8 
SOUTH-AFEICAN BUTTERFLIES. 
tion of cocoon wliicli they carry about with them, and from which only 
the head and front segments bearing the legs protrude. These silken 
fabrics are externally both strengthened and disguised by attached 
pieces of objects among which the larva lives, such as woollen tissue 
(in the case of the Clothes-Moth caterpillars), sand, small particles 
of stone, bits of grass, or sticks. In the case of many of the latter, 
the bits of grass or sticks are most neatly cut of the required length, 
and firmly secured in most regular order, the whole resembling the 
conventional fasczs of the Koman lictor. 
Caterpillars are, apparently, of all insect larvae the most liable 
to attack by the parasitic Hymenoptera, known as Ichneumon-flies 
(families Iclmeumonidce, ChalcididcB, &c.). The female fly is provided 
with an acute ovipositor, by means of which she pierces the caterpillar's 
integument, and introduces her eggs. The grubs of the Ichneumon-fly 
soon hatch in the caterpillar's body, and begin to devour its tissues. 
They appear to avoid injuring the vital organs, and to derive nearly all, 
if not the whole, of their sustenance from the spacious fat-body {corpus 
adiposum) which envelops the caterpillar's alimentary canal, &c., and 
fills almost all the space between those organs and the body-walls. The 
caterpillar so infested usually lives to attain its full size, and sometimes 
to assume the chrysalis form, but it never reaches the perfect state, its 
devourers either emerging to spin their own little cocoons around its 
skin, or undergoing their metamorphosis within it. Other deadly 
parasites are the species of Tacliina^ flies of the Order Diptera, which 
fasten their eggs on the surface of the caterpillar, into whose body the 
maggots hatched from them penetrate. 
There is much difference among caterpillars as regards activity 
of motion. Those of Butterflies are for the most part remarkably 
sluggish, scarcely moving except from one leaf to another, and those of 
the Hawkmoths and higher Bombyces are as a rule but little more 
active. Among the latter, however, the well-known hairy larvge of the 
lovely Tiger-Moths (Ardiidce) are an exception, being frequent and 
rapid walkers. The caterpillars of many of the lower groups of moths 
{Noduoe, Pyrales, Geometrce, and Tortrices) are very quick in their 
motions, a few even exhibiting the power of leaping away when dis- 
turbed. The Geometrce larvas almost invariably have only two pairs of 
" claspers " or pro-legs, situated posteriorly on the tenth and thirteenth 
segments, with which peculiarity is associated the mode of progression 
which led to their name ; this consisting of their stretching out the 
body forward and grasping with the true legs near the head, and then 
bringing up the pro-legs close to the others, so that the long inter- 
mediate legless portion of the body is looped or arched. In this way 
they proceed by long-measured steps, instead of by the continuous 
undulatory motion of caterpillars with the full complement of pro-legs. 
These Geometer larvae have in a great many instances the extraordinary 
power of keeping the body for hours rigidly extended from its base of 
