480 
Saw-flies, Gall-flies, Ichneumons, 
For example, the American tent-caterpillar has been found by Fiske (New 
Hampshire) to be attacked by twelve species. 
With regard to the number of parasitic individuals that may live at the 
expense of a single host individual no generalization can be made; the 
Fig. 676.—Hymenopterous parasites of a social-wasp. Fig. 1, nest of Vespa sp., portion 
of two envelopes cut away (two-thirds natural size); fig. 5, an adult parasite, 
Sphecophagus (?) predator, female; fig. 6, male of same species; fig. 10, Melittobia 
sp., female. (After Zabriskie; natural size indicated by lines.) 
number varies, Howard says, from 1 to 3000. From a single caterpillar 
of the cabbage-moth, Plusia brassica, 2500 individuals of the parasite Co pi- 
do soma truncatellum have been bred. From large hosts are often bred 
large numbers of parasites, but with some parasitic species only one or a few 
eggs are ever laid on a single host, whether it be large or small. Small hosts 
cannot, of course, provide food for many parasites and hence the number in 
