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True Flies

Brian M. Wiegmann and David K. Yeates *

     ================== Tipulidae 
     |  =============== Blephariceromorpha 
     |  |
     |  |============== Axymyiidae 
     |  |
     |  |        ====== Culicimorpha 
<<===|  |        |
     ===|     ===|  === Tanyderidae 
        |=====|  ===|
        |     |     === Ptychopteridae 
        |     |
        |     ========= Psychodomorpha 
        =============== Bibionomorpha 

                   ?=== Brachycera 
Tree from Wood and Borkent (1989)

Containing clade: Endopterygota top

Table of Contents

Characteristics of Diptera
Major Groupings of Diptera
Discussion of Phylogenetic Relationships


The Diptera are commonly known as (true) flies and include many familiar insects such as mosquitoes, black flies, midges, fruit flies, blow flies and house flies. Flies are generally common and can be found all over the world except Antarctica. Many species are particularly important as vectors of disease in man, other animals, and plants. In addition, much of our knowledge of animal genetics and development has been acquired using the vinegar fly Drosophila melanogaster (family Drosophilidae) as an experimental subject (Lawrence, 1992).

The earliest fossil flies are known from the Upper Triassic of the Mesozoic geological period, some 225 million years ago (Evenhuis, 1995). Since that time they have diversified to become one of the largest groups of organisms. There have been about 120,000 species of flies formally described by scientists; thus about 1 in every 10 animals described is a fly. An equal number of species may await description and most of these will be found in environments that remain to be studied intensively, such as tropical forests.

Flies are holometabolous insects, that is their life cycle involes a major change in form from a soft-bodied, wingless larval stage to a hardened, winged adult.

Larval flies have a variety of common names, such as wriggler and maggot. Fly larvae have an enormous variety of feeding habits, and individual species often have very precise requirements. Many consume decaying organic matter, or are predacious, and a large proportion are parasitic on other insects and other organisms. Adult flies are almost always free-living and fly during the day. They typically consume liquid food such as nectar and other plant exudates, or often decomposing organic matter.

Figure 1. Life Stages of the house fly, Musca domestica


Characteristics of Diptera

The major morphological feature which distinguishes flies from other insects is their reduced hind wings, termed halteres. The halteres are small, club-like structures that function as balancing organs during flight. Thus adult flies have only one pair of functional wings, hence their scientific name-- Diptera (di - two, pteron - wing). A few other groups of insects have also convergently attained a similar two-winged form, such as male coccoids (Hemiptera-Sternorrhyncha). A few flies have lost their wings (and halteres) altogether.

Because of the reliance on the forewings for flight, the mesothorax has become enlarged to contain the enormous flight muscles, and the pro- and metathorax are correspondingly reduced.

The mouthparts of flies are also characteristically suctorial and many have large fleshy pads with drainage canals termed pseudotracheae for efficient liquid uptake. Some flies have mouthparts modified for stabbing and piercing other insects, such as the predatory robber-flies (Asilidae) and dance flies (Empididae). Mosquitoes and some other ectoparasitic groups have mouthparts modified for piercing the skin of a vertebrate host and removing blood and other fluids.

Figure 2.A robber fly, family Asilidae, with prey.

Larval Diptera are typically small, pale and soft-bodied. They lack true legs and move by peristaltic waves of muscular contraction through the body. The larvae of most species of flies have a reduced head capsule and all that remains are the mandibles and some associated sclerites which are collectively called the cephalopharyngeal skeleton.

Dipteran pupae have non-functional mandibles (adecticous), and may have the appendages free from the body (exarate), or glued to the body (obtect). If exarate, the pupa is concealed inside the hardened skin (puparium) of the last larval instar.


Major Groupings of Diptera

The Diptera are divided into two suborders, the Nematocera and Brachycera. The Nematocera include generally small, delicate insects with long antennae such as mosquitoes, crane-flies, midges and their relatives. The Brachycera includes more compact, robust flies with short antennae. In older classifications two Divisions were recognised in the Brachycera, the Orthorrhapha and Cyclorrhapha. The "Orthorrhapa" includes brachyceran flies with a simple, obtect pupa, such as horse flies and robber flies, and the Cyclorrhapha comprise brachyceran flies with a pupa enclosed in a hardened puparium. The Cyclorrhapha are further divided into two groups based on the presence or absence of the ptilinum and associated fissure on the head. The ptilinum is a sac which is everted during the emergence of the adult fly to assist in breaking free of the puparium. The Aschiza lack the ptilinum whereas it is present in the Schizophora.

Figure 3. Olbiogaster sackeni, family Anisopodidae, Nematocera. 1996 C. R. Nelson

Figure 4. Milesia scutellata, a flower fly, family Syrphidae, Aschiza, Cyclorrhapha. 1996 C. R. Nelson

Figure 5. Paracantha sp., a fruit fly, family Tephritidae, Schizophora, Cyclorrhapha. 1996 C. R. Nelson


Discussion of Phylogenetic Relationships

The traditional groupings of Diptera have been critically reexamined within a cladistic framework in recent decades by a suite of workers, beginning with the great dipterist Willi Hennig. A consensus has emerged that many of the traditional categories such as the Nematocera, Orthorrhapha and Aschiza are not natural groups (they are paraphyletic). In other words these categories consist of a collection of basal lineages from which the other (monophyletic) catergories (Brachycera, Cyclorrhapha and Schizophora, resepectively) arose. Attempts to formulate a monophyletic classification of Diptera have gained pace recently but no overarching consensus has been reached to date (e.g. Michelsen 1996; Oosterbroek and Courtney 1995; Sinclair et al. 1994; Cumming et al. 1995; Griffiths 1994, 1996). The most comprehensive treatment of dipteran phylogeny and contemporary views on morphological character evidence can be found in Volume 3 of the Manual of Nearctic Diptera (McAlpine and Wood 1989).

The addition of data from broad-based comparative morphological studies of both adult and immature stages (for example, Courtney 1991; Sinclair 1992; Ovchinnikova 1989; Oosterbroek and Courtney 1995) and also from DNA sequences will be critical in the reformulation of dipteran classification. The pages at this web site will document the areas of agreement, outstanding difficulties, and research being conducted to derive a new classification. These are exciting times for students of dipteran classification.



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About this page

The authors wish to thank C.R. Nelsen, N.L. Evenhuis and D. Maddison for comments and suggestions on this page. We also thank C.R. Nelson, M. Stringham, S.J. Scheffer, D. Sear, and J. Baker for providing photographic images.

Brian M. Wiegmann
E-mail: bwiegman@unity.ncsu.edu.
Department of Entomology, Box 7613, North Carolina State University, Raleigh, NC 27695

David K. Yeates
E-mail: d.yeates@mailbox.uq.oz.au.
Department of Entomology, University of Queensland, Brisbane, Qld 4072, Australia

Correspondence regarding this page should be directed to Brian M. Wiegmann, at bwiegman@unity.ncsu.edu.

Page copyright © 1996 Brian M. Wiegmann and David K. Yeates

Last saved 16 January 1997

Title Illustrations

All title figures copyright 1996 C. R. Nelson

Title Figure 1. Tipula (Lunatipula) sp., a crane fly, family Tipulidae.

Title Figure 2. Condylostylussp., a long-legged fly, family Dolichopodidae.

Title Figure 3. Calodexia sp., a parasitoid of army ants from Costa Rica, family Tachinidae.

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