600 
The Diamond-back Moth. 
the head and thorax grey or ochreous grey, antennae white, with 
some brown or fuscous rings. 
The moths lay their eggs for the most part on the underside of 
the leafage of their food plants, and we see plainly that this is the 
usual ravaging ground of the caterpillars ; still, they may be present 
sometimes on other parts of the plants. 
The caterpillars, when full grown, are about half an inch long, 
and peculiar in shape, as they taper slightly towards each ex- 
tremity. This is a marked charactei'istic. The colour is usually a 
delicate green or apple green, but this is variable ; in younger state 
the larva is often yellowish or greyish, with black head. 
When near full growth the head is usually grey or yellowish, 
marked with small black dots, and the next ring is remarkable for 
the absence of the two dark patches often found in small caterpillars 
of allied kinds, and instead has a number of very minute black 
specks. The rest of the segments have a few black dots, each bear- 
ing a bristle, but these cannot be made out without the help of a 
magnifying glass. Each of the first three segments bears a pair of 
claw feet, and there are also four pairs of sucker feet beneath the 
body, and another pair (which are very noticeable from being set 
out somewhat obliquely) at the end of the tail extremity. When 
alarmed, the caterpillar lets itself down by a thread, and swings in 
the air till it thinks fit to return by the thread to its previous locality. 
How long the caterpillar feeds I do not find noted. The nearest 
approach to time I find is the observation of Dr. Taschenberg 
regarding caterpillars from eggs laid in May (or found feeding about 
the beginning of June) spinning their cocoons about the beginning 
of July. The cocoons are formed on the under surface of the leaf- 
age of the food-plants, or on stems, or amongst seeds, etc. — in fact, 
in any convenient place on or near the food-plant, and vary some- 
what in appearance ; sometimes they are a mere open netAvork of 
white threads, sometimes thicker, and of a somewhat boat-shaped 
form, in the former case the colouring of the chrysalis can be dis- 
tinctly seen through the network. The characteristic colouring 
when nearly mature is whitish with some black streaks. This was 
very noticeable in some cocoons sent me by Mr. Moss of Peering, 
Kelvedon, Essex, from which diamond-back moths very shortly 
came out. In the early part of their formation the chrysalids may 
be green or brownish ; there appears to be a good deal of variety 
in this matter, so far as I can judge from the many specimens which 
have passed througli my hands this year. 
The time spent in chrysalis state is also variable. Professor 
Westwood gives it as from 10 to 18 days, John Curtis as about 11 I 
days, and Dr. Taschenberg as about three weeks. The first two ' 
observations were from specimens presumably under shelter, and 
the difi'ei enco points to the efTect wliich weather favourable to the 
development of the insect may have in increasing the prevalence i 
of this scourge. The second generation begins its ravages about 
August, and the chrysalids from the last brood of the year remain i 
in chrysalis state thiough the winter. 
