bo 
Or 
THE Cocoon. 
Directly after it has become full-fed, the grub forms a cocoon.+ 
As a rule the species that nest underground have the tougher 
cocoons ; they may be composed of from one (Dolichurus, Epyr is ) 
to many separable layers of silk (Methoca). Other cocoons may 
be formed of particles of sand, wood-dust, etc., agglutinized by 
means of the grub’s saliva into a tough shell (Bembex, Larra). 
The mud-daubers, already protected in a thick cell of mud, make 
a tough but very thin cocoon; so also with the mud-using 
Psammocharidae. It is noteworthy, however, that the parasitic 
Psammocharids, Ceropales, spin stout cocoons, even when occupy- 
ing the mud cells of Pseudagenia. Might this indicate that they 
were formerly burrowing wasps? The cocoons of Pseudagenia 
are thinner than those of their ground-nesting relatives that have 
to resist the moisture. Some Eumeninae make a thin but rather 
tough cocoon ; others, however (some Zethus), merely construct a 
thin leather-like partition which extends from near the top to a 
short distance down the sides of their cells. Several species at least 
of Stenogaster make no cocoons, but coat their cell with a shiny 
substance. Some wasps, of the family Pemphredonidae, are said 
to spin no cocoons. (Green, 1902.) The inner wall of the 
cocoon is smooth and varnished. Cocoons usually taper more 
at the posterior extremity, wherein the larva voids for the first 
and last time the contents of the intestine. There is some ad- 
vantage in this, as the cell is kept comparatively clean during the 
feeding stage, while later the walls of the cocoon readily absorb 
the moisture of the faeces which gives that end its characteristic 
color. Before spinning the body of the cocoon the larva usually 
makes a sort of scaffolding of silken strands to support it. The 
cocoon is commonly simple, but in some cases one end or even 
the side may be provided with a collar, knob or chamber (Me- 
thoca, Dolichurus, Epyris) 
The larva now encased within its cocoon has a resting period 
therein; this may be a question of a few days or of many months, 
for it is thus that solitary wasps usually pass the winter or the 
dry season.* The resting larva is usually more yellowish than 

yA few make no cocoons. 
* A rare exception, at least in temperate regions, is cited by Fabre in the case 
of a caterpillar wasp, Ammophila hirsuta Kirby, which hibernates as a full-grown 
wasp and in consequence begins nesting operations at a much earlier date than do 
related species. Davidson (1899), in speaking of Sphex elegans of Southern Cali- 
fornia, says that the majority of these wasps hatch out in July and August and 
pass the winter concealed in crevices, etc., and that probably not more than fifteen 
or twenty per cent remain in the larval stage until the following May. Bees very 
often hibernate as freshly-hatched adults. : 
