294 BRITISH ICHNEUMONS. \Exetastes. 



effects its escape through a subcircular hole, a Httle on one side of the 

 apex ; if, however, through lack of oral fluid, etc., it is unable to emerge, 

 it reverses its position in the cocoon ( probably in the hope of finding 

 the other extremity more malleable), protrudes its tarsi from the incom- 

 plete orifice, and invariably dies in this position. After cutting its way 

 through all its envelopes, the imago rushes out at a great pace, with its 

 wings already quite fully developed and usually capable of instant flight, 

 though in weak cases they are damp or dabbled with pupal fluid. 

 They do not quit their cocoon as soon as the pupal state is terminated, 

 but several days are subsequently spent within it, during which the ulti- 

 mate state of perfection is attained. 



The host-caterpillar is consumed before attaining the pupal state, as is 

 evidenced by forty detached larval skins sent with, and thirteen actually 

 attached to the cocoons, among the thousand which have passed through 

 my hands. The parasitic larvae probably evacuate their hosts while 

 the latter are passing the daytime underground and there spend the 

 winter, since they are usually found during the digging of potatoes in 

 October and November. I have only once known a single 9 to emerge 

 in the autumn, but this was certainly accidental. The normal period is 

 from June isttojuly 22nd (for elaborate details of emergence cf. my 

 paper on this species, E.M.M. 1Q03, pp. 157-164). A great number of 

 the larvae are destroyed during the winter by mould, which attacked in 

 one batch thirty-two in five hundred and fifty ; a hyperparasitic Ichneu- 

 monid, Mesochorus viandibidaris, Thorns., rarely also M. fhoracicus, Grav., 

 devour about twenty per cent., and a species of Chalcid is also found in 

 the cocoons but I am of the opinion that this confines its slaughter to the 

 Mesochori ; and a few more fail to emerge through causes which are at 

 present obscure, possibly natural ailments."" 



* Some further details respecting this species may be of value from a biological aspect, since we 

 know so little of the economy of the Ichneumonidae. Wigin sent me (7 x 99) 398 cocoons, of which 

 one was malformed and proved abortive ; from another one ? Exetastes cinctipes emerged on the 

 loth ; and from a third one ? , presumably hyper-parasitic, Mesochorus thoracicus, Grav., had emerged, 

 with its wings dry, at g.30 p.m. on 14th of the same month. Wigin next sent (18 xi 99) 172 cocoons, 

 some oi which, however, were already empty. From these two consignments, I found there had 

 emerged, since the 6th, 26,} i and 3 ? ? Exetastes and one Mesochorus mandibularis (f by the i8th 

 of the following June, proving that the d" ^ emerge first; both sexes continued to emerge daily till 

 July 5th when the cf J',and 8th when the ? ?, fell off; though 5 more ii and 2 ? ? emerged 

 between 12th and iSth July: in all 184 cT J and 177? ? emerged. Thirty-two of the hyperparasitic 

 M. mandibularis <3 cf continued to emerge regularly till 15th of July, though most commonly from 4th 

 to 8th of that month ; but only 5 ? J emerged in all between 2gth June and i8th July. Thirty-two 

 specimens of some species of Pi^roHd/iis also emerged. Hence of the above 570 cocoons, 401 pro- 

 duced perfect Hymenoptera and in others I found 9 cf cf and 8 ? 9 perfect but dead Exetastes. Of 

 the remaining cocoons 31 had been slain by P^t'ra»irt/j (in one the Chalcid larvae still remained in 

 Oct. igoo, and were still soft); in 6 the larvae were found to have died of mould (one of these larvae 

 very plainly showed the hyperparasitic Mesochorus larva within it); 6 larvae had died from obscure 

 causes— probably the jars of transit ; 8 perfect Exetastes, of equal sexes, died unemerged ; one nearly 

 fully formed imago had died of mould and one only half formed imago had died from obscure causes. 

 Upon these cocoons I made the following notes: — (i) When the imago fails to emerge after attaining 

 maturity it is generally found to be attached to its cocoon by its anal extremity, though in one case 

 it was the wing that held it prisoner ; more rarely the insect succeeds in boring an exit hole insuffi- 

 cient for its emergence, when small this may be mistaken for that of a Chalcid, though its size 

 varies. (2) Sometimes, when the larva has been killed by mould, it occupies the whole cocoon and 

 at others it is much shrivelled, occupying only one-third of it, which is probably due to the period of 

 its growth at which the mould attacked it— though always, of course, full fed. (3) Whether the 

 Chalcids attack Exetastes or Mesochorus, I am uncertain, but from the size of the half-formed Ichneu- 

 mon (which is not sufficiently developed to allow of its distinctions bemg defined) and the punctura- 

 tioii of the pleurae, I am inclined to prefer the latter. (4) The Chalcids almost invariably emerge 



