 seeps of crude petroleum (Ephydridae: Helaeomyia 

 petrolei), and from saturated brine pools (Ephydra 

 cinerea). More normal habitats include the usual 

 standing and running waters where dipterous larvae 

 play their various roles as herbivores, scavengers, 

 and predators. 



We would like to acknowledge again our indebted- 

 ness to O. A. Johannsen of Cornell University whose 

 great work on aquatic Diptera provided the basis for 

 our treatment of this group, and to C. P. Alexander 

 of the University of Massachusetts who supplied the 

 basic information in the first edition for the tipulid 

 section. We have had valuable assistance from pub- 

 lished papers from which we have borrowed freely, 

 manuscript keys which we were permitted to use, and 

 general review and criticism from the following 

 specialists to whom we extend our sincere thanks: 

 Larry W. Quate (Psychodidae), S. B. Freeborn and 

 R. M. Bohart (Culicidae), H. K. Townes (Tendipe- 

 didae), M. T. James (Stratiomyidae), W. W. Middlekauff 

 (Tabanidae) and C. W. Sabrosky (Muscidae, Sarcopha- 

 gidae, and Tetanoceridae). The superb work, Die 

 Larvenformen der DipCeren, which has just been 

 completed by Willi Hennig (1948-1952) has been of 

 extraordinary help in our search of the literature and 

 in our adaptation of generic keys to larvae and pupae. 



It might well be admitted that this study is almost 

 entirely a compilation of keys, descriptions, and 

 figures from many sources, although in great part 

 from the specialists we have named above. For any 

 errors or omissions that we have made in interpreting 

 or copying their work we assume full responsibility. 

 The only families in which our work is in any sense 

 original are the Simuliidae and Tabanidae-Tabaninae 

 (Stone), and Heleidae, Tendipedidae-Clunioninae, 

 Ephydridae, and Canaceidae (Wirth). 



