encyclopedia of inland waters || diptera (non-biting flies)

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Diptera (Non-Biting Flies) G W Courtney, Iowa State University, Ames, IA, USA R W Merritt, Michigan State University, East Lansing, MI, USA ã 2009 Elsevier Inc. All rights reserved. Introduction The Order Diptera consists of a group of familiar insects commonly called true flies or two-winged flies, including mosquitoes, black flies, midges, and house flies. The Diptera are among the most diverse insect orders, with approximately 150 000 described species. These insects are diverse not only in species richness, but also in their structural variety, ecological habits, and economic importance. The group is ubiquitous and cosmopolitan, as they successfully colonized nearly every habitat and all continents, in- cluding Antarctica. Adult dipterans are usually wing- ed and are active fliers. On the basis of feeding, they can be divided into nonfeeding or feeding groups, and the diets of feeding group includes blood, nectar, and other liquefied organic materials. Dipteran larvae are legless and are found in a variety of aquatic habitats. Most larvae are free-living and crawl or swim activ- ely in water (e.g., Chironomidae), sediments (e.g., Tipulidae), saturated wood (e.g., Axymyiidae), or decaying organic material (e.g., Ephydridae). Being a ubiquitous group with diverse habits and habitats, Diptera is economically important. Some groups are of considerable medical and veterinary importance and others can be a general nuisance when present in high numbers or can cause allergic reactions to their hosts through their detached body hairs (e.g., Chironomidae). Despite these negative impacts, flies can play a valuable role as scavengers (e.g., Syrphidae), predators of other insects (e.g., Empididae), pollinators (e.g., Stratiomyiidae), food for vertebrate prey (e.g., Chironomidae), and bioin- dicators of water quality (e.g., Chironomidae). Phylogeny and Classification Traditionally Diptera have been divided into 2–3 sub- orders: Nematocera (‘lower’ Diptera) and Brachycera (‘higher’ Diptera), and the latter sometimes divided further into Orthorrhapha and Cyclorrhapha. Although there is a general agreement that Diptera, Brachycera, Cyclorrhapha, and a few other subordinate groups are natural (i.e., monophyletic) groups, there is com- parably general agreement that the Nematocera is a grade-level (i.e., paraphyletic) grouping. The name itself (‘Nematocera’) conveys that adults of these flies typically possess long, multisegmented antennae. Furthermore, adult nematocerans generally are slen- der, delicate, long-legged flies (e.g., most Tipulidae); however, the group also includes some rather stout- bodied flies (e.g., Axymyiidae and Psychodidae). Larval nematocerans typically have a well-developed, sclerotized head capsule (Figures 1(a)–1(e), 1(g), 1(h), and 2(a)–2(f)), with mandibles that usually rotate at a horizontal or oblique angle. Brachycera adults are characterized by short, 3-segmented antennae. Brachycera larvae usually have a reduced head capsule, consisting mostly slender, sclerotized rods that are partly or largely retracted into the thorax (Figures 1(j)–1(o) and 2(h)–2(l)). Within Brachycera, there are additional differences between orthorrha- phous and cyclorrhaphous groups. The former group (which includes Athericidae, Stratiomyiidae, and a few other families) is similar to nematocerous Diptera in being defined mostly by primitive features. Finally, two major subgroups within the Cyclorrhapha are Aschiza (includes Syrphidae and others) and Schizo- phora (includes the vast majority of families, such as Ephydridae and Sciomyzidae). More details about the relationships and classification of Diptera are provided in some of the references listed in the Further Reading. Morphology Because of the structural variety in dipteran insects, especially among larvae, it is difficult to generalize about their morphology. Despite this variety, flies share many features. Adult flies almost always pos- sess large compound eyes and well-developed anten- nae, with the flagellum being the most varied component. In nematocerous families, the antennae are usually filiform, plumose, or pectinate (Figures 4(a), 5(a), and 5(b)), whereas brachycerous flies typically have antennae that are stylate (Figures 5(c) and 5(d)) or aristate (Figures 4(b), 5(e), and 5(f)). The mouth- parts of adult flies also vary between groups, ranging from vestigial forms (e.g., Deuterophlebiidae) to those that are well developed. The latter include two general types: (1) piercing and sucking, as seen in hemato- phagous (blood-feeding) groups; and (2) lapping and sucking, as seen in Tipulidae and most brachycerous groups. Perhaps the most distinct feature of an adult fly is the single pair of wings (hence, the ordinal name, Diptera, which means ‘two wings’). A related 288

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Page 1: Encyclopedia of Inland Waters || Diptera (Non-Biting Flies)

Diptera (Non-Biting Flies)G W Courtney, Iowa State University, Ames, IA, USAR W Merritt, Michigan State University, East Lansing, MI, USA

ã 2009 Elsevier Inc. All rights reserved.

