346 The Two-winged Flies 
and pupating with its fatal parasites still feeding inside. But the butterfly 
never issues: in its place buzz out several of these bristly Tachina-flies. 
While their habits arouse our indignation at first acquaintance, and par¬ 
ticularly if we have set our hearts on rearing a rare moth or butterfly, a 
moment’s reflection assures us of the immense good these flies must really 
do. Howard tells of an instance observed by him where the buzzing of 
the swarms of Tachina-flies, hovering over and laying their eggs on the 
hosts of a great army of army-worms, could be heard for a long distance. 
Fig. 491. Fig. 492. 
Fig. 491.—A Tachina-fly, Dejeania corpulenta. (One and one-half times natural size.) 
Fig. 492.—Tachinid parasite (at left) of the California flower-beetle, and parasitic fungus, 
Sporotrichum sp. (at right) of same beetle. (Slightly enlarged.) 
He says that a great outbreak of army-worms in northern Alabama in 1881, 
when all crops were threatened with total destruction, was completely frus¬ 
trated by Tachina-flies. These parasites also attack locusts, leaf-eating 
beetles, and many other injurious insects besides caterpillars, and altogether 
do much to keep in check some of our worst insect-pests. A single species 
of Tachina-fly (Fig. 492) is almost the only check on the destructive flower¬ 
eating Diabrotica ( D . soror) of California, which, if allowed to increase 
unhindered, would soon destroy every blossom in this land of flowers. 
Resembling somewhat in appearance the Tachina-flies are the so-called 
nimble-flies, constituting the small subfamily Dexiinae. Most of the species 
in this country belong to the single genus Dexia and have been little studied. 
The larvae seem to be all parasitic, although the life-history of no species has 
been wholly worked through yet. Beetles and snails seem to be the favorite 
hosts of these flies. 
In the large group of flies, some dingy and obscure in coloration, others 
brightly colored and with beautifully patterned wings, but all small and 
most unfamiliar, called the Acalyptrate Muscidae (that is, the house-fly 
allies with small alulets), we shall not attempt to distinguish the vari¬ 
ous subfamilies as we have for the Calyptrate Muscids. Dipterologists 
