XIV ENEMIES OF SPIDERS 367 
their silken envelope, are well protected against the severities of 
the weather. 
A more universal enemy to the egg is found in Ichneumon 
flies. On examining the cocoons of almost any species of 
spider, a large proportion are almost certain to be found to 
contain Ichneumon larvae. Mr. F. Smith, in the 77ransactions 
of the Entomological Society for 1860. describes two species, 
Hemeteles fasciatus and H. formosus, which are parasitic on the 
eges of Agelena brunnea They are figured in Mr. Blackwall’s 
book on British Spiders. Pezomachus gracilis attacks the cocoons 
of many kinds of American spiders, appearing to have no special 
preference for any particular species, while <Acoloides saitidis 
seems to pay special attention to the eggs of certain of the 
Jumping-spiders, and particularly of Saitis pulex. 
The Ichneumons which thus regard the Spider’s eggs as con- 
venient food for their own larvae are probably very numerous. 
Nor are they themselves always free from parasites. Occasionally 
the larvae of minute Hymenopterous insects are found to be 
parasitic upon the eggs of an Ichneumon which have been laid in 
a Spider’s cocoon. 
It sometimes happens that the development of the young 
spiders has so far advanced at the time of the Ichneumon’s 
intrusion that the latter’s intention is frustrated, and its offspring, 
instead of devouring, are themselves devoured. Again, some few 
of the eggs in an infested cocoon occasionally escape the general 
destruction and reach the adult condition, but there can be no 
doubt that Ichneumons are largely instrumental in keeping down 
the numbers of most species of spiders. The perils which attend 
the Spider after leaving the cocoon are no less formidable, and 
much more numerous. The whole newly-hatched brood may be 
destroyed by a heavy rain-storm. If there is not a sufficient 
supply of food suitable to their feeble digestive powers they 
perish of inanition, or eat one another. This cannibalistic pro- 
pensity is a considerable factor in the mortality among young 
spiders, and the adult animals frequently prey upon one another. 
Argyrodes piraticum, in California, invades the webs of larger 
spiders of the family Epeiridae, which it seizes and devours. A. 
trigonum, common in the eastern states of North America, has the 
same habit." Hentz found in Alabama a spider, which he named 
1 M‘Cook, f.c. p. 389. 