Introduction

The Order Diptera consists of a group of familiarinsects commonly called true flies or two-wingedflies, including mosquitoes, black flies, midges, andhouse flies. The Diptera are among the most diverseinsect orders, with approximately 150 000 describedspecies. These insects are diverse not only in speciesrichness, but also in their structural variety, ecologicalhabits, and economic importance. The group isubiquitous and cosmopolitan, as they successfullycolonized nearly every habitat and all continents, in-cluding Antarctica. Adult dipterans are usually wing-ed and are active fliers. On the basis of feeding, theycan be divided into nonfeeding or feeding groups, andthe diets of feeding group includes blood, nectar, andother liquefied organic materials. Dipteran larvae arelegless and are found in a variety of aquatic habitats.Most larvae are free-living and crawl or swim activ-ely in water (e.g., Chironomidae), sediments (e.g.,Tipulidae), saturated wood (e.g., Axymyiidae), ordecaying organic material (e.g., Ephydridae).Being a ubiquitous group with diverse habits and

habitats, Diptera is economically important. Somegroups are of considerable medical and veterinaryimportance and others can be a general nuisancewhen present in high numbers or can cause allergicreactions to their hosts through their detached bodyhairs (e.g., Chironomidae). Despite these negativeimpacts, flies can play a valuable role as scavengers(e.g., Syrphidae), predators of other insects (e.g.,Empididae), pollinators (e.g., Stratiomyiidae), foodfor vertebrate prey (e.g., Chironomidae), and bioin-dicators of water quality (e.g., Chironomidae).

Phylogeny and Classification

Traditionally Diptera have been divided into 2–3 sub-orders: Nematocera (‘lower’ Diptera) and Brachycera(‘higher’ Diptera), and the latter sometimes dividedfurther intoOrthorrhapha andCyclorrhapha.Althoughthere is a general agreement that Diptera, Brachycera,Cyclorrhapha, and a few other subordinate groupsare natural (i.e., monophyletic) groups, there is com-parably general agreement that the Nematocera is agrade-level (i.e., paraphyletic) grouping. The nameitself (‘Nematocera’) conveys that adults of theseflies typically possess long, multisegmented antennae.

288

Furthermore, adult nematocerans generally are slen-der, delicate, long-legged flies (e.g., most Tipulidae);however, the group also includes some rather stout-bodied flies (e.g., Axymyiidae and Psychodidae).Larval nematocerans typically have a well-developed,sclerotized head capsule (Figures 1(a)–1(e), 1(g), 1(h),and 2(a)–2(f)), with mandibles that usually rotateat a horizontal or oblique angle. Brachycera adultsare characterized by short, 3-segmented antennae.Brachycera larvae usually have a reduced headcapsule, consisting mostly slender, sclerotized rodsthat are partly or largely retracted into the thorax(Figures 1(j)–1(o) and 2(h)–2(l)). Within Brachycera,there are additional differences between orthorrha-phous and cyclorrhaphous groups. The former group(which includes Athericidae, Stratiomyiidae, and afew other families) is similar to nematocerous Dipterain being defined mostly by primitive features. Finally,two major subgroups within the Cyclorrhapha areAschiza (includes Syrphidae and others) and Schizo-phora (includes the vast majority of families, such asEphydridae and Sciomyzidae). More details aboutthe relationships and classification of Diptera areprovided in some of the references listed in the FurtherReading.

Morphology

Because of the structural variety in dipteran insects,especially among larvae, it is difficult to generalizeabout their morphology. Despite this variety, fliesshare many features. Adult flies almost always pos-sess large compound eyes and well-developed anten-nae, with the flagellum being the most variedcomponent. In nematocerous families, the antennaeare usually filiform, plumose, or pectinate (Figures 4(a),5(a), and 5(b)), whereas brachycerous flies typicallyhave antennae that are stylate (Figures 5(c) and 5(d))or aristate (Figures 4(b), 5(e), and 5(f)). The mouth-parts of adult flies also vary between groups, rangingfrom vestigial forms (e.g., Deuterophlebiidae) to thosethat are well developed. The latter include two generaltypes: (1) piercing and sucking, as seen in hemato-phagous (blood-feeding) groups; and (2) lapping andsucking, as seen in Tipulidae and most brachycerousgroups. Perhaps the most distinct feature of an adultfly is the single pair of wings (hence, the ordinalname, Diptera, which means ‘two wings’). A related

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Antenna

AntennaAntenna

Mandible

Cephalic division

(a)

(c) (d)

(e) (f)

(j)(k)

(n)(o)

(l)

(m)

(g) (h) (i)

(b)

Prothoracic prolegsAnal prolegs

Analpapillae

Antenna

Prolegs

Prolegs

Prolegs

Prolegs

ProlegsProlegs

Mandibular brush

Mandibular hook

Mandibular hook

AntennaAntenna

Basal sclerite

Spiracles

Spiracle

Analpapillae

Analprolegs

Suctorialdiscs

Gills

Figure 1 Larval Diptera. (a): Blephariceridae; (b): Deuterophlebiidae; (c): Chironomidae; (d): Nymphomyiidae; (e): Psychodidae;(f): Tipulidae; (g): Tipulidae head capsule; (h): Chironomidae head capsule; (i): Empididae; (j): Syrphidae; (k): Ephydridae;

(l): Sciomyzidae; (m): Tabanidae cranial sclerites and mouthparts; (n): Dolichopodidae cranial sclerites and mouthparts; (o):

Sciomyzidae cephalopharyngeal skeleton. (Figs a, c, e-o modified from Courtney & Merritt, 2008; Fig b modified from Courtney,1990; Fig d modified from Courtney, 1994.)

