How fast does a slug crawl? From time immemorial, that profound question has occupied man's mind, puzzling and frustrating the primitive hunter-gatherers and the cerebral Nobel prize winners alike. Despite millennia of research and rumination, only recently has the humanity attained the necessary technological and intellectual stage to successfully tackle this seemingly insolvable conundrum. Snail's Tales is now proud to announce that a partial solution to the problem has indeed been obtained and will hereby be presented.
Without further ado, here is a slug of the species Arion subfuscus traveling vertically on a beech trunk. The horizontal lines mark the positions of the front of the slug's head at the indicated times.
The slug covered 106 mm in 4 minutes*, which corresponds to a speed of 26.5 mm/min. I carried out similar measurements with 2 other slugs of the same species. The fastest one was moving at 36 mm/min, or 2.2 m/hour, or 52 m/day, or about 19 km/year.
I noticed that while coming down the tree, the slugs had a peculiar mode of locomotion: it looked as if they were rappelling down using their slime. I don't know if anything has already been published on that, but I will return to the subject in the future.
I suspect that on a horizontal surface, especially on one that is not as smooth as a beech trunk, slugs' speeds will be less. The crawling speed of a slug may also depend on air temperature and humidity, whether or not the slug is also grazing on the tree surface while crawling, its species and size and the slope as well as the microscopic characteristics of the surface. There may be other factors that influence crawling speed.
We are continuing our research in this field of cutting edge malacology. Updates will be posted here.
*I ignored the slight curvature in the slug's path.