194 ASSOCIATION OF ORGANISMS—THE WEB OF LIFE 
kind of life-history as the form last described, and are parasitic on 
bees of the same sort. The female beetle does not, however, lay 
her eggs near a suitable nest, but simply deposits them in the 
ground. The six-legged larve climb up various plants, and com- 
monly lie in wait on or near their flowers, attaching themselves 
at random to any hairy insects that come near enough. The 
chances of a given larva reaching a suitable destination are ex- 
ceedingly small, but as a set-off against this each female beetle 
lays some 10,000 eggs, which allows for considerable wastage. 
MEMBRANE-WINGED INSECTS (HYMENOPTERA) AS PARASITES.— 
Among the most interesting members of this order in the present 
connection are the Ichneumon-Flies, and other forms of similar 
habits, in which the female is provided with a sharp ovipositor, 
Fig. 1139.—The Yellow-Legged Ichneumon-Fly (Microgaster glomeratus). a, Adult; 0, tarva; c, dead caterpillar 
of Cabbage-Butterfly, surrounded by cocoons of the Ichneumon, Size of a and 4 indicated by the short lines. 
by means of which she deposits her eggs within the bodies of 
the larve, pup, or even eggs of other insects. In some cases 
deposition takes place not in, but on or sufficiently near, suitable 
victims. The early stages of Butterflies and Moths are particu- 
larly: liable to such attacks, and in this way the ravages of many 
of our familiar agricultural and garden pests are kept within 
bounds. Some of these parasites are in turn similarly attacked 
by insects not distantly related to them, a case of the biter bit. 
The common Cabbage-Butterfly (Pzevzs brassice) is subject to 
the attentions of a number of these forms. By one (Polynema 
gracilis) its eggs are pierced, two others (AZicrogaster glomeratus, 
fig. 1139, and Prmpla instigator) lay their eggs in its caterpillars, 
and still another two (Pleromalus puparum and P. pontie) attack 
its chrysalides. 
Certain larvee and pupze, that live where one would expect 
them to be quite secure from these parasitic insects, are never- 
theless sought out by them, and exposed to the murderous 
assaults of their brood. One kind of Ichneumon-Fly (Agriotypus 
armatus) boldly plunges into water, and lays her eggs in the 
