Our knowledge of the special perils which beset particular species is so incomplete that we are often at a loss for the reason of this great inequality in fertility. For instance, how does _Synageles picata_ maintain its numerical strength by laying only three eggs, when, as M‘Cook points out, its resemblance to the ant, though advantageous to the adult spider, affords no protection to the egg? Our knowledge must be greatly extended before we are able to account for particular cases. Many influences hostile to spiders as a group are, however, well known, and we may here enumerate them. =Natural Enemies.=—The precautions taken by the mother in constructing the cocoon render the inclemency of the weather very much less destructive to the eggs than to the newly-hatched young. Nevertheless, among spiders inhabiting swampy regions great havoc is wrought by the occasional wholesale swamping of the cocoons by floods. Professor Wilder considers the great fertility of _Nephila plumipes_ necessary to counterbalance the immense destruction worked by the heavy rains upon their cocoons, which are washed in great numbers from the trees, to the leaves of which they are attached. But such exposed situations are avoided by many species, and their eggs, enclosed in 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 _Transactions of the Entomological Society_ for 1860, describes two species, _Hemeteles fasciatus_ and _H. formosus_, which are parasitic on the eggs 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 convenient 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.