THE HYMENOPTERA. I 85 
an end also. It is only when the larva is nearly full grown, and is 
about to undergo its metamorphosis into a pupa, that it appears 
to know that the life of the victim is not likely to be of much 
further use. It then devours the internal organs of the unfor- 
tunate insect, and undergoes its transformation. The skin of 
the victim protects some of the pupe of its destroyers after 
all the inside has been eaten. 
Nearly all—if not quite all—insects are subject to the attacks 
of parasitic Hymenoptera. Fine, smooth, and_brightly-coloured 
caterpillars often have a black spot upon their skin, and this is 
the healed wound of the ovipositor of one of the parasites. 
Sooner or later the creature is sure to die, and it never reaches 
the stage of growth when it can lay eggs or reproduce its kind, for 
before this time the growing larva within destroy it, as it were, by 
a slow consumption. Some affected caterpillars die soon, others 
nearly reach their full growth, and a few undergo their transforma- 
tion into the chrysalis state before death. It is, therefore, not an 
uncommon thing for a butterfly collector, who hopes to see a fine 
moth disengage itself from its pupal covering, to be disappointed 
by the appearance of several little parasitic //ymenoptera that 
have been living within the chrysalis he has been keeping. 
Although we know a great deal about the economy of the 
parasitic Hymenoptera, still there are some points of the greatest 
possible interest in it, and which are really very provocative of 
wonder. When a parasitic insect of this family discovers a cater- 
pillar feeding on a leaf in broad daylight, there is nothing very 
wonderful about it, because we could do as much ourselves; but 
when it is evident that the female parasitic Yymenoptera finds out 
a larva which is situated inside a fruit, and within a branch or 
trunk of a tree, and perfectly out of sight, we may well wonder 
how this is done. When one sense fails, another is supposed to 
supply its place, and the sense of smell of the insect is thought to 
do what the eyes evidently cannot perform. It is probable that the 
sense of hearing may assist in the discovery, but it is by no means 
proved. There is another instinct which is very remarkable, and, 
indeed, as curious as that just mentioned. A large parasite deposits 
only one egg under the skin of a caterpillar or other insect, for 
its) larva, as it increases in» size; requires.(all. the. jwices of the 