Invertebrates _ Diptera (Non-Biting Flies) 289

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(a) (b)

(c) (d)

(e) (f)

(g) (h)

(i) (j)

(k) (l)

Figure 2 Larval Diptera. (a): Axymyiidae; (b): Blephariceridae; (c): Nymphomyiidae; (d): Deuterophlebiidae; (e): Chironomidae;

(f): Psychodidae; (g): Tipulidae; (h): Empididae; (i): Ephydridae; (j): Stratiomyiidae; (k): Sciomyzidae; (l): Syrphidae. (Photographs by

G. Courtney (a-g, i-l) and R. Merritt (h))

290 Invertebrates _ Diptera (Non-Biting Flies)

characteristic is the highly modified thorax, with areduced prothorax and metathorax, and a greatlyenlarged mesothorax. The latter includes severalprominent dorsal and lateral sclerites and, internally,houses much of the wing musculature. Wing venationvaries greatly throughout theDiptera, and can be extre-mely important for identification. The metathoracic

wings are distinctlymodified into club-shaped halteres,which serve as balancing organs.

The dipteran pupa varies considerably in form(Figures 3(a)–3(h)). Some fly pupae look like a crossbetween the worm-like larva and the adult, whereasothers are relatively featureless and seed-like inappearance. The former often have the appendages

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(a)

(c)

(e)

(f)

(g)

(h)

(d)

(b)Wing sheath

Wing sheath

Leg sheath

Respiratory organs

Respiratoryorgans

Respiratory siphon

Respiratory siphon

Respiratory organs

Respiratory organs

Antennal sheath

Antennal sheath

Antennal sheath

Adhesive discs

Adhesivediscs

Wing sheath

Wing sheath

Leg sheath

Leg sheath

Wing sheath

Leg sheath

Figure 3 Pupal Diptera. (a): Nymphomyiidae; (b): Tipulidae; (c): Chironomidae habitus and anal division; (d): Blephariceridae,dorsal (left) and ventral (right) view; (e): Deuterophlebiidae, dorsal (left) and ventral (right) view; (f): Empididae, ventral (above) and

dorsal (below) view; (g): Syrphidae; (h): Ephydridae. (Fig a modified from Courtney 1994; Figs, b-d, f-h modified from Merritt & Webb,

2008; Fig e modified from Courtney, 1990.)

Invertebrates _ Diptera (Non-Biting Flies) 291

fused to the body and are typical of nematocerous flies(Figures 3(a)–3(e)). For instance, a pupal Tipulidaehas an identifiable head, thoracic, and abdominalsegments, but the antennal sheaths, legs, and wingpads adhere to the pupal body (Figure 3(b)). Theexterior of the nematoceran pupa may be adornedwith spines, gill-like respiratory devices, or locomo-tory paddles (Figures 3(b)–3(e)). In contrast, the Bra-chycera form a pupal stage that is more concealed,compacted, or contracted (Figures 3(f)–3(h)). Themost derived of these taxa, the Cyclorrhapha (e.g.,Syrphidae, Ephydridae) form a ‘puparium,’ whichis composed of the hardened skin of the last larval

instar (Figures 3(g) and 3(h)). This relatively tough,desiccation-resistant structure houses and protectsthe pupa. The enclosed adult must break throughthe puparial skin, and does so by extruding a balloon-like structure on the head. Very few external fea-tures are noticeable on the puparium, although carefulexamination will reveal the spiracles through whichatmospheric air is obtained by the pupa.

Dipteran larvae can be distinguished from the larvaeof most other insects by the lack of jointed thoraciclegs. In other features, fly larvae show tremendousstructural variety. This variation is exemplified by cra-nial structure. Larvae of most nematocerous flies are

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(a) (b)

Figure 4 Adult Diptera. (a): Tipulidae; (b): Syrphidae. (Photographs by G. Courtney (a) and M.E. Rice (b))

292 Invertebrates _ Diptera (Non-Biting Flies)

characterized by a complete, fully exposed, andheavily sclerotized head capsule (Figures 1(a)–1(e),1(g), 1(h), and2(a)–2(f)). Crane fly Larvae are a specialcase among nematocerous flies, as the head capsule isoften fully retracted into the thorax and the posteriorcranial margin may possess small to extensive longitu-dinal incisions (Figures 1(f), 1(g), and 2(g)). In contrastto the condition in nematoceran larvae, the head cap-sule of brachyceran larvae are greatly reduced orabsent. The head capsule of many ‘lower’ Brachycera(e.g., Empididae) consists of slender arms and rodsthat are partly retracted into the thorax (Figures 1(i),1(m), 1(n), and 2(h)). The culmination of cranialreduction is exemplified by the head of larval Cyclor-rhapha (e.g., Ephydridae), in which the external por-tions of the head are membranous and much of thehead is retracted into the thorax (Figures 1(j), 1(k),1(l), 1(o), and 2(i), 2(k), 2(l)). In these groups, theinternal portion, or cephalopharyngeal skeleton, com-prises the remnants of internal cranial sclerites (tentor-ium) and various mouthparts. Cranial modificationsare often accompanied by general changes in the shapeand rotation of mandibles and other mouthparts. Themandible of larval nematocerans typically consists of astout, toothed structure that moves in a horizontal oroblique plane and operates as a biting and chewingorgan, whereas the brachyceran larval mandible usu-ally is more claw-like, has fewer teeth along the innersurface, moves in a vertical plane, and operates as apiercing or slashing organ.In most dipteran larvae, the thorax and abdomen

