Slug following a Closed Trail

Abstract

MY attention was drawn a few days ago to a brown slug, about 2½ inches long, which had made for itself a closed iridescent track on the concrete flooring of a conservatory. I could not find at what point it had got on to the curve, which ran at one end into a damp part of the concrete, but, in four hours from the time I first saw the slug, it had made three complete circuits and two-thirds of a fourth, always keeping the whole of its body on the trail. The latter, of a uniform breadth of 3/16 inch, varied considerably in curvature, but nowhere presented any very sharp corners, and measured, roughly, forty inches round. Though the rate of progression was sufficiently slow, the slug rested on the track for seven hours, after which, thinking it dead, I touched it and found it had not quite dried up. Indeed, without elongating its body, it began to move and laboriously shifted its position by about an inch. There it remained (the time being then 10 p.m.), waiting, perhaps, for the influence of a more humid atmosphere, for morning found it moist and healthy, breakfasting more than a yard from the near and damp end of the track, which it must have reached by completing the fourth circuit, as there was no trail other than the closed one alluded to. If slugs are in the habit of following old trails, it does not appear that the present specimen had any previous experience of a re-entrant path, but that it depended solely on ocular intelligence of the path in advance.