318 
Proceedings of the Royal Society of Edinburgh. [Sess. 
described by Westwood* as typical of the Ichneumonid larvae: ; ‘two obliquely 
deflexed, horny mandibles, very small, slender, and acute, beneath which is a 
curved fleshy lobe, formed by the union of the dilated maxillae and labrum.” 
The fourth instar lasts one day. (Plate I, fig. 6.) 
The Fifth-Stage Larva. 
This differs in general shape from the fourth-stage larva. The 
abdominal region is now more swollen and the head region more pointed. 
This is probably accounted for by the fact that the alimentary canal is 
closed behind. The dorsal (prescutal) folds are also more marked and 
stand out in relief. The larva measures 6 '5 mm. Towards the end of the 
fifth stage, in the second day of its duration, the larva becomes yellowish 
in colour and commences to spin its cocoon. (Plate I, fig. 7.) 
The Cocoon. 
When the parasites are full fed their host is reduced to an empty sac, 
and the parasites now fill the cavity in the bark their host previously 
occupied. It is here they spin their cocoons. 
Just prior to spinning the larva becomes yellowish in colour. The first 
process in spinning is the enclosing and protecting of all the brood on the 
Hylobius larva. Each larva invests itself and its neighbours in a fine 
mesh of silk. Even isolated larvae spin this loose shawl-like covering 
before beginning the cocoon proper. This covering, however, does not 
completely enclose the larvae, for opposite the head of each a circular gap 
is left in the web. Each gap indicates the position of one end of the 
cocoon. The first covering is completed in a few hours, and in a few 
more the cocoons are so far constructed as to prevent further observation. 
In spinning, the larva sways its head to and fro, but the abdominal 
region remains stationary. Often the larvae are wedged between one 
another, but this in no way prevents each being enclosed in its own cocoon 
after the first covering is completed. The whole process rarely lasts 
twenty-four hours, and it is often completed in twelve. 
The cocoons are elongated and oat-shaped, blunt at both ends. The 
outer coating is of coarser texture and more hairy than the interior lining, 
and often is interwoven with tiny bits of grass or other material that may 
be lying in the tunnel cavity. At first the cocoons are silvery white, but 
in a day or so they become creamy, and finally yellowish, or even brown. 
(Plate II, fig. 15.) 
Inside the cocoon the larva remains quiescent until pupation. This 
* Westwood, Introduction to the Glassification of Insects, vol. ii, p. 147. 