are soft, flexible and only occasionally bear sclero-tized plates. The thorax usually consists of threedistinct segments and the abdomen usually 8 or 9segments. Body form varies almost as much as doescranial diversity and ecological habits. In many nema-toceran groups, the body is subcylindrical. Othergroups are predominantly elongated and serpentine,the latter body form being especially common ingroups inhabiting interstitial aquatic habitats. Thetypical body shape of a cyclorrhaphan larva is that

of a maggot; i.e., pointed at the anterior end, with thethoracic segments approaching the maximum bodydiameter (Figures 1(i), 1(k), and 1(l)).

Despite the absence of jointed thoracic legs, loco-motion is highly diverse in fly larvae, reflecting thegroup’s diversity in habitat and habits. Locomotoryappendages operate through a combination of turgorpressure and muscle action, and include creepingwelts, prolegs, and other specialized structures (e.g.,suctorial discs). Creeping welts are transverse,swollen areas (ridges) that bear one to several modi-fied setae or spines; creeping welts are characteristicof several groups, including many Tipulidae. Amongorthorrhaphous groups, ventral creeping welts arecommon in the larvae of Empididae and Sciomyzidae.Cyclorrhaphan larvae typically use creeping welts asanchoring devices, with welts usually composed ofbands of small spines on abdominal segments. Prolegsusually are paired, round, elongate, fleshy, retractileprocesses that bear apical spines or crochets; prolegscome in a diversity of shapes, sizes, and positions,and are typical of larvae of Chironomidae, Deuter-ophlebiidae, and various members of other groups(Figures 1(b)–1(d), 1(f), 1(i)–1(k), and 2(b)–2(e)).Other specialized structures used for locomotionor attachment include friction pads and suctorialdiscs. Several genera of moth flies (Psychodidae)possess friction pads, which are areas of modifiedcuticle on the ventral surface of the thorax or abdo-men. Functionally similar structures may occur incertain Ephydridae, particularly in groups inhabitingwaterfalls and thin films of flowing water. Suctorialdiscs are true suction devices on the ventral bodysurface of larval Blephariceridae (Figures 1(a) and2(b)) and are an obvious adaptation to life in torren-tial streams.

Larval Diptera show a variety of respiratory adap-tations, many a reflection of life in fluid or semifluidhabitats. The basic respiratory system comprisesof an internal system of tracheae and the externalspiracles. Respiration may be directly from the

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FlagellomeresFlagellomeres

Stylus

Stylus

Arista

Arista

(a) (b)

(c) (d)

(e) (f)

Figure 5 Adult Diptera heads. (a): Tipulidae; (b): Blephariceridae; (c): Asilidae; (d): Empididae; (e): Tachinidae; (f): Syrphidae.

(Photographs by G. Courtney)

Invertebrates _ Diptera (Non-Biting Flies) 293

atmosphere, from plant tissues, or from oxygenatedfluids. The presence of haemoglobin in the blood ofsome Chironomidae can assist the absorption of oxy-gen. Many aquatic larvae, particularly those fromwell-oxygenated streams, lack spiracles and absorboxygen directly through the skin. Some families(e.g., Psychodidae) possess spiracles on the prothoraxand last abdominal segment, while others (e.g., mostcyclorrhaphans) have spiracles on only the lastsegment. In several groups (e.g., many Ephydridae

and Syrphidae), the spiracles are at the end of aretractile respiratory siphon (Figures 1(j), 1(k), and2(k), 2(l)).

Biology and Ecology

Life History

As a holometabolous insect, or one that undergoescomplete metamorphosis, the dipteran life cycle

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294 Invertebrates _ Diptera (Non-Biting Flies)

includes a series of distinct stages or instars. A typicallife cycle consists of a brief egg stage (usually a fewdays or weeks, but sometimes much longer), 3–4larval instars (typically 3 in Brachycera and 4 innematocerous flies), a pupal stage of varying length,and an adult stage that lasts from less than 2 h (Deu-terophlebiidae) to several weeks or even months. Theeggs of aquatic flies are usually laid singly, in smallclusters, or in loose or compact masses in or near thewater and are attached to rocks or vegetation. InDeuterophlebiidae and certain members of someother groups, the female crawls beneath the water toselect oviposition sites, a behavior that ensures eggsare placed in a suitable larval habitat. In most taxa,all larval instars occur in the same habitat and theduration of the first larval stage is shortest, whereasthat of the last instar is much greater, often severalweeks or even months.

