PARASITE INSECTS. 63 



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

 in the bodies of caterpillars, that these provident mo- 

 thers contrive to deposit their eggs; for many of them 

 are so very minute, as to find in the eggs themselves 

 of larger insects a sufficient magazine of food 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 re- 

 marked, 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 (Muscidce, LEACH), also, outbrave 

 the danger of being caught and immolated by the mo- 

 ther spider, and introduce their eggs either into or 

 among those of their powerful enemy. These spiders' 

 eggs are subsequently feasted upon by the progeny of 

 the flies, a very natural reprisal for the ravages 

 committed by this carnivorous race upon the whole 

 generation of their fellows. That the mother flies ac- 

 tually pierce the eggs of other insects was observed 

 before the year 1730, by the accurate Vallisnieri, who 

 says, ' I have seen with my own eyes a certain kind 

 of wild flies deposit their eggs upon other eggs, and 

 bore and pierce others with an ovipositor (aculeus), 

 by means of which they have introduced the egg.'* 

 Count Zinanni, another Italian naturalist, told Reau- 

 mur, that, his attention being attracted by a small 

 ichneumon fluttering about the eggs of butterflies, 

 he soon observed it alight and fix upon one of these 

 eggs ; and, without being incommoded by his ob- 

 serving her proceedings through a strong magnifier, 



* Vallisnieri, Lettere, 80. 



