Insects of Shade Trees and Their Control. 37 
Appearance and seasonal history.—The cankerworm is the cater- 
pillar stage of a moth and comes from an egg laid by the female 
moth, which is always wingless. The eggs of the. fall moth are from 
50 to 150 in number, flowerpot shaped, and laid in regular rows and 
compact patches which are generally exposed in rings around twigs 
near the ends of branches. Those of the spring moth are egg shaped 
and are laid in irregular batches beneath bark scales. At the time 
the first leaves expand in the spring these eggs hatch into cater- 
pillars, which attain full growth in about four weeks (about June) 
and by a silken thread descend to the ground, there pupating a few 
inches below the surface. From these pupz the moths of the fall 
species usually emerge and lay eggs late in the fall or during 
warm days in winter. The males are winged, the females wingless. 
Soon after emerging 
the latter crawl up 
near-by trees and 
bushes to deposit. 
their eggs. 
Naturai control.— 
Cankerworms are 
subject to attack by 
a variety of insect 
enemies. Climbing 
ground beetles (fig. 
i. p.26)) <d evo ur 
many caterpillars ° 
bodily. Small para- Fic, 20.—Full grown caterpillars of the spring canker- 
5 worm. (Quaintance.) 
sitic wasps and flies 
lay their eggs in and on the caterpillars and in the eggs of the moth, 
and the ensuing grubs kill even greater numbers of them. Together 
these insects usually succeed in keeping the cankerworms in check, 
but if these fail, the cankerworms become seriously injurious. 
Artificial control.—It is impractical to attempt to combat these 
insects on trees in the forest, but shade trees can be protected as fol- 
lows: (1) Advantage may be taken of the winglessness of the female 
by keeping the tree banded (p. 17-20) with some sticky substance or- 
cotton bands to prevent her from ascending the trees to deposit her 
eggs. Such bands are most effective where applied toward the end of 
September and maintained in the spring until the end of May. These 
bands also prevent the worms that come from the undergrowth from 
ascending the trees. (2) Where banding has been neglected and 
evidence of heavy infestation is indicated by numerous perforations 
in the opening leaves, the foliage can be saved by prompt spraying 
with lead arsenate (p, 11). 
