[Illustration:  Fig. 12.]

The expanded wings, Fig. 12, male, measure about two inches, are white above, with the base dusky.  Both sexes have the apex black and a black spot a little beyond the middle, and the female, Fig. 13, has another spot below this.  The under side of the fore wings is white, yellowish toward the apex, and with two black spots in both sexes corresponding to those on the upper side of the female.  A little beyond the middle of the costa, on the hind wings, is an irregular black spot on the upper surface, while the under surface is pale lemon yellow without marks, but sprinkled more or less with dark atoms.  The body is black above and white beneath.

[Illustration:  Fig. 13.]

The caterpillars of this insect feed on the leaves of cabbage, cauliflower, turnip, mignonette, and some other plants.

The female lays her eggs on the under side of the leaves of the food plants, generally, but sometimes on the upper sides or even on the leaf stalks.  They are sugar loaf shaped, flattened at the base, and with the apex cut off square at the top, pale lemon yellow in color, about one twenty-fifth of an inch long and one fourth as wide, and have twelve longitudinal ribs with fine cross lines between them.

The eggs hatch in about a week, and the young caterpillars, which are very pale yellow, first eat the shells from which they have escaped, and then spin a carpet of silk, upon which they remain except when feeding.  They now eat small round holes through the leaves, but as they grow older change to a greenish color, with a pale yellow line along the back, and a row of small yellow spots along the sides, and eat their way down into the head of the cabbage.

[Illustration:  Fig. 14.]

Having reached its full growth, the caterpillar, Fig. 14, a, which is about an inch in length, wanders off to some sheltered place, as under a board, fence rail, or even under the edge of clapboards on the side of a building, where it spins a button of silk, in which to secure its hind legs, then the loop of silk to support the forward part of the body.

It now casts its skin, changing to a chrysalis, Fig. 14, b, about three-fourths of an inch in length, quite rough and uneven, with projecting ridges and angular points on the back, and the head is prolonged into a tapering horn.  In color they are very variable, some are pale green, others are flesh colored or pale ashy gray, and sprinkled with numerous black dots.  The winter is passed in the chrysalis stage.

After the caterpillar changes to a chrysalis, their minute parasites frequently bore through the outside and deposit their eggs within.  These hatch before the time for the butterflies to emerge, and feeding on the contents, destroy the life of the chrysalis.

Birds and spiders are of great service in destroying these insects.

The pupae should be collected and burned if the abdomen is flexible; but if the joints of the abdomen are stiff and cannot be easily moved, they should be left, as they contain parasites.