Habitat

The diversity of dipteran habitats is partly a reflectionof the different ecological roles of larvae and adults,with larvae generally adapted for feeding and growth,and adults for reproduction and dispersal. Althoughfly larvae occur in both terrestrial and in aquatichabitats, virtually all adults are terrestrial and capa-ble of flight. Wingless and, therefore, flightless groupsinclude certain crane flies and marine midges, aswell as a few representatives of other groups. Adultflies are arguably one of the most aerial of organ-isms. Swarms of flies, which usually consist primarilyof males, are a common sight in many areas. Theseaggregations, often for enhancing male visibility toprospective female mates, may occur along roadsides,over certain trees or bushes, above sunlit pools alongstreams, at the summits of hills, in sunny gaps of forestcanopies, or at any number of other swarm markers.Swarming is probably a primitive feature of Diptera,whichmight explain the prevalence of this behavior innematocerous groups. These Diptera and other fliesshare a number of structural features that might beadapted for swarming, including enlarged compoundeyes and wings with well-developed anal lobes. Thesefeatures and others are thought to assist flies in bothmaneuvering in flight and perceiving conspecific indi-viduals in swarms. Swarming and related behaviorsare especially developed in dance flies (Empididae), agroup known for their predaceous habits and theelaborate behaviors and ‘nuptial gifts’ for prospectivefemale mates. Other groups (e.g., Syrphidae and Stra-tiomyiidae) are among the most agile flying insects,being particularly adept at hovering.Diptera larvae have colonized a wide variety of

terrestrial and aquatic habitats, including water

(e.g., Chironomidae), soil and damp sediments (e.g.,Tipulidae), rotting wood (e.g., Axymyiidae), decay-ing organic material (e.g., Syrphidae), and the tissuesof living organisms (e.g., Sciomyzidae). Despite thediversity of habitats, most larvae are in a broad senseaquatic. Even ‘terrestrial’ groups from decomposingvegetation, carcasses, leaf litter, rotting wood, or soiloften live in a rather aqueous environment. Thisrequirement for a damp environment reflects partlyin that the larval cuticle is usually quite thin, soft, andsusceptible to desiccation. Truly aquatic larvae occurin coastal marine, saline and estuarine waters, shal-low and deep lakes, ponds, cold and hot springs,phytotelmata, artificial containers, slow to torrentialstreams, groundwater zones, and even natural seepsof crude petroleum. Aquatic habits are most preva-lent in larvae of nematocerous flies, including all ormost net-winged midges and common midges.Among brachycerous flies, shore flies and snail-killing flies are most commonly found in aquatichabitats. In some groups, such as crane flies and beeflies, many species have semi-terrestrial larvae.

Trophic Relationships

The trophic diversity and numerical abundance ofDipteran insects make them an important componentin many ecosystems, both as primary consumers andas a food resource for other organisms. Trophic diver-sity is reflected in the wide range of larval feedinghabits, which encompass nearly every functionalfeeding group. In some groups (e.g., most Empidi-dae), larvae and adults belong to the same trophiccategory; in other groups (e.g., Blephariceridae)these life stages adopt different feeding strategies;in others, feeding can be restricted to the larvae(e.g., Deuterophlebiidae). Adding to the variety offeeding habits is that some groups may feed on multi-ple food resources during the same life stage (e.g.,larvae that can be both saprophagous and preda-ceous, and adults that are both nectarivorous andhematophagous). For example, larval Sciomyzidaemay feed on dead or living molluscs, and some Ephy-dridae larvae may consume algal, bacterial, or detritalresources during the same instar.

Saprophagous habits are most prevalent in Diptera,especially in brachycerous groups. Many fly larvaefeed on decaying organic material or organic detritus,where the resident bacteria and other microorganismsare the primary source of nutrition. Decomposingplant fragments can be an important food resourcein aquatic habitats, where the larvae of many Tipuli-dae, Ephydridae, and other groups consume it. Thesegroups and others (e.g., Psychodidae, Syrphidae, Stra-tiomyiidae) also contain many species that feed

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on decaying, fine organic matter and associatedmicroorganisms. In many saprophagous groups, aseive-like pharyngeal filter is used to concentratemicroorganisms and other organic particles.Phytophagous groups, which consume live plants

(including algae and fungi), are well represented bythe larvae of Tipulidae and Chironomidae. Aquatichabitats contain many fly larvae that consume thethin films of algae and organic matter occurring onrocks and other substrata. Among the most obviousof these aquatic grazers are larval Blephariceridae,Deuterophlebiidae, and certain species of Psychodi-dae and Ephydridae.Most predaceous Diptera attack other inverte-

brates as their primary food. Many families (e.g.,Chironomidae, Tipulidae, and Ephydridae) containa few predaceous species, whereas other groups(e.g., nearly all lower Brachycera) feed primarily orexclusively on invertebrates. In many of the latter,vertebrate prey (frogs and salamanders) can be partof the diet. Predaceous larvae typically kill multiplehosts, whereas parasitic and parasitoid larvae gener-ally attack only one host. Of these, the Sciomyzidaeare among the best known aquatic group.

Biology of Selected Families

Selected characteristics of families of aquatic andsemiaquatic Diptera are given in Figure 1. The biol-ogy of selected families is presented below.

