CORRESPONDENCE, 
481 
Three Pup^: in one Cocoon. 
To the Editor of the Naturalist. 
Bear Sir, —As you state (p. 318) that the more you are “troubled” with 
queries, and seem to intimate that the less you are bothered with apologies for so 
troubling you, the better you will be pleased, I have taken it upon myself in the 
present instance to ask of you, or some of your correspondents, a little informa¬ 
tion. In 1837 I had two caterpillars of Acronycta Psi (the Dagger Moth), 
which feed upon the leaves of the Pear-tree, and in some seasons are rather 
abundant. These I kept in a small box, and in due time they enclosed themselves 
in their cocoons. Next Spring I cut open the cocoons, in order that the Moths I 
. expected might escape without injuring their wings, when to my surprise I found 
in one of them not one but three pupae. Having read in the Entomological 
Magazine of cases which I thought of a similar nature, and whose accuracy had 
been doubted, I was much pleased with my discovery. On opening the box some 
time after, I found not three Moths, as I was almost led to expect, but three 
Plies belonging to the genus Musca , and apparently a very common species. 
Never having, so far as I remember, seen it mentioned that Diptera were parasitic 
on the larva of Lepidoptera , and being anxious to know whether it was a com¬ 
mon circumstance, I stated the above facts to Mr, P. Rylands, who with the 
true spirit of a man of science (who always confesses his ignorance when he really 
knows nothing of the subject), says in a letter to me,—“ With respect to parasitic 
Diptera , I never myself met with a case, but friends have, and I have specimens 
of a Musca which I am informed was bred from some Moth. I do not know the 
species, not having paid much attention to Diptera .” A case similar to the 
above occurred during last Summer (with the same caterpillar) to my friend Mr. 
George Buist, in which, however, the Flies have not yet escaped from the pupa 
state. Perhaps Mr. Dale, or some other of your entomological correspondents, 
may be able to give me some information on this point; and by doing so will 
confer a favour on, 
Dear Sir, 
Sincerely yours, 
Law-Park Cottage , near St. Andrews, Henry Buist. 
April 12, 1839. 
