INDIRECT BENEFITS DERIVED FROM INSECTS. 267 



compare the myriads of caterpillars that often attack our 

 cabbages and brocoli with the small number of butter- 

 flies of this species which usually appear, w,e may con- 

 jecture 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 

 Hymenoptera : some insects of other orders, though com- 

 paratively very few, destroy our little enemies in the 

 same way. Musca Larvdrum, and another like it de- 

 scribed by De Geer, lay their eggs in caterpillars and 

 other larvae a ; and Reaumur describes several other flies 

 of similar habits b . The order also of Strepsiptera, lately 

 established , appears to be altogether parasitic; but 

 with this difference from the Jchneumoniche, that these 

 extraordinary animals are found only upon Hijmenoptcra 

 in their perfect state, and do not appear to destroy the 

 insects upon which they prey, but probably prevent their 

 breeding. The species at present known are formed 

 into two genera, Xenos and Stylops, which are confined 

 to Melitta d and Vespa e . 



The next description of insect destroyers are those 

 which devour them in their jirst and last states. — No 

 beetles are more common after the summer is confirmed, 

 than the species of the genus Cantharis. Preysler in- 

 forms us that the grub of C.fusca destroys a great many 



a De Gcer, i. 196. vi. 14. 24. h Rcaum. ii. 440-4. 



c Linn. Trans, xi. 86. d Kirby's Mon. Ap. Ang. ii. 110-113, 



c Rossi Fn. fflrusc, Mant, 



