650 
DIPTEKA. 
rather indistinct. Sometimes the caterpillar dies under this treatment 
before it can pupate, but very often the pupal stage is reached. The 
Tachinid larva when full fed generally leaves the body of its host (which 
then always dies) and pupates in some sheltered spot, usually just 
below the surface of the ground. Most of the Sarcophagidce and 
Muscidce also habitually pupate one or two inches deep in the earth near 
the place where their larval stages were passed through. Unlike most of 
the parasitic Hymenoptera , Tachinidce do not seem necessarily to confine 
themselves to particular hosts, and one species of Tachinid may lay eggs 
on caterpillars of several different species indiscriminately. They also 
not infrequently make the mistake of laying eggs on a caterpillar which 
is already attacked, and in such cases many of the larvae must necessarily 
be starved, since the caterpillar can provide food only for a limited 
number : similarly in the nests of Hymenoptera which store spiders, 
too many Tachinid larvae are sometimes found, the supply of spiders, 
being insufficient for all, so that some die or are eaten by their fellows. 
Again, eggs are sometimes laid just before a moult, and if the cater¬ 
pillar can cast its skin before the Tachinid larvae hatch it will of course 
escape and the larvae will die. Among the parasitic Hymenoptera 
such mistakes and irregularities as these are very rare, the life of the 
parasite being generally arranged so as exactly to correspond to, and 
as it were fit into the weak places in, the life-history and habits of its 
host. As has been said already, it is possible that the Calyptrates are a 
group of comparatively recent development, and it may be that their 
imperfect adaptation to a parasitic mode of life is due to their having 
taken up this mode of life comparatively lately, their habits and 
instincts having not yet reached that precise adjustment which has been 
attained by many parasitic Hymenoptera. 
A recent very interesting paper by Townsend (U. S. Agric. Dept. 
“ Record of rearing Tachinidce ”) contains much new information on the 
varieties of oviposition and “ larviposition among Tachinids, and 
reveals considerable diversity among different species. He has made 
the curious discovery that certain American Tachinids do not lay their 
eggs on the caterpillars, but on the leaves, so that they are eaten by the 
caterpillar and hatch in its stomach, a method very similar in essentials 
to that followed by Gastrophilus among (Estridce . 
