90 Introduction to Insects (CH. 
of these wings. The under surface is white with a 
yellow tip and in the case of the female it has two 
black spots as on the upper surface (see Fig. 27d). The 
hind wing is white on the upper surface with a small black 
patch on the front edge. Underneath it is yellowish. 
The colours of butterflies and moths are due to the 
presence of numerous scales. 
After pairing the female proceeds to lay her eggs 
on a plant on which the caterpillars can feed. This 
butterfly has at least two broods every summer, that 
is to say the butterflies formed from the eggs laid in 
early summer give rise to caterpillars in the same 
summer. In favourable seasons three broods are formed. 
While in the caterpillar stage this insect is liable to 
attack from various enemies. Birds and wasps kill 
a considerable number. I have seen a single wasp kill 
five in half-an-hour. They are also attacked by a 
small ichneumon wasp which by means of a piercing 
organ lays its eggs in the body of the caterpillar. The 
young larvae hatching from these eggs feed on the 
inside of the caterpillar, thus causing its death, and 
eventually come out and form little yellow bodies or 
pupae (see Fig. 28). These bodies, which are falsely 
known as caterpillars’ eggs, should not be destroyed for 
they develop into wasps which lay eggs in other cater- 
pillars and prevent them from forming butterflies. 
In gardens the caterpillars can be prevented from 
eating cabbages by searching for and destroying the 
eggs in July and August. As the eggs are laid in 
groups this is not very difficult. Any caterpillars 
which hatch out may be destroyed at the same time. 
Most insects are similar to the cabbage butterfly in 
that they are derived from eggs. The old idea that 
