INDIRECT BENEFITS DERIVED FROM INSECTS. 155 
Generally speaking, parasitic larvee do not attack insects in their perfect 
state ; but to this rule there are several exceptions, M. Dufour found in 
a beetle (Cassida viridis) a parasitic larva, from which he bred a.fly of the 
genus Lachina Meig. (Cassidemyia Macq.) ; and also in a field-bug (Pen- 
latoma grisea), from which proceeded another fly (Ocyptera 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 larve of a beetle (Simbius Blattarum) 
is parasitic in the bodies of Blatta Americana on board of ships, and 
M. Audouin found Coccinella 17-punctata, to be subject to the parasitic 
attack of Microctonus terminalis Wesmael, and Encrytus flaminius 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 formed 
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 Sphea) ; the second in the genus 
separated from Melitta K. under the name of Andrena, 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 hymenopterous insects will be found to be infested with them.* 
plants, when M. Audouin examined them with him near Pisa in 1885, were covered 
with eggs, which the former recognised as altogether similar to those of Sitaris hu- 
meralis, 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 Geesiog ate) on the larve of which their larvae 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 
larvae attach themselves, like the supposed laryw of Meloe (Pediculus Melitta K.) to 
which they are related, to the Anthophora, frequenting the rosemary for honey, and 
are thus conveyed into their cells; but nothing certain can be inferred on this head 
till the contradictory statements as to these last-named larve are cleared up; and 
it seems as yet almost equally doubtful (as it is also in the case of the other para- 
sitie coleopterous genera Horia, Ripiphorus, and Zonitis) whether the larve are para- 
nie on the lary of the insectsin whose cells they are found, or on their stored-up 
‘ood. 
7 Westwood, Mod. Class. of Ins. i. 832. 
1 Macquart, Dipteres, ii. 69. 
2 Thid. ii. 23. estwood, Mod. Ulass. of Ins. ii. 561. 
5 Westwood, Mod. Class. i. 295. 397. 
4 Kirby, Mon. Ap. Ang. ii. 110. 113. and in Linn. Trans. xi. 86. Westwood’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 oceur. My friend G. H. 
K. Thwaites, Esq.,, has had the singular good fortune, which has perhaps oc- 
curred to no other entomologist, of seeing on the wing in May, 1888, not merely 
4 single stylops or two, bul 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 probably owing to the circumstance of the garden hay- 
ing had brought into it a quantity of fresh earth, which apparently had been dug 