Suborder ‘Nematocera’ Axymyiidae (Figure 2(a)).This is a rarely collected and poorly studied group offlies known from widely scattered locations in NorthAmerica and Eurasia. The family contains only fivedescribed species, but additional species are likely.Their biology is largely unknown. In at least somespecies, larvae inhabit saturated, partly submergedwood in headwater streams and seepages. The larvae,which are barrel-shaped but possess a long respira-tory siphon and pinnately branched anal papillae,are highly specialized gougers. As such, these insectsmay play an important role in recycling woodydebris. Larvae inhabit chambers that extend perpen-dicular to the wood surface, where they live forapproximately 2 years before pupating briefly andemerging as adults. Adults are poor fliers, have vesti-gial mouthparts, and apparently do not feed. Almostnothing is known about adult behavior, mating, andoviposition.Blephariceridae (Figures 1(a), 2(b), 3(d), and 5(b)).

Net-winged midges are one of the most distinctiveDiptera families. This group contains more than 300described species, with representatives on most majorcontinents. The immature stages are highly adapted

to life in the cascades, rapids, and waterfalls oftorrential streams. Structural adaptations of larvaeinclude six ventral suctorial discs, which function ashydraulic suckers and allow secure attachment tocurrent-exposed substrata. Larvae persist mainly ona diet of periphytic algae and form a significant pro-portion of the primary consumers in torrenticoloushabitats. Pupae are equally adapted to torrentialstreams, being dorsoventrally compressed, stream-lined, and attached immovably to rocks. Adults areslender-bodied, long-legged, and show a diversity ofhabits. The females of many species are predators ofother insects, including other blepharicerids; femalesof other species and males of most species are nectar-ivorous or nonfeeding. In most species, adults areshort-lived and remain near their natal stream.

Chironomidae (Figures 1(c), 1(h), 2(e), and 3(c)).Common midges comprise the largest family of pri-marily aquatic flies. Although including slightly over5000 described species, the family contains an esti-mated 10 000–15 000 species. They are arguably themost widespread aquatic dipteran, with representa-tives on all continents, including Antarctica, andmany oceanic islands. Chironomids occur in nearlyevery aquatic habitat, ranging from glacial streams at5600m altitude, to lake sediments at a depth of1000m, to marine lagoons. Larvae are vermiform(worm-like) but possess paired prolegs on both theprothorax and the last abdominal division. Theimmature stages of most species are aquatic, butsome species inhabit terrestrial situations such asleaf litter and damp soil. The group includes a diver-sity of larval feeding types, ranging from detritivoresto predators and herbivores. Chironomids are one ofthe most important components of aquatic ecosys-tems, serving as a primary food resource for countlessorganisms. In most groups, adults do not feed; how-ever, some species consume nectar or honeydew.

Deuterophlebiidae (Figures 1(b), 2(d), and 3(e)).Mountain midges are among the most unusualaquatic flies. The family contains a single genus and16 described species, all restricted to western NorthAmerica and central and eastern Asia. These flies areamong the most specialized dipterous insects. Thelarvae and pupae of these small flies (<4mm) areaquatic, found mostly in cold torrential streams,but ranging from small high-gradient creeks to largelow-gradient rivers. Larvae and pupae are restrictedto riffle habitats where they adhere to stones. Theirstructural and ecological adaptations include eversi-ble larval prolegs and flattened, streamlined pupae.Adults have comparatively large wings and malesextremely long antennae. Males also lack tarsalclaws and are incapable of walking (i.e., they mustremain in flight throughout their life). Adults of both

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sexes have vestigial mouthparts, emerge early in themorning, and typically live for less than 2 h. Ovipo-siting females will crawl beneath the water, sheddingtheir wings in the process, and place eggs in the larvalhabitat.Nymphomyiidae (Figures 1(d), 2(c), and 3(a)).

These minute (<2mm length) flies are odd in struc-ture and habits. The family contains a single genusand only seven extant species, with all known speciesrestricted to eastern, central, and southeast Asia andeastern North America. The larvae are compressedlaterally and possess paired, eversible, crochet-tippedventral prolegs on abdominal segments I–VII and IX.Adults have a larviform appearance, lack mouth-parts, and possess compound eyes that are contiguousventrally, wings that are deciduous, elongate, andfringed with long macrotrichia. Most species areassociated with small, headwater streams, where lar-vae, pupae, and copulating adults may occur on rockscovered with aquatic moss. Adults apparently do notfeed and their life span is very short. The group isnoteworthy in their reproductive habits. Copulatingadults will descend into the water, shed their wings,and select an oviposition site. The female then placesa rosette around the coupled adults, which die incopula.Psychodidae (Figures 1(e) and 2(f)). Sand flies,

drain flies, and moth flies are typical representativesof this family. Although the first of these are hema-tophagous and include species capable of diseasetransmission, most psychodids do not bite and areharmless to humans and livestock. Drain flies andmoth flies resemble tiny moths (about 2–4mm long)with hairy, pointed wings. The former can be abun-dant in households and restrooms, where larvaedevelop on the rich organic material that builds upin domestic pipes and drains. Moth flies have aquaticto semiaquatic larvae that breathe atmospheric oxy-gen by maintaining contact with the atmosphereusing hydrofuge hairs on their spiracles. Eutrophiclakes, marshes, and wastewater treatment plantsmay produce large numbers of adults. As detritivores,the larvae of moth flies probably play the role of asignificant nutrient recycler in lentic ecosystems.Tipulidae (Figures 1(f), 1(g), 2(g), 3(b), 4(a), and

