Scolia-grubs contrive at most to upholster
their little pit with a thick down of reddish silk. Discouraged by
futile endeavours, some of them die. It is as if they had been killed by
the silk which they omit to disgorge because they are unable to make the
right use of it. This, if we were not watchful, would be a very frequent
cause of failure in our attempts at artificial rearing. But, once the
danger has been perceived, the remedy is simple. I make a ceiling over
the cavity by laying a short strip of paper above it. If I want to see
how matters are progressing, I bend the strip into a semicircle, into
a half-cylinder with open ends. Those who wish to play the breeder for
themselves will be able to profit by these little practical details.

In twenty-four hours the cocoon is finished; at least, it no longer
allows us to see the grub, which is doubtless making the walls of its
dwelling still thicker. At first the cocoon is a vivid red; later it
changes to a light chestnut-brown. Its form is that of an ellipsoid,
with a major axis 26 millimetres in length, while the minor axis
measures 11 millimetres. (1.014 x.429 inch.--Translator's Note.) These
dimensions, which incidentally are inclined to vary slightly, are those
of the female cocoons. In the other sex they are smaller and may measure
as little as 17 millimetres in length by 7 millimetres in width. (.663
x.273 inch.--Translator's Note.)

The two ends of the ellipsoid have the same form, so much so that it is
only thanks to an individual peculiarity, independent of the shape, that
we can tell the cephalic from the anal extremity. The cephalic pole is
flexible and yields to the pressure of my tweezers; the anal pole is
hard and unyielding. The wrapper is double, as in the cocoons of
the Sphex. (Cf. "The Hunting Wasps": chapters 4 to 10 et
passim.--Translator's Note.) The outer envelope, consisting of pure
silk, is thin, flexible and offers little resistance. It is closely
superimposed upon the inner envelope and is easily separated from it
everywhere, except at the anal end, where it adheres to the second
envelope. The adhesion of the two wrappers at one end and the
non-adhesion at the other are the cause of the differences which the
tweezers reveal when pinching the two ends of the cocoon.

The inner envelope is firm, elastic, rigid and, to a certain point,
brittle. I do not hesitate to look upon it as consisting of a silken
tissue which the larva, towards the end