only a compai^ativi'ly sinnll number of g^enora are directly beneficial by 

 preying upon plant-lice, and even in this respect their services could 

 ill most instances be dispensed with, since, as a general rule, the plant- 

 lice are held in check by the larva' of ladybirds assisted by several 

 kinds of iuternal parasites belonging to the hymenopterous families 

 Braconida>, Cynipida», and Chalcidida\ 



So far as at present known the Tacliinida^ 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. Thdike 

 the parasitic Ilymenoptera, 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 si)eciesof Tachiua fly attacks 

 several different families of insects, while quite a number are known to 

 attack two and even three different orders of insects — Lepidoptera, 

 Ilymenoptera, and Coleoptera. This has been observed not only in our 

 own country but also in Europe. 



At present, only five different orders of insects — the three above 

 mentioned and the Orthoptera andllemiptera — are known to be attacked 

 by the TachinidiC in this country, but in Europe several cases are 

 reported of their also attacking Diptera of the family Tipulidic. 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 larvai usually enter tlie earth to pass 

 through their transformations. The larva' are of the usual maggot form, 

 large and truncated at one end and tapering to a point in the oi)posite' 

 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 

 oif its skin, rids itself of the egg before the latter has hatched out and 

 the young larva made its Avay into the body of the caterpillar. In this 

 respect the parasitism of these insects is not so certain as is the case 

 wdth those hymenopterous jiarasites which punctirre 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 flies appear to be far behind the parasitic 

 Hymenoptera. Tlie latter seem to be able to ascertain by a touch of 

 their antenna? whether or not an insect has already been parasitized, 

 and only rarely insert an egg in the body of an insect that already 



