8 
only a comparatively small number of genera are directly beneficial by 
preying upon plant lice, and even in this respect their services could 
in most instances be dispensed with, since, as a general rule, the plant- 
lice are held in check by the larvae of ladybirds assisted by several 
kinds of internal parasites belonging to the hymenopterous families 
Braconidae, Cynipidae, and Chalcididae. 
So far as at present known the Tachinidae prey upon living insects 
only, and by far the greater number of these are the leaf-eating cater- 
pillars of butterflies and moths, a group that contains a large number 
of our most injurious insects: and the numbers of these destroyed in a 
single season by these parasites is almost beyond computation. Unlike 
the parasitic Hymenoptera, each species of which as a rule confines its 
attacks to a single group which in some cases is restricted to one genus, 
it not infrequently happens that the same species of Tachina fly attacks 
several different families of insects, while quite a number are known to 
attack two and even three different orders of insects — Lepidoptera, 
Hymenoptera. and Coleoptera. This has been observed notonly in our 
own country but also in Europe. 
At present, only live different orders of insects — the three above 
mentioned and the ( hthoptera and Hemiptera — are known to be attacked 
by the Tachinidae in this country, but in Europe several cases are 
reported of their also attacking Diptera of the family Tipulidae. The 
Lepidoptera, Hymenoptera, and Diptera are preyed upon in their pre- 
paratory stages only, whereas it is usually only the adults of the 
Orthoptera, Hemiptera. and Coleoptera that are attacked. 
The tachinid eggs are attached by a viscid substance to the surface 
of the host, and the full grown larvae usually enter the earth to pass 
through their transformations. Hie larva- are of the usual maggot form, 
large and truncated at one end and tapering to a point in the opposite 
direction. Pupation takes place in the hardened skin of the larva, which 
assumes a nearly cylindrical form with rounded ends, and is known as 
a puparium. In issuing, the adult fly breaks away the entire end of 
the puparium. It was formerly supposed that any caterpillar upon 
which one of these flies had fastened an egg was doomed to certain 
destruction, but actual observation has shown that this is not always 
the case, since in many instances the caterpillar, by molting or casting 
off" its skin, rids itself of the egg before the latter has hatched out and 
the young larva made its way into the body of the caterpillar. In this 
respect the parasitism of these insects is not so certain as is the case 
with those hymenopterous parasites which puncture the body of their 
victim and deposit the egg within. 
In regard to the possession and exercising of that faculty commonly 
termed instinct, the Tachina Hies appear to be far behind the parasitic 
Hymenoptera. The latter seem to be able to ascertain by a touch of 
their antenna 1 whether or not an insect has already been parasitized, 
and only rarely insert an egg in the body of an insect that already 
