262 



BRITISH ICHNEUMONS. 



\^Mesos/€tius. 



times the parasite consumes its host before the latter pupates, in which 

 case the remains of the caterpillar are pushed to the apex (i) and the next 

 cell (2) is empty and separated from the apical by a fragile partition erected 

 by the parasite before completing its own cocoon (3) ; this partition is 

 always present and divided from the parasite's cocoon by a more or less 

 broad space (2). The broader extremity of the host's cocoon is not 

 reached by that of the parasite, so that a little empty cell (4) is left between 

 them ; the apices of the parasite's own cocoon are very stout and their 

 surface uneven. 



The larva (see fig.) is onisciform, twelve millimetres in length and about 

 six in breadth in repose, deplanate, entirely primrose-yellow and diapha- 

 nous with numerous lighter, sub-cutaneous, opaque granules. It has a 

 fleshy lateral border containing the spiracles which are boldly marked by a 

 dot within a circle ; this border is distinctly discreted and, together with 

 the anal segment, sub-translucent. There are ten segments, of which the 

 head has the outlines of the mouth organs (see fig.) piceous and two 

 longitudinal frontal marks ferrugineous ; the remainder of the head is of 

 the same colour as, though more coriaceous than, the rest of the body, 

 the whole surface of which is covered with extremely close and extremely 

 minute punctures. The eight central segments are furnished dorsally with 

 pseudo-feet, the central ones being the most prominent and powerful. 

 When frightened the larva remains motionless with head retracted and 

 defiexed ; it has the power of closing a rent in its cocoon (in March) with 

 a perfectly white substance, and can withdraw at will into half the area of 

 its cocoon, which is curiously convex for so flat a larva. 



Before pupating the larva becomes less fleshy, more elongate, narrower 

 and darker in colour ; Moncreaff adds (Entom. iv. p. 125) that at the end 

 of January " the eyes become darker and numerous pellets of frass are 

 ejected." The pupa (see figg.) is somewhat light-yellow, with red eyes ; it 

 is of the usual Ichneumonid type and still retains its dorsal prolegs. It 



has the faculty of violently jerking the 

 cocoon by rapidly twisting round and round 

 upon the apex of its abdomen. I have found 

 that it does not become a pupa till quite the 

 end of March, but sometimes by the end of 

 February the waist is beginning to contract 

 and the antennae, legs and wings show 

 through the shell ; by the second week in 

 March the whole of the members stand 

 clear of the body, each encased in a trans- 

 parent covering ; next minute atoms of a 

 dark colour, commencing at the head, gradually steal over the body, 

 which in a short time assumes its perfect markings, and by the end of 

 March, in some cases, the insect is perfect. The antennae are then 

 drawn one by one from their cases, the legs and wings quickly follow, 

 the whole envelope is thrown off, and the perfect insect lies for some 

 time within its cocoon before emergence. 



Its final ecdysis usually occurs between dusk and midnight, and the 

 imago is extremely vivacious throughout the whole course of its life, 

 which, in the male, lasts only three or four days in confinement. I have 

 found them to emerge between May 15th and June i8th, the latest date 

 being July 3rd, and the males precede the females about eight days. 



Natural size. 



'\%\v 



