Predaceous Insects and their Prey. 397 
a predaceous Dipterous larva of such special interest that 
I determined to include it. 
Dr. T. A. Chapman (“ Ent. Mo. Mag.” 1905, pp. 150, 151 ; 
1906, pp. 14-16) has observed the larva of Xanthandrus 
comtus feeding upon Tortricid larvee, but only upon such 
as are gregarious or at any rate numerous upon their food 
plant. Hastula hyerana fulfilled this condition at Hyeres, 
Acroclita consequana in Sicily, and a larva, probably of 
Ancylis derasana in the Alps: in all these cases Dr. Chap- 
man found the larva of the Syrphid feeding upon that of the 
Tortricid. In Sicily H. hyerana occurred singly, and the 
Syrphid was not found attacking it.’ Dr. Chapman con- 
cludes from these instances that “X.comtus feeds especially 
on the larvee of Tortrices when there are many on a plant,” 
while “the isolation of the individual larve” renders them 
“an unsuitable prey for this parasite.’ The Syrphid larva 
would in fact “perish when it had destroyed its solitary 
prey and could find no others.” 
It is of the highest interest therefore to establish the 
fact, as Mr. G. T. Lyle of Brockenhurst has now done, that 
the larva of this species is found attacking single Lepi- 
dopterous larvee when they are large enough to provide 
sufficient food. 
In August 1903 Mr. Lyle found the full-fed Syrphid 
larva inside the shelter (constructed of sallow leaves 
loosely spun together) of the larva of the Geometrid moth, 
Scotosia undulata. Nothing remained of the latter except 
the dry and empty skin. The Syrphid larva was of a 
bright apple-green colour with darker markings. In 
September 1903 the perfect insect emerged. The speci- 
men, together with the empty globular puparium,* was 
presented to the Hope Department by Mr. W. J. Lucas to 
whom Mr. Lyle had given it. The fly, a male (309), was 
kindly identified for me by Col. J. W. Yerbury. 
Putting together Dr. Chapman’s and Mr. Lyle’s 
observations, there is reason for the opinion that the 
female Syrphid is instinctively led to deposit her eggs 
where there are either many minute larve or single 
larvee of sufficient size. The adaptation to two different 
conditions under either of which sufficient food may be 
provided is of much interest, and it is to be hoped that 
further observations will be directed to the subject, so that 
s See Dr, T. A. Chapman’s description in ‘‘ Ent. Mo. Mag.” 1905, 
p. 151. 
