48 
of a primary parasite already containing eggs of the hyperparasitic 
Hem i teles ! 
The abundance of these Chrysopa cocoons in these situations does 
not, it seems to ns, prove that the larvae which constructed them had 
fed upon the Orgyia. It is more likely that they were attracted by the 
abundance of dipterous larvae, particularly of the larvae of the little 
Gaurax, although this is supposition only. 
The work of predatory Heteroptera was not especially marked, and 
in fact for some reason these insects do not seem to prey as extensively 
upon tussock-moth caterpillars as upon the fall webworm and other 
caterpillars. We have already called attention to the exemption from 
bird attack which this species possesses, and in fact the conspicuous 
coloration of the caterpillar seems to mark it as an especially protected 
form. 
(JEir^AL CONSIDERATIONS. 
Except for the remarkable number of species involved, there is 
nothing, perhaps, after all, so extremely unusual in the extensive case of 
parasitism of which we have just given the details. Wherever a plant- 
feeding species from some cause or from some combination of causes 
transcends its normal abundance to any great extent, there is always 
a great multiplication of its natural enemies, and this multiplication is 
usually so great as to reduce the species to a point even below its 
normal. Exceptions to this rule are seen with especially protected 
species, which, through the possession of some distasteful or repug- 
nant quality, have no predatory or parasitic enemies. Even in such 
cases, however, disease steps in and tills the want. I need only refer 
to the chinch bug as a familiar example of this class of injurious 
insects. It possesses no parasites, but when it increases beyond the 
bounds of what may be called nature's law, for want of a better term, 
bacterial and fungous diseases speedily carry it off. 
With all very injurious lepidopterous larv<T, however, we constantly 
see a great fluctuation in numbers, their parasites rapidly increasing 
immediately after the increase of the host species, overtaking it numer- 
ically and reducing it to the bottom of another ascending period of 
development. The unusual number of parasitic forms in the present 
case, however, and the extreme thoroughness of their work, as well as 
the plain evidence of the important part which hyperparasites have 
played, renders this particular case of perhaps more than usual interest. 
The culmination of the Orgyia attack may be placed at the end of 
August and early part of September, 189o. At that time almost every 
poplar, soft maple, box elder, elm, alder, birch, and willow in the city 
of Washington was completely defoliated, while other maples, syca- 
mores, horse-chestnuts, ashes, and many other trees were badly dam- 
aged. The rapidly developing parasites (some of them, as we have 
shown, requiring only two weeks for the development of an entire gen- 
eration) by this time had become so numerous that it was an exception 
