Among those which have recently been found most injurious 
to the poplar is a large and rather handsome, light yellow or pale 
green, very hairy caterpillar (Fig. 5), most easily known by five 
long pencil-like tufts of black hairs rising one l3ehind the other on 
the middle line of the back, the first on the fourth segment of the 
body and the fifth on the last. This caterpillar was particularly in- 
jurious to poplars and considerably so to willows in Chicago in 
. 1909. It has been noticed by us also in Peoria, Danville, and East 
St. Louis. It feeds on the leaves in midsummer and again in fall, 
there being two generations in a year. It sometimes completely 
Fig. 5. 
The Yellow Poplar-Caterpillar, Apatela populi, 
natural size. 
strips a tree, rendering it unsightly and putting it in poor condition 
to withstand unfavorable conditions or to resist the attacks of 
more destructive insects. 
The caterpillar when full grown is about an inch and a half long, 
the skin yellowish-green, and the long, soft, drooping hairs yellow. 
The pencil-like tufts referred to rise from the fourth, sixth, sev- 
enth, and eleventh segments, those on the seventh and eighth being 
the smallest. The head is shining black and there are black spots 
on the top of segments one and two. The young are almost white, 
and the black tufts of hairs are shorter, but still conspicuous. The 
caterpillar is of a sluggish habit, and when at rest it commonly lies 
curled up, with the ends of the body together. When full grown 
it spins a loose, pale yellow cocoon of silk interwoven with its 
own hairs. This is generally placed in a crevice of the bark, under 
the edge of a fence board, or in some similar sheltered place. The 
winter is passed in this chrysalis stage, from which a large, pale 
gray moth emerges the following May. 
The caterpillars are most easily destroyed when young, for they 
do not at first scatter from the branch upon which they were born. 
