482 
Saw-flies, Gall-flies, Ichneumons, 
well marked, and we have come to rely on the effectiveness of the parasite spe¬ 
cies, Pimpla behrendsii, in overtaking by rapidly succeeding generations the 
increasing hosts of the pest, and in checking it before the actual realization 
of what is not infrequently threatened, the killing of all the live-oaks in 
certain regions of the state. 
An interesting phenomenon in the biology of these parasites is that of 
hyper parasitism. It frequently happens that the parasites of a given host 
are themselves parasitized by other (usually smaller) parasitic Hymenoptera, 
while even these secondary parasites are not infrequently parasitized in 
their turn by still other species. Indeed some 
cases are known in which the tertiary parasites 
are infested by a fourth or quaternary species. 
An excellent example of hyperparasitism is re¬ 
vealed by Fiske’s careful study, already referred 
to, of the hymenopterous parasites of the Ameri¬ 
can tent-caterpillar. Twelve species of parasitic 
hymenoptera infest these caterpillars; of these 
twelve, six are themselves attacked by parasites 
(secondary), of which as many as six species may 
Fig. 670 .—Ophion purga- v j . V ’ . . . . J . r . J 
turn, an ichneumon-para- attack a single species of the primary parasites. 
site of army-worms. (After Among these secondary parasites are not only 
Lugger, natural size.) species distinct from the primary parasites, but 
some of the primaries parasitize each other as well as the caterpillars. Of 
the secondary parasites, four species are in turn parasitized by other (ter¬ 
tiary) parasites, of which three species have been noted, one occurring also 
as a secondary parasite; and finally, one of these tertiary parasites is 
infested by another of the tertiary group, which in this instance becomes 
a quaternary parasite. Thus the old rhyme of 
“ Great fleas have little fleas 
Upon their backs to bite ’em, 
And little fleas have lesser fleas, 
And so ad infinitum ,” 
is often realized in the biology of the parasitic hymenoptera. 
Most interesting questions are suggested when we consider the unusual 
life-conditions that may, and often do, obtain in parasitism. Lying immersed 
in the blood-lymph of the body-cavity of the host, how does the parasitic 
larva breathe, excrete, moult, etc.? The process of feeding consists prob¬ 
ably for the most part simply in the taking up of the food from the host’s 
blood, in many cases probably as much through the skin, by osmosis, as through 
the mouth itself. With some species, however, there seems to be a definite 
