Calliphoridae

The Calliphoridae (commonly known as blow flies, blow-flies, carrion flies, bluebottles, greenbottles, or cluster flies) are a family of insects in the order Diptera, with 1,200 known species. The maggot larvae, often used as fishing bait, are known as gentles. The family is known to be polyphyletic, but much remains disputed regarding proper treatment of the constituent taxa, some of which are occasionally accorded family status (e.g., Bengaliidae, Helicoboscidae, Polleniidae, and Rhiniidae). The name blow fly comes from an older English term for meat that had eggs laid on it, which was said to be fly blown. The first known association of the term 'blow' with flies appears in the plays of William Shakespeare: Love's Labour's Lost, The Tempest, and Antony and Cleopatra. Calliphoridae adults are commonly shiny with metallic colouring, often with blue, green, or black thoraces and abdomens. Antennae are three-segmented and aristate. The arista are plumose the entire length, and the second antennal segment is distinctly grooved. Members of Calliphoridae have branched Rs 2 veins, frontal sutures are present, and calypters are well developed. The characteristics and arrangement of hairlike bristles are used to tell the difference between members of this family. All blow flies have bristles located on the meron. Having two notopleural bristles and a hindmost posthumeral bristle located lateral to presutural bristle are characteristics to look for when identifying this family. The thorax has the continuous dorsal suture across the middle, along with well-defined posterior calli. The postscutellum is absent or weakly developed. The costa is unbroken and the subcosta is apparent on the insect. Most species of blow flies studied thus far are anautogenous; a female requires a substantial amount of protein to develop mature eggs within her ovaries (about 800 µg per pair of ovaries in Phormia regina). The current theory is that females visit carrion both for protein and egg laying, but this remains to be proven. Blow fly eggs, usually yellowish or white in color, are about 1.5 mm × 0.4 mm, and, when laid, look like rice balls. While the female blow fly typically lays 150–200 eggs per batch, she is usually iteroparous, laying around 2,000 eggs during the course of her life. The sex ratio of blow fly eggs is usually 50:50, but one exception is females from two species of the genus Chrysomya (C. rufifacies and C. albiceps), which are either arrhenogenic (laying only male offspring) or thelygenic (laying only female offspring). Hatching from an egg to the first larval stage takes about eight hours to one day. Larvae have three stages of development (instars); each stage is separated by a molting event. The instars are separable by examining the posterior spiracles, or openings to the breathing system. The larvae use proteolytic enzymes in their excreta (as well as mechanical grinding by mouth hooks) to break down proteins on the livestock or corpse on which they are feeding. Blow flies are poikilothermic – the rate at which they grow and develop is highly dependent on temperature and species. Under room temperature (about 20 °C), the black blow fly Phormia regina can change from egg to pupa in 150–266 hours (six to 11 days). When the third larval stage is complete, it will leave the corpse and burrow into the ground to pupate, emerging as an adult seven to fourteen days later. Adult blow flies are occasional pollinators, being attracted to flowers with strong odors resembling rotting meat, such as the American pawpaw or dead horse arum. Little doubt remains that these flies use nectar as a source of carbohydrates to fuel flight, but just how and when this happens is unknown. One study showed the visual stimulus a blow fly receives from its compound eyes is responsible for causing its legs to extend from its flight position and allow it to land on any surface.