INDIRECT BENEFITS DERIVED FROM INSECTS. 269 



inur put into a glass to feed, twenty-five were fatally 

 pierced by an Ichneumon (/."/o/^^/Zi/^''). And if we com- 

 pare the myriads of caterpillars that often attack our 

 cabbages and brocoli with the small number of butter- 

 flies of this species that usually appear, we may conjec- 

 ture that they are commonly destroyed in some such 

 proportion — a circumstance that will lead us thankfully 

 to acknowledge the goodness of Providence, which by 

 providing- such a check has prevented the utter destruc- 

 tion of the Brassica genus, including some of our most 

 esteemed and useful vegetables. 



The parasites are not wholly confined to the order 

 Ili/menoptera: some insects of other orders, though 

 comparatively very few, destroy our little enemies in 

 the same way. Musca Larvarurn, and another like it 

 described by De Geer, lay their eggs in caterpillars and 

 other larvae^ ; and Reaumur describes several other 

 flies of similar habits'^. The order also of Strepsi- 

 ptera^ lately established '', appears to be altogether pa- 

 rasitic ; but with this diiference from the Ichneumonidw., 

 that these extraordinary animals are found only upon 

 Hymenoptera in their perfect state, and do not appear 

 to destroy the insects upon which they prey, but proba- 

 bly prevent their breeding. The species at present 

 known are formed into two genera, Xenos and Stj/lops, 

 which are confined to Melilta'^ and Vespa^. : 



The next description of insect destroyers are those 

 which devour them in their j^r*^ and last states. — No 

 beetlesare more common afterthe summer isconfirmed, 



^ Reaum. ii. 419. " De Geer, i. 196. vi. 14. 24. 



" Keaum. ii. 440-4. * Linn, Trans, xi. 86. 



' Kirby's Mon. Ap. Aug. ii. 110-113. ' Rossi Fn. Elnisc. Mant. 



