DIPTERA 259 



The mouth-parts of the housefly [Mnsca domestica) have been 

 described on p. 244. The eggs are laid in any rotting organic 

 matter, particularly stable manure, and hatch, in eight to 

 seventy- two hours according to the weather, into maggots or 

 gentles. These are soft, white and legless, and shaped like an 

 ice-cream cone. There are twelve segments, and the head at the 

 pointed end can be withdrawn under the first segment and carries 

 a pair of hook-like mandibles and a pair of minute antennae. 

 The mandibles help to draw the animal forward ; it moves 

 rapidly away from light so that it tends to burrow into organic 

 matter, on which it feeds. Food is liquefied by a sahvary secretion 

 and then sucked in. The second and last segments bear a pair of 

 spiracles each, and the fifth and following somites have each a 

 spiny pad below. The last larval instar buries itself, often away 

 from its food, to a depth of an inch or so, and pupates, the pupa 

 being enclosed in the last larval skin. The imago, which flies 

 towards light, i.e. is positively phototactic, escapes by the 

 inflation of a pecuHar bladder or ptilinum on its head. This is 

 filled with blood under pressure, and used to break successively 

 the pupal skin and puparium, and then to make a way to the 

 open air. The length of life of the larva is from two days to eight 

 weeks, and of the pupa from three days to four weeks or more, 

 according to the temperature, and the imagines may be capable 

 of laying eggs a fortnight after emergence ; a complete generation 

 may therefore be accomplished in three weeks. The first house- 

 flies of the season appear in Great Britain in June and, except 

 for a few which linger indoors, the last are seen on the wing in 

 October or November. Where flies go in the winter time is still 

 unknown. A few may remain as dormant larvae, pupae or imagines, 

 but it is also possible that all die and that those which appear 

 the next summer are immigrants from warmer countries where 

 breeding continues throughout the year. Many imagines are 

 killed at the onset of winter by a fungus, Empitsa mtisccs, which 

 continues to live saprophytically after the fly has died, and may 

 surround its corpse with a grey halo of hyphae. Other related 

 species hibernate as adults. 



The blowflies or bluebottles (Calliphora) lay their eggs on 

 flesh and have a similar Ufe-history to the housefly. Other 

 Diptera are the warble flies and bot flies (Oestridae) with larvae 

 parasitic on hoofed mammals, the hover flies (Syrphidae) which 

 superficially resemble bees, the gadflies or clegs (Tabanidae), 



