Huddling and tail-dipping: two previously unknown behaviours of the slug Megapallifera mutabilis (Philomycidae)

We report the behaviours of the North American philomycid slug Megapallifera mutabilis (Hubricht, 1951) in the wild and in the laboratory. In their forest habitat during suitable weather the slugs climbed trees to feed on the algae coating the bark and took refuge in water-filled tree holes. Inside the holes two or more resting slugs were often in physical contact with each other (huddling). Slugs were also observed dipping their tails into water. Our measurements indicated that slugs foraging on tree trunks tended to lose water and tail-dipping helped dehydrated slugs absorb water. Huddling has been previously reported for other slug species, but the exact functions of the behaviour remain unknown.