by Cold. Btj William Spence, Esq. 151 



number of insects which abounded the year before, if not to 

 frost ? I answer, that on this head we have yet much to 

 learn, but that one frequent cause is the multiplication of 

 the insect enemies, particularly those of the Linnean genus 

 Ichneumon, appointed to keep the noxious species within due 

 bounds. Birds do us great service in this way, but it is the 

 Ichneumon, that is our most valuable friend. Reaumur 

 relates, that in the autumn of 1735, when he examined a 

 great multitude of the common cabbage caterpillars, he 

 found that, out of every twenty-three, at least twenty-one 

 were filled with the grubs of Ichneumons, and consequently 

 doomed to infallible destruction.* A French gardener, who 

 observed in the spring of 1736, that the cabbage butterflies 

 were not one twentieth part so numerous as the cater- 

 pillars which infested his greens in the preceding year might 

 have led him to expect, would naturally give the credit of 

 destroying them to the winter, though evidently without 

 reason. 



At the same time, I am ready to admit, that severe win- 

 ters may be occasionally the indirect cause of the destruction 

 of some kinds of vermin, as in the case of the garden Shell- 

 snail (Helix Hortensis), which is said, in the newspapers, to 

 have been sought out last winter with such unusual dili- 

 gence by the thrushes, that in some places half a peck of 

 fragments of the shells lie round the stones to which these 

 birds brought them for the purpose of breaking them, and 

 getting at the snails. But besides that grubs, slugs, and most 

 caterpillars hybernate under ground, out of the reach of 



• Memoires, &c. torn. ii. p. 42. 

 VOL. II. X 



