THE GREEN-VEINED WHITE BUTTERFLY. (Pieris Napi.)
([Plate IV]. fig. 4.)
Is so called from the greenish tint that often borders the veins or nervures on the under side of the hind wing; but the name is not always an appropriate one, for a large proportion of the specimens met with have the veinings grey, and not at all green; but the fact is, that the ground colour varies greatly, from creamy white to full buff, or bright clear yellow; in the latter case it is, that the minute black scales which border the course of the nervures, covering over the yellow, produce a grey-green effect on the eye.
The size also is very variable. I have a specimen that expands two inches and two lines across, from tip to tip, and have seen another not larger than a small Copper butterfly—little more than one inch from tip
to tip. The intensity of the dark markings, on both the upper and under sides, is also subject to much variation.
But, under all these circumstances, the presence of dark cloudy veins on the under side—appearing, but less distinctly, on the upper side—will at once distinguish it from the last species, the only one with which it can possibly be confounded.
The male has only one round spot on the front wings; the female being marked as in the plate.
Both in woods and cultivated grounds we meet with this butterfly commonly enough, most abundantly in May and July, though it may be found from April to August.
The caterpillar feeds on the same tribe of plants as the two last, but is supposed to be especially attached to the Rape (Brassica Napus), whence its specific name. Its colour is green, with yellow spots round each spiracle, which is itself tinged with red.
Two varieties of this were formerly ranked as distinct species, under the name of P. Sabellicæ and P. Napæ.