PARASITE-INSECTS. 63 



But it is not only in the nests of bees and wasps, 

 or in the bodies of caterpillars, that these provident 

 mothers contrive to deposit their eggs ; for many of 

 them are so very minute, as to find in the egg-s them- 

 selves of larger insects a sufficient magazine of ibod 

 for their progeny ; and accordingly, piercing the shell 

 with their ovipositor, they thrust their own into the 

 perforation. The most common instance of this 

 which we have remarked occurs in the eggs of 

 spiders ; patches of which may be found almost 

 everywhere under the cross bars of palings, and the 

 copings and corners of walls. Though spiders, for the 

 most part, not only cover their eggs with a thick 

 envelope of silk, but also remain near to protect them 

 from enemies, yet a small four-winged fly (Cryptus, 

 Fabr.), and, if we are not mistaken, two-winged flies 

 {Muscid(Ey Leach), also, outbrave the danger of being 

 caught and immolated by the mother spider, and 

 introduce their eggs either into or among those of 

 their powerful enemy. These spider's eggs are 

 subsequently feasted upon by the progery of the 

 flies, — a very natural reprisal for the ravages com- 

 mitted by this carnivorous race upon the whole gene- 

 j ration of their fellows. That the mother flies actually 

 ■I pierce the eggs of other insects was observed before 

 I! the year 1730, by the accurate Vallisnieri, who says, 

 I '* I have seen with my own eyes a certain kind of 

 \ wild flies deposit their eggs upon other eggs, and 

 [l bore and pierce others with an ovipositor {acnUusi)^ 



!j by means of which they have introduced the egg*." 

 j Count Zinanni, another Italian naturalist, told Reau- 

 j mur, that, his attention being attracted by a small 

 fi ichneumon fluttering about the eggs of butterflies, 

 1.} he soon observed it alight and fix upon one of these 

 |i eggs; and, without being incommoded by his ol)- 

 \[ serving her proceedings through a strong magnitier, 

 ; * Vallisnieri, I.elteie, 80. 



