Protophormia terraenovae

Protophormia terraenovae is commonly called northern blowfly, blue-bottle fly or blue-assed fly (blue-arsed fly in British English). It is distinguished by its deep blue coloration and large size and is an important species throughout the northern hemisphere. This fly is notable for its economic effect as a myiasis pest of livestock and its antibiotic benefits in maggot therapy. Also of interest is P. terraenovae’s importance in forensic investigations: because of their temperature-dependent development and their prominent presence on corpses, the larvae of this species are useful in minimum post-mortem interval (mPMI) determination. Protophormia terraenovae, of the Calliphoridae family, was named and first described by French entomologist André Jean Baptiste Robineau-Desvoidy in his 1830 “Essai sur les myodaires.” Its genus is shared by one other fly, Protophormia atriceps. Both flies are a dark, undusted, metallic blue-green-black. P. terraenovae is differentiated from P. atriceps by its flat face, plumose arista, and by up to 2 additional pairs of setae along the margin of the scutellum. P. terraenovae’s specific epithet is translated from the Latin as “of the New World.” The oldest-known specimens of P. terraenovae pupae were identified by in 1973 within the fossilized skull of a steppe wisent. The bison skull, estimated to date from the late Eemian period, was excavated from the site of a new sluice for the Brussels-Rupel Canal in Zemst, Belgium. The specimens, although approximately 75,000 years old, are identical in form to the pupae of the modern species. The adult Protophormia terraenovae, one of the larger species of calliphorids, measures between 7 and 12 mm in length. It is characterized by a black to brown anterior thoracic spiracle, a black basicosta, brown wing veins, and dark calypters. Upper calypters sprout black setae. While the thorax and abdomen of P. terraenovae can range in color from dark purple to dark green, the head and legs of this fly are black. Postocular setae are short but prominent; the palpi are yellow or dusky brown. Sexes of the species are easily distinguished by the width of the space between the eyes, the frons: that of the female is .386 times the width of the head, while the frons of the male is only .140 times the head width. Chaetotaxy, the study of setae arrangement, is also useful for determination of sex—for example, the male lacks the fronto-orbital, lateroclinate setae found in the female. These setae are located just at the edge of the frons, near the upper portion of the complex eyes. P. terraenovae larvae are tiny and white, with 12 segments. Length varies by larval age, with the first instar growing up to 2.63 mm and the third, by contrast, as long as 11.87 mm. In the third instar, the last segment is adorned with pointed tubercles, and segment 10 exhibits dorsal spines along its posterior margin. The latter characteristic distinguishes P. terraenovae, 3rd instar, from a similar calliphorid, Phormia regina. Being of the order Diptera, Protophormia terraenovae is holometabolous in its development, meaning it experiences dramatic changes from immature to adult. Protophormia terraenovae undergoes three instars, a pupal stage, and finally an adult stage. First instar larvae obtain a liquid diet from orifices or wounds of a body. The instars that follow digest the body itself. Among the first to colonize, Calliphoridae species are found on the body almost immediately. As eggs hatch into the first larval stage, P. terraenovae begins feeding and increases in size, limited by its chitinous outer cuticle. As P. terraenovae larvae molt into the second instar, feeding intensifies: with larger and more developed mouthparts, second instars are able to break down tougher body tissues.