5(a)). Crane flies are a diverse, cosmopolitan groupthat inhabits a wide range of freshwater and terres-trial habitats. The moist transition zone betweenaquatic and terrestrial areas supports a large assem-blage of species. Other groups are specialized toinhabit saturated wood and decaying organic mate-rial, and a few species can tolerate high salinity andinhabit the rocky intertidal zones of marine habitats.Larvae of many species are maggot-like, recognizedby a head capsule that is partly retracted into the

thorax. Adults usually are slender with elongate, nar-row wings and delicate legs. Larval feeding habitsinclude nearly every functional feeding group, withshredders, collector-gatherers, and predators beingespecially well represented. Adults generally do notfeed, although the public frequently mistakes themfor giant mosquitoes.

Suborder Brachycera Empididae (Figures 1(i), 1(n),2(h), 3(f), and 5(d)). Dance flies are an important butpoorly known group of brachycerous flies. The 3500described species presumably represents a small frac-tion of the group’s actual diversity. Our lack ofknowledge reflects partly the paucity of informationabout their immature stages, which occur in a varietyof terrestrial, semiaquatic and aquatic habitats.Unfortunately, the larvae and pupae of most specieseither remain undiscovered or have not been defini-tively associated with adult stages. Known larvae aremostly predaceous on other insects. Adults of bothsexes consume insects and nectar; insects may becaptured live, or scavenged from spider webs, thewater surface, or from other habitats. The feedingand mating behavior of empidids may be highlyspecialized, with courtship often involving the trans-fer of food (or a bubble!) from the male to female.Males often are collected in large swarms (hence, thecommon name!).

Ephydridae (Figures 1(k), 2(i), and 3(h)). Theseflies are also known as shore flies, and most taxa areassociated with aquatic habitats. This is one of themost species rich families of Diptera, and one ofthe most diverse in feeding habits. Larvae are consu-mers of decaying organicmatter, secondary stemborersof damaged plants, primary herbivores, generalistand specialist feeders of algae, and predators. Virtuallyall aquatic habitats, from flowing water to stagnantenvironments, temporary to permanent, freshwater tohypersaline, and from cold water to hot springs, areoccupied by ephydrids. Shore flies can be abundant inhuman-made habitats, including constructed wetlandsand sewage treatment plants. It is the only aquaticinsect to inhabit the Great Salt Lake in Utah wheresalinity levels are far greater than sea water!

Stratiomyiidae (Figure 2(j)). Soldier flies are a com-mon and widespread group containing more than2000 species. They are easily recognized in all lifestages. Larvae are unusual in that their body is cov-ered with calcium carbonate ‘warts.’ Adults oftenmimic Hymenoptera, and can resemble bees andwasps. The larvae of most species are aquatic, andmany species can tolerate highly saline water orextreme temperatures (e.g., hot springs); aquatic spe-cies rely on atmospheric oxygen for respiration. Most

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larvae are predators or collector-gatherers. Adultsfeed on pollen and nectar.Syrphidae (Figures 1(j), 2(l), 3(g), 4(b), and 5(f)).

Flower flies are another common and brightly col-ored group that often mimics bees, bumble bees, hor-nets, and other Hymenoptera. Syrphids have theability to hover (thus, they are also known as hoverflies), and individuals are frequently found flying nearflower heads where they obtain nectar. Adults arecommon near wetlands and lakes but are also abun-dant in terrestrial areas where appropriate floweringvegetation grows. In aquatic habitats, larvae arecollector-gatherers, and may use retractable siphonsfor respiration (e.g., Eristalis). Overall, larval habi-tats are diverse, including dung, rotting cactus, peat,and hymenopteran nests.Sciomyzidae (Figure 1(l), 1(o), and 2(k)). These

flies have been given the common names marsh flyand snail-killing fly. Neither name encompasses allthe habits of this well-studied family. Some speciesare found in marshes, but others are fully terrestrial.Many species are larval parasitoids or predators ofsnails, and some attack slugs or fingernail clams; thelarvae of one genus prey on the eggs of aquatic andsemiaquatic snails. The adults range in color fromyellowish brown to brownish black, have antennaethat may be long or short, and vary in size from a fewmillimeters to nearly 1 cm. However, certain morpho-logical characteristics, and the trophic niche ofexploiting freshwater or terrestrial Mollusca, ties allSciomyzidae together evolutionarily.

