“Wait a minute, what was that?” We retraced our steps, astonished. A pale tussock moth larva, inching its way along the parapet of Prebends bridge, had chosen the most precarious route possible to wander in search of somewhere to pupate. Gusting wind, sending withered leaves tumbling across the bridge, threatened to blow it into the river, 30 feet below.
My wife, more dextrous than I, coaxed the caterpillar into the collecting tube I always carry in my pocket. Immediately it curled into a defensive ball covered in rosettes of long, neon green whiskers, with a mane of bristles, four dense tufts like miniature shaving brushes on its back, and a menacing spike of rose-pink hairs at the tail. Everything about it warned “don’t touch me”.
It would present a challenge for most insectivorous birds, although cuckoos, with a gizzard that can cope with irritating hairs, sometimes eat them. Those deterrents inflict discomfort on tender human flesh too: finely barbed and filled with irritating fluid, they can cause dermatitis. Calliteara pudibunda was once a notorious pest of hop fields, which might explain the naturalist Gilbert White’s journal entry for 8 October 1781, noting that “several women and children have eruptions on their hands … after they have been employed in hop-picking”. More recently, families from London’s East End, travelling to Kent for traditional hop-picking work every autumn, would have been painfully familiar with these caterpillars, which they knew as “hop dogs”.
Pale tussock larvae are not picky about food plants and defoliate at least a dozen broadleaved tree species, including beech, hawthorn, sycamore and lime, all well represented along this riverbank. But, out of curiosity, I offered our captive some young shoots from the hop vine that twines through our garden fence. It had a nibble, but was fully fed and only interested in finding somewhere dry and secure among the leaf litter, where it will pupate inside a cocoon woven from recycled defensive bristles.
Hatched from an egg laid last June, this wanderer had escaped the attentions of birds, dodged drowning in the river and, provided it hasn’t already been parasitised by an ichneumon wasp, should survive winter, metamorphosing into a beautiful pale grey moth next spring.
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