INDIRECT BEls'EFITS DERIVED FROM INSECTS. 155 



Generality speaking, parasitic larvae do not attack insects in their perfect 

 state ; but to this rule there are several exceptions. M. Dufour found in 

 a beetle {Cassida viridh) a parasitic larva, from which he bred a riy of the 

 penus Tachina Meig. (CassidcEmi/ia Macq.) ; and also in a field-bug {Pen- 

 tutoma grisea), from which proceeded another fly (Oci/ptera bicolor)^ ; and 

 Latreille, Dufour, and other entomologists have confirmed the discovery of 

 Baumhauer, that the larvae of flies of the genus Conops live in humble- 

 bees, which M. Robineau-Desvoidy has seen pursued by them, apparently 

 to deposit their eggs on them.'^ The larvae of a beetle (Simbius Blattariim) 

 is parasitic in the bodies of Blatla Americana on board of ships, and 

 INI. Audouin found CoccincUa \1 -jnnictata, to be subject to the parasitic 

 attack of Microctonns tenninaHs Wesmael, and EncrytusJlavnnius'DiAman.^ 



The order also of Slrepsiptera appears to be wholly parasitic ; but 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 

 probably prevent their breeding. The species at present known are formed 

 into four genera, Xenos Rossi , Stylops Kirby , Elenchus Curtis ; and 

 Halidophagits Dale. The first is found in different species of wasps 

 ( Vespa, Polistes, Odynerus, and also of Sp/ie.r} ; the second in the genus 

 separated from Melitta K. under the name of AndrcEiia, in upwards 

 of fourteen species of which Mr. Pickering has found them ; the third in 

 Polistes (?) ; and the fourth in Halictus {Melitta K.) ; but it is probable, 

 from the fact of JM. L. Dufour's having also found a larva of one of these 

 insects between the abdominal segments of Ammophila Sabiclosa, that many 

 other hymenopterous insects will be found to be infested with them.'* 



plants, when M- Audouin examined them witli him near Pisa in 1835, were covered 

 with eggs, which tlie former recognised as altogether similar to those of Sitaris hu- 

 me.ralis, with which he was well acquainted. As the species of Sitaris are known to 

 be found in the nests of different H3'menoptera, and particular]}' in those of a wild 

 bee (^Anthophora^ on the larva; of which their larva; are probably parasitic, the ques- 

 tion occurs, with what view these eggs were placed on the rosemary.' The most 

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

 larviB attach themselves, like the supposed larvaj of Meloe (Pediculus 3Ielitt(B K.) to 

 Avhich the)' are related, to the Antliophora, frequenting the rosemary for honey, and 

 are thus convej-ed into their cells; but nothing certain can be inferred on this head 

 till the contradictory statements as to these last-named larva; are cleared up ; and 

 it seems as yet almost equally doubtful (as it is also in the case of the other para- 

 sitic coleopterous genera Horia, Ripiphorus, and Zonitis) whether the larvae are para- 

 sitic on the larvas of the insects in whose cells they are found, or on their storod-up 

 food. 



7 Westwood, 3Iod. Class, of Ins. i. 332. 



1 Jlacquart, Dipteres, ii. 69. 



2 Ibid. ii. 23. Westwood, Mod. Class, of Ins. ii. 561. 



3 Westwood, Mod. Class, i. 295. 397. 



4 Kirby, 3Ion. Ap. Ang. ii. 110. 113. and in Linn. Trans, xi. 86. Wcstwood's 

 Mod. Class, of Ins. ii. 288—305., to which last the reader is referred for a full and 

 very interesting account of the facts hitherto recorded respecting these remarkable 

 insects, and references to the various works in which they occur. My friend G. H. 

 K. Thwaites, Esq., has had the singular gcod fortune,' which has perhaps oc- 

 curred to no othei entomologist, of seeing on the wing in May, 1838, not merely 

 a single stylops or two, but a small swarm of at least twenty, and in as singular a 

 situation, the garden of his residence, situated in the suburbs of the populous city 

 of Bristol. This was most probiibly owing to the circun-.stance of the garden hav- 

 ing had brought into it a quantity' of fresh earth, which apparently had been dug 