Economic Importance

Diptera contain several families that can be consid-ered beneficial to humans and their environment.First, and most important, is the role of all Dipterain food chains in nature. For example, larval Chiro-nomidae occur in large numbers and provide a majorprey base for many other invertebrates as well as forvertebrates such as fish, birds, bats, and amphibians.In turn, several families contain predators and para-sitoids as larvae and adults, including the Empididaeand Syrphidae. Many families are important decom-posers and recyclers of decaying organic matter ofdifferent types (e.g., Psychodidae, Stratiomyiidae,and Syrphidae). Some Diptera are important pollina-tors of flowers (e.g., many Syrphidae).Some families of aquatic Diptera have been impor-

tant in water quality and bioassessment studies toclassify the degree of pollution in a water body. Lar-vae of certain midges (Chironomidae: Chironomus)are known as bloodworms because of the hemoglobinin their blood. These and the rat-tailed maggots(Syrphidae: Eristalis) are often used as indicators of

polluted water or water low in oxygen. The larvae ofsome groups, includingmost Blephariceridae as well asother Chironomidae, are associated with clean waterhabitats. Finally, someDiptera have been the subject ofstudy for scientists throughout the world. For example,certain Chironomidae are used in acute and chroniclaboratory toxicity studies to compare toxicants andthe factors affecting toxicity, and to ultimately predictthe environmental effects of the toxicant.

Glossary

Detritus – Organic matter of unidentifiable origin,mainly consisting of partially decomposing plantparts, bacteria, algae, etc.

Hematophagous – Blood feeding, generally referringto biting flies like mosquitoes and black flies.

Monophyletic – A category based on the commonpossession of shared, derived characters; used of agroup derived from a single common ancestor andincluding all descendants of that ancestor.

Nectarivorus – Feeding on nectar of plants.

Paraphyletic – A category based on the common pos-session of shared, primitive characters; used of agroup derived from the a single common ancestorbut not containing all descendants of that ancestor.

Phytotelmata – Plant-held aquatic habitats, such asthose found in pitcher plants, tank bromeliads, andtree holes.

See also: Aquatic Insects, Classification; Aquatic Insects –Ecology, Feeding, and Life History; Benthic InvertebrateFauna, Lakes and Reservoirs; Benthic InvertebrateFauna, River and Floodplain Ecosystems; Benthic Inver-tebrate Fauna, Small Streams; Benthic InvertebrateFauna, Tropical Stream Ecosystems; Benthic Inverte-brate Fauna, Wetland Ecosystems; Diptera (Biting Flies);Vector-Borne Diseases of Freshwater Habitats.

Further Reading

Brown BV (2001) Flies, gnats, and mosquitoes. In: Levin SA (ed.)

Encyclopedia of Biodiversity, pp. 815–826. London: Academic

Press.

Courtney GW (1990) Revision of Nearctic mountain midges(Diptera: Deuterophlebiidae). Journal of Natural History 24:

81–118.

Courtney GW (1994) Biosystematics of the Nymphomyiidae(Insecta: Diptera): Life history, morphology and phylogenetic

relationships. Smithsonian Contributions to Zoology 550: 1–41.Courtney GW and Merritt RW (2008) Aquatic Diptera: Part One:

Larvae of aquatic Diptera. In: Merritt RW, Cummins KW, andBerg MB (eds.) An Introduction to the Aquatic Insects of North

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America, Fourth edn., pp. 687–722. Dubuque, Iowa: Kendall/

Hunt Publishing Co.Merritt RW, Courtney GW, and Keiper JB (2003) Diptera. In:

Resh VH and Carde RT (eds.) Encyclopedia of Insects,pp. 324–340. London: Academic Press.

Merritt RW, Cummins KW, and Berz MB (eds.) (2008) An Intro-duction to the Aquatic Insects of North America, Fourth edn.,

Dubuque, Iowa: Kendall/Hunt Publishing Co.

Merritt RW and Webb DW (2008) Aquatic Diptera: Part

Two: Pupae and adults of aquatic Diptera. In: Merritt RW,Cummins KW, and Berg MB (eds.) An Introduction to theAquatic Insects of North America, Fourth edn., pp. 723–771.Dubuque, Iowa: Kendall/Hunt Publishing Co.

McAlpine JF, Peterson BV, Shewell GE, Teskey HJ, Vockeroth JR,and Wood DM (coordinators) (1981) Manual of NearcticDiptera, Vol. 1. Research Branch, Agricultural Canada Mono-

graph 27.

McAlpine JF, Peterson BV, Shewell GE, Teskey HJ, Vockeroth JR,

and Wood DM (coordinators) (1987) Manual of NearcticDiptera, vol. 2. Research Branch, Agricultural Canada Mono-

graph 28.

McAlpine JF and Wood DM (coordinators). Manual of NearcticDiptera, vol. 3. Research Branch, Agricultural Canada Mono-graph 32.

Oosterbroek P and Courtney GW (1995) Phylogeny of the nema-

tocerous families of Diptera (Insecta). Zoological Journal of theLinnean Society 115: 267–311.

Papp L and Darvas B (eds.) (2000) Manual of Palaearctic Dipteravol. 1. Budapest: Science Herald.

Yeates DK andWiegmann BM (1999) Congruence and controversy:

Toward a higher-level phylogeny of Diptera. Annual Review ofEntomology 44: 397–428.

Yeates DK and Wiegmann BM (eds.) (2005) The EvolutionaryBiology of Flies. New York: Columbia University Press.