Morphology of Diptera

They have prominent compound eyes on a mobile head, and (at most) one pair of functional, membraneous wings,[1] which are attached to a complex mesothorax.

The order's fundamental peculiarity is its remarkable specialization in terms of wing shape and the morpho-anatomical adaptation of the thorax – features which lend particular agility to its flying forms.

[1][2] 1: prescutum; 2: anterior spiracle (stigma); 3: scutum; 4: basicosta; 5: calyptra; 6: scutellum; 7: alary nerve (costa); 8: ala; 9: urite; 10: haltere; 11: posterior spiracle (stigma); 12: femora; 13: tibia; 14: spur; 15: tarsus; 16: propleura; 17: prosternum; 18: mesopleura; 19: mesosternum; 20: metapleura; 21: metasternum; 22: compound eye; 23: arista; 24: antenna; 25: maxillary palpi; 26: labrum (inferiore); 27: labellum; 28: pseudotrachae; 29: tip.

In the Nematocera, the dorsal–ventral part of the head extends forward from the eyes due to the development in length of the clypeus and subgenal area (subgena), the distal end of the extension is the 'mouthparts'.

In the "higher" Diptera the head has a subglobose shape and the fronto-clypeus is an area bounded superiorly by the eyes and the vertex.

In Cyclorrhapha Schizophora, a morphological element of particular importance is the presence of the ptilinal suture formed by the resorption of the ptilinum after emergence from the pupa.

The morphology of the compound eye is characterized by a significant number of ommatidia, of the order of thousands in muscoids.

For the purpose of systematics, the presence, the arrangement, and the conformation of the cephalic bristles is important and they have a specific terminology.

(The frontal and vertex plates of the frons can be visualised on the basis of the arrangement of the frontal and orbital bristles); ocellar bristles are located on the vertex between the ocelli; outer and inner vertical bristles are located on the border between the vertex and the occiput and near the upper corner of the eyes; postvertical bristles are located behind the ocelli on the occiput near the median line of the head; vibrissae usually arrayed in small numbers along the facial sections of the arcuate suture, near the margin of the oral cavity; sometimes they ascend along the suture over a greater or lesser distance, occasionally almost to the place of antennal attachment; false vibrissae-bristles are placed along the margin of the oral cavity.

Steyskal (1976) proposed the name "postocellar bristle" the adopted term in the Manual of Nearctic Diptera (McAlpine, J.F., 1981) and the Manual of Palaearctic Diptera (Bernhard Merz, Jean-Paul Haenni, 2000) and, therefore, this term occurs widely in the literature that refers to these two fundamental works.

Two other bristles, present only in some families of Acalyptratae, are located posteriorly and laterally to the ocellar triangle, and are called "internal occipital" in old literature.

The characters taken into consideration are presence or absence, the number, and the position of setae and groups of hairs on the The fundamental peculiarity of the Diptera is the remarkable evolutionary specialization achieved in the shape of the wings and the morpho-anatomical adaptation of the thorax.

The level of specialization – anatomical, functional and morphological – is such that in general these insects fly, often exceptionally, well, with particular reference to agility.

In consequence of this morphological structure, the mesothorax represents the segment of greater development and complexity, while the prothorax and metathorax are considerably reduced.

The most encountered terms used in Diptera identification keys are:– The scutellum is nearly always distinct, but much smaller than (and immediately posterior to) the mesoscutum.

The femora and tibia may bear combinations of dorsal, anterodorsal, posterodorsal, ventral, anteroventral and posteroventral bristles.

This morphological adaptation is often accompanied by sclerotisation of the terminal eighth urite, so that the ovipositor is able to penetrate through the tissues of the organism which will accommodate the eggs and larvae.

In the male, the last urites undergo a complex transformation to form a device, integrated with the genitalia called the hypopygium.

The degree and nature of structural change varies according to the systematic group, but usually involves the development of the lobes of the ninth urotergite into forceps (epandrium) and IX urosterno (hypandrium).

The head is usually devoid of eyes, has chewing mouthparts, modified antennae with up to six segments, more or less developed or reduced to papillae.

The larvae of Brachycera Cyclorrhapha have a wormlike appearance, with little differentiation of body regions (head, thorax, abdomen) to the point that they are commonly called, improperly, worms.

Simplified mouthparts, represented by two jaws shaped like a hook and a series of internal cephalic sclerites, which form in the complex cephalo-pharyngeal apparatus unlike other chewing mouthparts, the hooks of the cephalo-pharyngeal apparatus are equipped with movements along a vertical plane.

Special morphological adaptations are observed in larvae adapted to live in an aquatic environment or as endoparasitoids: for example, sapropagous aquatic larvae of Eristalis which have a long respiratory siphon, which allows them to live immersed in slushy or in putrid waters, while those of Tachinidae have breathing tubes that lead into tracheae of the host or outside of the host's body.

The way in which the opening of the puparium, at the time of adult emergence, distinguishes between two large systematic groups, the Aschiza and Schizophora.

Obtect pupae are generally free and unprotected, with the exception of those of Simuliidae, which are protected by bozzoletti constructed with debris cemented together by silk.