584 DIPTERA. 
with none on the last segment. The head is quite distinctly separate 
from the body, and is horny, with a pair of strong flat jaws. Many of 
Fig. 379— Larva of mycetophila anoyliformans 
(AFTER HOLMGREN) MUCH ENLARGED. 
the larvae secrete a slimy silky substance with which they spin a kind 
of web over their food and subsequently a cocoon within which they 
pupate. Their habits are often very curious and interesting ; for instance, 
the gregariousness of the larvae of some of the Sciarinae, which travel 
about stuck together with slime in large snake-like masses sometimes 
three or four yards long; the extraordinary form of Mycetophila 
ancyliformans which looks exactly like a small Mollusc, the shell being 
represented by a spirally-marked case of excrement which is carried 
on the back (fig. 379), and the strong luminosity recorded as being 
exhibited by a New Zealand Bolitophila ( B. luminosa). The pupae are 
as a rule smooth, without points, spines, or bristles, and not enclosed in the 
larval skin ; they are generally protected by a cocoon, which is, however, 
often very slight and delicate. On emergence the abdomen of the fly, 
more especially of the female, is often noticeably long and large, and 
takes some time to shrink to its normal size, this telescopic extension 
of the posterior abdominal segments being also very obvious during 
oviposition. The whole life-history occupies as a rule about three 
weeks or a month in temperate climates. 
The larvae are essentially scavengers, apart from this being of little 
importance economically, and though in Europe they sometimes attack 
