WHITE CABBAGE BUTTERFLIES. 
89 
On the 29th of July Mr. Ackworth wrote me, with a specimen 
accompanying, that the attack “ at the present time is doing us 
incalculable mischief among nearly all our green crops. ... We 
have spent a lot in hand-picking and yet they swarm, as I believe 
fresh broods are continually hatching. 
“ What I want more particularly to ask your opinion of, is the 
mass of yellow silky substance we are now finding, wherever the 
caterpillars are, and invariably one is stretched across these and half 
dead ; and in one instance there appeared to be small grubs or maggots 
hatching therefrom and feeding on the caterpillar. At first, when 
hand-picking, we smashed these, but we are now perplexed as to 
whether this is advisable.” 
The above is an excellent description of the early condition of a 
small, black, four-winged, parasitic fly (scientifically the Microgastsr 
glomeratus, Linn,), which is one great means of checking increase of 
Cabbage Butterflies. This parasite ichneumon fly lays its eggs in the 
butterfly caterpillar, within which the parasite maggots feed, until the 
caterpillar on which they are preying has reached its full growth, or 
more, as these caterpillars full of maggots may often be known by 
their large size. The maggots then come out, and each spins a small 
yellow case like a small silkworm cocoon, and the infested caterpillar 
dies just when otherwise it would have been turning to chrysalis. 
The little clusters of yellow cocoons may be seen in great numbers 
where there are many Cabbage caterpillars and should never be 
destroyed, as the flies from them will do good again with the next 
generation of caterpillars. The clusters or bunches of cocoons may 
be easily collected and thrown aside under boards or in sheds or any 
convenient shelter, without needing any further trouble. 
On July 29th Mr. Ackworth wrote that, “ thanks to the ichneumon 
fl y so many caterpillars were found dying, that from this, with a 
heavy recent shower, the field was then nearly clear of the pest” ; and 
he further added, “ we continued hand-picking the smaller plants, and 
I hope now we have got through the worst of it.” 
The help given by the heavy rain-shower is well worth notice. Sudden 
rain will sometimes so affect Cabbage caterpillars that they become 
mere lax skins, with cream-coloured fluid within, and it would be well 
worth trying, where water and means of applying it is at hand, 
whether thorough drenchings applied by engines would not have a 
similar effect. 
Waterings or “washings” of weak brine or soapsuds have been 
found useful, and in the case of the Large Cabbage Butterfly, which 
lays its eggs in patches under the leaves , as figured at 2, p. 87, it would 
be worth while to have these looked for and the bits pinched off and 
destroyed. 
