The remarkable caterpillar, sometimes called
the Horned Spanworm, has two processes on its back, which are normally curled
up, but occasionally the caterpillar periodically inflates them and wriggles
them, when each is seen to be a bifurcated organ. The caterpillar spends much
of its time in a doubled-up position, and it sometimes hangs from the edge of
a leaf by its prolegs with its body twisted in an unnatural fashion, the "horns"
sticking out at rakish angles. It is difficult to recognize as being a caterpillar
at all. It pupates in a spun-up leaf, and the moth emerges two or three weeks
later. It has been recorded on many trees, shrubs and herbaceous plants, but
on southern Vancouver Island I have found it on Black Hawthorn Crataegus
douglasii and on the dogwood Cornus stolonifera.
The cream and brown pattern on the wings of the adult moth is almost as remarkable as the caterpillar – it almost looks unreal. In early literature the moth can be found under the names Nematocampa filamentaria or N. limbata.