INDIRECT BENEFITS DERIVED FROM INSECTS. 189 



substance they inhabit ; for two species at least of Ichneumon} know how 

 to oviposit it in stercorarious larvae without soiling their wings or bodies. 



The ichneumonidan parasites are either external or internal. Thus the 

 species above alluded to, which attacks spiders, does not live within their 

 bodies, but remains on the outside^ ; and the larva of Ophion luteum, 

 which adheres by one end to the shell of the bulbiferous egg that produced 

 it, does not enter the caterpillar of Euprepia villica, the moth upon which 

 it feeds.^ But the great majority of these animals oviposit within the 

 body of the insect to which they are assigned, from whence, after having 

 consumed the interior and become pupae, they emerge in their perfect state. 

 An idea of the services rendered to us by those Ichneumons which prey 

 upon noxious larvae may be formed from the fact, that out of thirty indi- 

 viduals of the common cabbage caterpillar (the larvae of Pontia Brassicce) 

 which Reaumur put into a glass to feed, twenty-five were fatally pierced 

 by an Ichneumon (^Microgaster globatiis'^). And if we compare the 

 myriads of caterpillars that often attack our cabbages and brocoli with the 

 small number of butterflies of this species which usually appear, we may 

 conjecture that they are commonly destroyed in some such proportion — a 

 circumstance that will lead us thankfully to acknowledge the goodness of 

 Provideiice, which, by providing such a check, has prevented the utter 

 destruction of the Brassica genus, including some of our most esteemed 

 and useful vegetables. 



The parasites are not wholly confined to the order Hymenoptera : a 

 considerable number are also found amongst the tribe of flies, many of the 

 species of the Dipterous genera Tachina Meig. ; and those separated from 

 it (as Echinomyia Nemoraa, &c.), as well as of Anthrax, and other 

 genera depositing their eggs in caterpillars and other larvae, often in such 

 great numbers, that from a larvae of Sphinx atropos, bred by M. Serville, 

 and which had sufficient strength to assume the pupa state, not fewer than 

 eighty flies of Senometopia atropivora came out of it.^ Many beetles 

 also are parasitic in ibeir larvae state, as the singular Ripiphorus para- 

 doxus, which is found in the nests of wasps ; those of the genus Sitaris, 

 which are found in the nests of wild bees of the genus Anthophora^ ; and 

 those of Brachytarsus scabrosus, which feed on Coccidce'', he. 



' Ahjsia Manducator ; and another species allied to Alomyia Debellator, which I have 

 named A. Stercorator. « De Geer, ii. 863. ^ ibi,i_ 851—855. * Reaum. ii. 419. 



5 Macqnart, Dipteres, ii. 105. Comp. De Geer, i. 196. vi. 14. 24. Reaum. ii. 440—444. 



* Ann. Soc. Ent. de France, viii. Brit. xvii. xlvii. Much obscurity exists as to the econo- 

 my of these insects, chiefly in consequence of the curious facts observed by my friend M. 

 Pecchioli of Pisa with regard to his new species Sitaris solieri, described by him in the Attn. 

 Soc. Ent. de France, viii. 5. 27. He always found both sexes of this species, even in distant 

 localities, on plants of rosemary ; and these plants, when M. Audouin examined them with 

 him near Pisa in 1835, were covered with eggs, which the former recognized as altogether 

 similar to those of Sitaris hiimeraUs, with which he was well acquainted. As the species of 

 Sitaris are known to be found in the nests of different Hymenoptera, and particularly in 

 those of a wild bee [Anthophora) on the larvae of which their larvce are probably parasitic, 

 the question occurs, with what view the.se eggs were placed on the rosemary ? The most 

 plausible supposition perhaps would seem to be that after the eggs are hatched the larvae 

 attach themselves, like the supposed larvae of 3IeIoe {Pedic.ulus Melittce K.) to which they 

 are related, to the Anthop/wrce, frequenting the rosemary for honey, and are thus conveyed 

 into their cells ; but nothing certain can be inferred on this head till the contradictory state- 

 ments as to these last-named larvae are cleared up; and it seems as yet almost equally 

 doubtful, (as it is also in the case of the other parasitic coleopterous genera. Horia, Eipi~ 

 phorus, and Zonitis,) whether the larvae are parasitic on the larvae of the insects in whose 

 cells they are found, or on their stored-up food. 



'' Westwood, Mod. Class, of Ins. i. 332. 



