472 
LEPIDOPTERA. 
becomes a chrysalis within the same shell, and in due time 
comes out a Platygaster fly, like its parent. This last trans- 
formation Mr. Herrick found to take place towards the end 
of June, from eggs laid in November of the year before ; and 
he thinks that the flies continue alive through the summer 
till the appearance of the canker-worm moths in the autumn 
affords them the opportunity of laying their eggs for another 
brood. As these little parasites prevent the hatching of 
the eggs wherein they are bred, and as they seem to be 
very abundant, they must be of great use in preventing 
the increase of the canker-worm. Without doubt such wise- 
ly appointed means as these were once enough to keep 
within due bounds these noxious insects ; but, since our 
forests, their natural food, and our birds, their greatest en- 
emies, have disappeared before the woodman’s axe and the 
sportsman’s gun, we are left to our own ingenuity, persever- 
ance, and united efforts, to contrive and carry into effect 
other means for checking; their ravages. 
Between the years 1841 and 1847, canker-worms almost 
entirely disappeared in the vicinity of Boston. At the latter 
date, there was a visible increase of them here, and their 
numbers have rapidly augmented every subsequent year. 
In a few years more, unless checked by natural or artificial 
means, they will probably prove as destructive as at any 
former time. The writer of this work has given repeated 
warning of these facts in the public prints, and has pointed 
out the remedies to be applied.* 
Apple, elm, and lime trees are sometimes injured a good 
deal by another kind of span-worm, larger than the canker- 
worm, and very different from it in appearance. It is of 
a bright yellow color, with ten crinkled black lines along 
the top of the back ; the head is rust-colored ; and the belly 
is paler than the rest of the body. When fully grown, it 
* See Prairie Farmer, VoL VIII. p. 172, for June, 1848. Massachusetts Plough- 
man, for June 24, 1848, Nov. 23, 1850, and May 17, 1851. Boston Cultivator, Nov. 
24, 1849. New England Farmer, Vol. II. p. 252, for August, 1850. 
