190 INDIRECT BENEFITS DERIVED FROM INSECTS. 



Generally 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 vh'idls) a parasitic larva, from which he bred a fly of 

 the genus Tachina Meig. (^Cassidamyia Macq.) ; and also in a field-bug 

 (Pentatoma grised), from which proceeded another fly (^Ocyptera hicol- 

 ory ; 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 (^Simhius 

 Blattarum) is parasitic in the bodies of Blatta americana on board of 

 ships, and M. Audouin found Coccinella ll-punctata, to be subject to the 

 parasitic attack of Microctonus terminalis Wesmael, and Encrytus Jiami- 

 nius Dalman."^ 



The order also of Strepsiptera 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 form- 

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

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

 (Vespa, Polistes, Odynerus, and also of Sphex) ; the second in the genus 

 separated from Melitta K. under the name of Andrcena, 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 M. L. Dufour's having also found a larva of one of these 

 insects between the abdominal segments of Ammophila Sabulosa, that 

 many other hyrnenopterous insects will be found. to be infested with them."* 



The next description of insect destroyers are those which devour them 

 in their ^r^^ and last states. No beetles are more common after the sum- 

 mer is confirmed than the species of the genus Telephorus. Preysler in- 

 foms us that the grub of T. fuscus destroys a great many other larvas^ ; and 

 I have observed the imago devour these and also Diptera. Linne has 

 with justice denominated the Cicindela the tigers of insects. Though 

 decorated with brilliant colors, they prey upon the whole insect race ; their 

 formidable jaws which cross each other are armed with fearful fangs, show- 

 ing to what use they are applicable ; and the extreme velocity with which 



> Macquart, Dipteres, ii. 69. ^ Ibid. ii. 23. Westwood, 31od. Class, of Ins. ii. 561. 



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



* Kirby, Mon. Ap. Ano. ii HO. 113. and in Linn. Trans, xi. 86. Westwood's Mod. Class. 

 of Ins. ii. 288—305., to vvhich last the reader is referred for a full and very interesting ac- 

 count 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 good fortune, which has perhaps occurred to no other entomologist, of seeing on 

 the wing in May, 1838, not merely a single stjjlops or two, but a small swarm of at least 

 twenty, and iu as singular a situation, the garden of his residence, situated in the suburbs 

 of the populous city of Bristol. This was most probably owing to the circumstance of th? 

 garden having had brought into it a quantity of fresh earth which apparently had been dug 

 from some bank or pathway, containing many of the nests of Andrena convexiusciila, which 

 also abounded in the garden at the same time, and of which Mr. Thwaites captured several, 

 all containing the larva of a Stylops (in one instance of three), or evident signs of a Stylops 

 having escaped from them. These singular little animals, whose economy and systematic 

 place are equally perplexing, Mr. Thwaites informs us " are exceedingly graceful in their 

 flight, taking long sweeps as if carried along by a gentle breeze,'' which, and their large 

 expanse of wing, give them an appearance in flying very different from that of any other 

 insect. (Thwaites in Trans. Ent. Soc. Land. iii. 67.) 



* Preys. BOmisch. Insekt. 59. 61. 



