Nematocampa resistaria

It is a pity that I have not managed to obtain a successful photograph of the adult of this species, also formerly known as Nematocampa limbata or N. filamentaria, for its cream and brown pattern is rather unusual. However, its caterpillar, sometimes called the Horned Spanworm, is so remarkable as to deserve to be included in its own right. It has been recorded on many trees, shrubs and herbaceous plants, but on southern Vancouver Island I have always found it on Black Hawthorn Crataegus douglasii. It 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 process. 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.