Show spiny elm caterpillar A spiny elm caterpillar about ivi inches long when full grown was found feeding on elm trees the body is black dotted with white W hite spots each body segment having a large orange spot on the top and several conspicuous thorn like projections it was identified as the spiny elm caterpillar aglais anti opa but it feeds upon the leaves of willow poplar elm and dogwood any stomach poison such as lead arsenate or calcium arsenate is effective fec tive small infestations may be handpicked hand picked the adult is the mourning cloak butterfly it is comparatively ively large with black velvet wings bordered with yellow |