23 
They are capable, however, of fasting for a considerable time withr 
out injury, and they may even survive the destruction of the leaves 
by late frosts. They scatter for pupation late in May or early in 
June, spinning cocoons which they fasten among clusters of 
leaves or exposed on fences and in other similar situations. There 
is but a single generation in a year. The parent moths (Fig. 
21 ) measure about an inch and a quarter across the expanded 
wings. The general color is brownish-yellow and the fore wings 
are marked by two straight dark brown lines which cross them 
obliquely, parallel with each other and' the hinder edge. 
Trees may be protected by spraying with arsenical poisons 
shortly after the young caterpillars begin to appear, or by clipping 
off in winter the twigs bearing the conspicuous belts of eggs and de- 
stroying these by burning. Even overwhelming hordes may be ar- 
rested by surrounding the tree trunk with a band of cotton batting 
about four inches wide, tied around the middle with a string, the 
upper part being then turned downward over the string. Or, the 
trunk may be surrounded with a band of printers' ink applied as 
described in the article concerning the common canker-worm 
(p. 488). 
The Common Canker-worm, or Spring Canker-worm 
{Palcacrita vcrnata Peck) 
The common canker-worm is best known as a pest of the apple 
orchard, but it is sometimes even more destructive to elms (Fig. 22) 
than to apple-trees. It feeds also on cherry, at first eating small 
holes thru the leaves, but when larger devouring the whole leaf ex- 
cept the midrib and some of the coarser veins. Modern methods 
of orchard management require a regular and frequent spraying 
with arsenical poisons as a protection of fruit against the codling- 
moth, and this has the incidental effect — often unnoticed by the 
orchardist — of speedily killing oft' any colony of canker-worms 
which may have chanced to make a start in the orchard. Hence 
it is only neglected orchards, or those not in bearing either because 
too young or by reason of a crop failure for the year, which are 
liable to serious canker-worm injury. 
With the elm, however, the case is different. The canker-worm 
lives on this tree as willingly and successfully as on the apple. Elms 
are rarely sprayed in Illinois, and if the canker-worm once comes 
to infest them there is no natural end to the injury except the death 
of the tree, unless, indeed, the parasites of the insect and other 
natural checks on its increase may happily suppress it before that 
event. 
