Nematocampa resistaria

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.