Yellow-necked caterpillars, walnut caterpillars, and
late first-generation mimosa webworm are still
causing damage in southern Illinois and in select locations
in central Illinois. Where defoliation is extremely severe
or where plant appearance is the most important aspect of
the landscape, treatments with any of the compounds listed
for caterpillar control in the 1997 Illinois Commercial
Landscape and Turf Pest Management Handbookshould
eliminate current infestations. Both yellow-necked and
walnut caterpillars feed as a group, so spot treatments or
removal of the caterpillars by pruning or physical
destruction are the most effective forms of management.
In addition to these common summer defoliators, we have
been seeing some damage on willows by spiny elm
caterpillars in the Chicago area. The larvae of this
caterpillar are black, about two inches long when fully
grown, and have white and burgundy spots along their backs.
They also have long spines around each segment. An
interesting fact about this defoliating caterpillar it
becomes the mourning cloak butterfly. For some people, this
poses a dilemma: What is more important--the appearance of
the plant or the beauty of the insect?