Q. Why would slugs risk trying to cross a road, as I have observed on my morning jogs? Many of them dry out and die.



A. Whatever shortage of food or mates may have driven them to it, their behavior was outside the normal; perhaps a copious rainfall produced a false sense of safety. And their minimal nervous system provides no mechanism for warning other slugs of danger. For many species of slugs and snails, paved roads do present an effective barrier to their travels, so much so that studies suggest that road building can lead to population fragmentation and decline.

One such study, involving the European species Arianta arbustorum, was published in 1990 in The Canadian Journal of Zoology. When marked snails were observed over a three-month season of activity, they tended to restrict themselves to belts of vegetation along a paved road, where food and moisture were presumably plentiful.

The two big impetuses for sluggish movement are food-seeking and the search for potential mates. Oregon forest snails, Allogona townsendiana, like other species, were observed to reserve these activities for periods when the ground was moist. They hibernated in cold, dry months and dealt with hot months by burying themselves in leaf litter. C. CLAIBORNE RAY question@nytimes.com