Weird locomotion – ‘upside-down gliding’ by snails

This has nothing to do with my research but I find this next observation a really interesting natural history occurrence; Snails floating upside down on the water surface (Figs.1-2). I noticed this behaviour for the first time three years ago when I was doing fieldwork near Ottawa, I thought “cool” and “that’s weird” and “why do they do that?” at the same time but I had my thesis to focus on at the time so I didn’t put much more thought into it. I noticed it again this summer in Fredericton while on a walk with my dog and thought it is time to think about some more.

Fig. 1: upside-down gliding behaviour by a snail

If you do a quick google search of “snail swimming upside down” you get hundreds of thousands of hits asking whether the snails in their tanks are dead, I suspect that a portion probably have died but the other portion may be doing this behaviour. So now I know that this upside down swimming also happens in both natural (field) and home/lab (experimental) settings. During this google search I also found a paper that looked at the mechanism of this behaviour they termed “Upside-down Gliding” (Aono et al 2008 – A project worked up by a group of high school students). They focused on the mechanism of the behaviour but not why. They were very thorough; in a lab setting, they measured the speed of locomotion, whether the snails secrete mucous while they’re upside-down gliding and whether the cilia on their foot is beating. Apparently, a snail can go between 0.8-1.6mm/s while upside-down gliding (depending on time of day and temperature), they secrete mucous and the cilia on their foot beats to move them forward. I found these finding very interesting but they did not answer my question of why the snails do this behaviour.

Fig. 2: Close-up of upside-down gliding snail.

I can only speculate as to why: (1) maybe it depends on the oxygenation in the water, there’s not enough oxygen in the water so they glide at the surface; (2) maybe they’re feeding, gleaning particles off the surface of the water, (3) maybe it’s safer, fewer of their most dangerous predators at the surface, (4) maybe it has something to do with parasitism, (5) maybe they can move faster this way than if they were at the bottom, (6) maybe it’s a way of finding mates, (7) maybe they’re drunk (I found this last one on a google site and I very much doubt that’s happening).

I still don’t know the answer why snails glide upside-down… but it’s a lot of fun to watch them do it. Natural history observations in action! (I’ll try to post more of these kinds of natural history observations)

 

Reference

Aono, K., Fusada, A., Fusada, Y., Ishii, W., Kanaya, Y., Komuro, M., Matsui, K., Meguro, S., Miyamae, A., Miyamae, Y., Murata, A., Narita, S., Nozaka, H., Saito, W., Watanabe, A., Nashikata, K., Kanazawa, A., Fujito, Y., Yamagishi, M., Abe, T., Nagayama, M., Uchida, T., Gohara, K., Lukowiak, K. and Ito, E. 2008. Upside-down gliding of Lymnaea. Biological Bulletin 215: 272-279.