AND THEIR TRANSFORMATIONS. 23 
skin, the caterpillar prepares to undergo its change to the chrysalis state, and spins a little hillock of silk, which 
it seizes firmly with the hooks of its anal feet. It has still, however, to construct a silken girth across the middle 
of its body, which it effects ina manner the most simple and least liable to accidents of the three modes adopted for 
this purpose by the different kinds of caterpillars which fasten themselves by girths. The swallow-tail butterfly 
presents us with one of these modes, in which, owing to the comparatively slight flexibility of the body, the 
caterpillar is forced to hold the skein of silk open by means of its fore legs. The species of hair-streaked butterflies 
(Thecla) offer another mode, as will be detailed in our observations on that genus ; but the caterpillars of this 
genus have a very flexible body, so that they are able to throw back the head until it extends to the back of the 
fifth segment of the body, its fore legs being elevated in the air, it then applies the spinneret of its lower lip to 
the surface on which it is stationed, close to one of the first pair of fleshy prolegs, and has only to carry its head 
over the body to the opposite side to fix the other end of the thread. It then causes its head to return by the 
same route, emitting a second silken thread in like manner, one end of which it fastens at the spot at which the 
first was terminated, and the other end where the first was commenced. By repeating this mancuvre a certain 
number of times, the skein of silk becomes sufficiently strong to bear the insect, and Reaumur states that it is 
composed of about fifty threads, as he had observed a caterpillar spin thirty-eight, and about a dozen had been 
already spun when he commenced the observation. The number of these threads being completed, it only 
remains for the caterpillar to disengage its head from beneath the skein; a thing which might appear difficult, 
but which is easily effected by the caterpillar: to effect this it brings the head close to the surface on one side, 
where the threads are all fastened together, where in fact there is less liability to separate them from each other, 
which would be the case were the head to be withdrawn whilst it lies upon the middle of the back of the 
caterpillar, when the threads are of course loosest. It is then carefully withdrawn. The skein might be supposed 
to be too loose for the chrysalis, being spun over the body when that is doubled ; but the future movements both 
of the caterpillar and chrysalis require that the skin should not be too tight, but should allow a little play in all 
directions ; moreover the body, of course with the head turned back, as in the operation of spinning the skein, 
was stretched out, so that its natural diameter was considerably reduced. Having thus completed its skein, it 
reposes quietly at full length, or rather its body contracts in length and becomes thicker, and at length the skin of 
the fore part of the back bursts and the head of the chrysalis appears ; by continued writhing of the body the 
slit is enlarged and the skin pushed backwards beneath the skein of silk and thrown off at the tail, in the manner 
described under P. Rape. 
This butterfly appears in the perfect state about the middle of May, or earlier if the weather be favourable 
according to Stephens. It deposits its eggs at the end of the month, the caterpillars from which are soon hatched 
and feed together until the end of June, when they change to chrysalides, which period lasts from seven to about 
sixteen days (according to the heat of the weather). The perfect butterfly appearing therefore in July, and 
depositing eggs which produce caterpillars which become full-fed so as to undergo their change to chrysalis 
in the autumn, in which state they remain till the following May. It is very common throughout Europe, and 
is also found in Egypt, Barbary, Siberia, Nepaul, and even Japan. The individuals from the two latter localities 
are, however, doubtfully regarded by Boisduyal as distinct. 
