Lepidoptera The Large White Butterfly – Pieris Brassica
We pass now from one of the rarest to one of the most abundant of British butterflies. Everybody has seen the ‘Large White,’ though we doubt whether everybody knows that this insect is not of the same species as the two other very common ‘Whites.’ The three-Large, Small, and Green-veined-are so much alike in general colour and markings, and so similar in their habits and in the selection of their food plants, that the non-entomological, not knowing that insects do not grow in their perfect state, may perhaps regard the larger and the smaller as older and younger members of the same species. But no-they are three distinct species, exhibiting to a careful observer many important marks by which each may be known from the other two.
On Plate I (fig. 3) will be seen a picture of the female Brassica, in which the following markings are depicted: On each fore wing-a blotch at the tip, a round spot near the centre, another round one nearer the inner margin, and a tapering spot on the inner margin with its point toward the base of the wing. On the hind wings there is only one spot, situated near the middle of the costal margin.
The male may be readily distinguished by the absence of the black markings on the fore wings, with the exception of those at the tips. He is also a trifle smaller than his mate.
This butterfly is double-brooded. The first brood appears in April and May, the second in July and August; and the former-the spring brood-which emerges from the chrysalides that have hybernated during the winter, have grey rather than black tips to the front wings.
The ova of Brassica may be found on the leaves of cabbages in every kitchen garden, also on the nasturtium, during May and July. They are pretty objects (see image), something like little bottles or sculptured vases standing on end, and are arranged either singly or in little groups.
As soon as the young larva are out-from ten to fifteen days after the eggs are deposited-having devoured their shells, they start feeding on the selfsame spot, and afterwards wander about, dealing out destruction as they go, till little remains of their food plant save the mere stumps and skeletons of the leaves.
The ground colour of the caterpillar is bluish green. It has a narrow yellow stripe down the middle of the back, and two similar but wider stripes along the sides; and the surface of the body is rendered somewhat rough by a number of small black warty projections, from each of which arises a short hair.
When fully grown, it creeps to some neighbouring wall or fence, up which it climbs till it reaches a sheltering ledge. Here it constructs its web and silken cord as already described, and then changes to a bluish-white chrysalis, dotted with black. The butterflies of the summer brood emerge shortly after, but the chrysalides of the next brood hybernate till the following spring.
It is remarkable that we are so plagued with ‘Whites’ seeing that they have so many enemies. Many of the insect-feeding birds commit fearful havoc among their larva, and often chase the perfect insects on the wing, but perhaps their greatest enemy is the ichneumon fly.
Look under the ledges of a wall of any kitchen garden, and you will see little clusters of oval bodies of a bright yellow colour. Most gardeners know that these are in some way or other connected with the caterpillars that do so much damage to their vegetables. They are often considered to be eggs laid by the larva, and are consequently killed out of pure revenge, or with a desire to save the crops from the future marauders.
No greater mistake could be made. These yellow bodies are the silken cocoons of the caterpillar’s own foes. They contain the pupa of the little flies whose larva have lived within the body of an unfortunate grub, and, having flourished to perfection at the expense of their host, left its almost empty and nearly lifeless carcase to die and drop to the ground just at the time when it ought to be working out its final changes. Often you may see the dying grub beside the cluster of cocoons just constructed by its deadly enemies. Should you wish to test the extent of the destructive work of these busy flies, go into your garden and collect a number of larva, and endeavour to rear them under cover. The probability is that only a small proportion will ever reach the final state, the others having been fatally ‘stung’ before you took them.