616 
DIPTERA. 
Acalyptrate manner in roots of plants and similar places, we have 
here included the Anthomyiids among the Acalyptrates, for the 
convenience of the student. Probably the family is really best placed 
by itself, in a distinct division intermediate between Acalyptrates and 
Calyptrates. 
As a general rule the flies in the first big group (the Acalyptrates) 
are small, often very small. The extremely common little flies which 
are so often seen hovering about a plate of bananas or other fruit are 
typical Acalyptrates (Drosophilidce). The adult Acalyptrate flies are 
usually harmless, and a large number of the larvae are beneficial, feed¬ 
ing on decaying vegetables or in dung, and thus acting as scavengers. 
On the other hand, many of the larvae live in the stems or fruits of plants, 
or are leaf-miners, and sometimes do much damage. 
The flies in the second big group (the Calyptrates) are often 
medium-sized or rather large flies, most of them with a strong family 
likeness to the common House-fly or the Blue-bottle, both" of which 
are typical Calyptrates. A large number of the larvae are scavengers, 
especially the Muscidce and Sarcophagidce, and the maggots of both 
these families sometimes breed in living flesh, as in cases of Myiasis : 
the commonest mode of life among the Calyptrates, however, is that 
of parasitism, and this is practically universal among the Tachi- 
nidce and Oestridce. The pecuniary loss caused every year by the 
attacks on cattle of the larvae of the “Warble-flies ” (Oestridce) must 
be very considerable. The ravages of the other two families are 
happily almost entirely confined to insects, the larvae feeding especially 
on living caterpillars, and constituting an invaluable check on the 
numbers of the latter ; only in such a case as that of the silk-worm, 
which forms the prey of a certain Tachinid larva, is this most useful 
habit to be regretted by mankind, and in this case it is mankind’s own 
fault for domesticating the silk-worm. The few 41 biting ” flies among 
the family Muscidce have a very special interest in view of the part some 
at least of them play in spreading among men and animals diseases due 
to those minute blood parasites called “ Trypanosomes,” while the 
danger of infection of food with enteric and other germs, owing to the 
presence in kitchens and houses of flies which habitually settle on dung 
and other filth, though at present not fully realised, has been proved to 
be a real and serious one. 
