This is just a beginning brief sketch.
The true flies possess only one pair of functional wings [the second set of wings has been reduced to small, club-shaped balancing organs called "halteres", see the Crane Flies below for good images of these]. They also have very large eyes, and typically have sucking mouthparts that feed on plants, decaying organic matter, or blood.. The Diptera include flies, mosquitos, gnats, midges, and no-see-ums, and number about 120,000 species worldwide. The oldest known fossils are late Triassic Period in age.
House Flies (Muscidae Family)
House Flies are found worldwide. Most lay their eggs in rotting or at least damp matter, and the larvae can pupate very quickly. Here, below, is a Saguaro-Juniper area House Fly, in Lower Hot Springs Canyon June 01 2004. On the left probing the sweat at the base of a human thumb, the other two on sunny rocks. Click on each image to enlarge it.
Hover Flies (Syrphidae Family)
Hover Flies are also worldwide in distribution. They are distinctive in their behavior: they are also called Flower Flies because they "hover and dart between flowers" (McGavin, cited on main Arthropod page, p. 153). Many of them look very wasp-like in shape, and many have yellow abdomen bands like wasps (though some are more bee-like). Here are views from a pair of many of this species seen feeding on the numerous Desert Chicory flowers on our lands in April 2005: (Click on each image to enlarge it.)
McGavin (ibid.) observes that the large eyes of the males usually meet on top of the head, while those of females are "well separated", suggesting that this one is definitely a male (Click on this image to enlarge it.).
They lay their eggs where their larvae feed. While adults consume pollen and nectar, many species' larvae are predatory upon other arthropods, some even living inside the nest of social hymenoptera, feeding on pupae.
We then saw one atop a Brittlebush flower, and moved to photograph it, but were surprised to see first a golden blob attached to it, then watched the whole beast move, revealing a Brittlebush-colored spider carrying its victim away down a silken line, culminating in the image at right:
This remarkable spider has already sucked the abdomen of the Hover Fly dry. See Brittlebush for more details on this event.
Note also the reddish coloring of part of the fly's legs, not visible in the other photographs.
Crane Flies (Tipulidae Family)
These flies have characteristically very long and fragile legs, which readily break off if the insect is caught (as the male below left shows -- one of its legs is missing). The front of the head is very elongated, and the thorax swollen. The abdomen is long and slender, ending in a blunt tip in males (shown below). The wings are long also. The images below center and right show more details (click on each of these images to enlarge it), the right-hand image showing both the rather short antennae and the distinctive feature of the Diptera,or "Two-wings": "the hindwings [characteristic of other flying insects] are reduced to small, club-shaped balancing organs called halteres." (McGavin, cited on Arthropod page, p. 136) The enlargement at right shows a haltere clearly.
Females contrast with males in having a pointed ovipositor at the end of their abdomen, as shown below (click on each image to enlarge it):
Crane Flies exist in some 15,000 species, and are found worldwide, most often in damp, shaded woodland. (Some larvae are aquatic predators.) To uninformed observers, they may be misidentified as huge mosquitoes (also members of the Diptera Order). These hapless captives/victims above were found flying to light in the grassy mesquite bosque near Teran Wash in early April 2005. Many species of this family are short-lived, and the adults -- who are obviously large and (unlike mosquitoes) fly rather clumsily -- are readily taken by birds. They usually lay their eggs in soil and the larvae eat various kinds of plant material.
Blow Flies (Calliphoridae Family)
Blowflies are found worldwide, and land upon flowers, vegetation, carcasses, and human food. They are "typically stout and may be metallic green or blue, shiny black, or dull" (McGavin, op.cit., p. 143). They are also distinct in having stout bristles on both thorax and abdomen, as you can see on these closer views, images from April 2005 (below): (Click on each image to enlarge it.)
All of these photographs captured a single creature, which had become strongly attracted to the deerskin glove (the portion which had just been stained with a grape-juice-laden drink). This one was a shiny black, and in the enlargements you can see the arrays of bristles quite clearly.
McGavin observes of the Family that "Blow flies lay eggs on carrion, dung, and flesh. The larvae of certain species are predators of ants, termites, and other insect larvae and eggs, and a few suck the blood of nestlings.... Many blow flies lay their eggs on livestock and humans and carry disease.... A few... burrow into human flesh and have been used in surgery as a way of removing dead tissue." (Ibid.)
This small fly below was photographed in late April 2006 in lower Hot Springs Canyon. It was clearly attracted to some fruit juice being drunk by the photographer. (Click on each image to enlarge it.)
Perhaps it is a member of the Family Anthomyiidae, the name meaning literally "flower flies", since the adults feed on nectar and pollen, and are important pollinators. The common name however is "Root-maggot Flies" because most Anthomyiidae larvae feed on roots, (though a few are parasitic on other insects, reptiles, and burrowing mammals). Some of these flies are gray with black markings, including black patches on the abdomen.