Combating homelessness with figs and pumpkin seeds

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Once in a while you come across a story that is just so weird that you need to find out more. This happened to me last week. During a meeting, Menno Schilthuizen told the story about the snail that lost his home. Apparently, there are 3 papers dealing with this phenomenon. All three are about sea snails that for some reason crawl out their home and leave it behind (you also have slugs, those never have carry a house). After some research it appears to happen more often than I expected, not only in water bound snails. So I decided to write a post about this phenomenon and a possible solution (if you have land snails).

Losing your home

Snails always carry a house with them. This protects them against all sorts of things, but mostly against predators (although this doesn’t always work, see this post). Leaving it behind is generally a bad idea and is usually prevented by their columellar muscle. Karen Koy of the University of Illinois noticed that some of the sea snails she collected (Nucella lamellose) left their home behind and went on a nice nude stroll. Unfortunately for the snail, he was not alone in the tank.

The first ‘‘naked’’ snail was rapidly consumed by crabs that were kept in the same tank, so all future specimens were maintained in an isolation chamber.”

In the absence of crabs, these naked snails were able to survive for several weeks. Also in another snail (Littorina littorea), naked individuals were noted. After scouring some forums, I found that there are many cases of naked snails. I personally find snails quite pretty, a naked snail however, looks a bit terrifying (see pictures below).

Shell-less_Snail_ennemis_angiostoma1Shell-less_Snail_ennemis_angiostoma2Might it be caused by parasitic nematodes?

Why would a snail leave its house behind? Frankly, it is unclear. There are some theories. Stress might cause them to weaken and the columellar muscle might simple be unable to hold on to the shell. When the snail moves the shell stays behind. Another one is about parasites. Parasites are not the favorite animals of most people (including me). They can have very complicated life-cycles. A life-cycle is not much more than the steps taken to get from one generation to the next. We humans have a relatively easy life-cycle, parasites can have very complex ones. For example, a nematode (a sort worm) which has 1 stage of its life-cycle in the snail, but needs to get into a mouse to mature (see figure below). From that mouse they need to get back to snails again. So for the nematode to reproduce, it needs to get from the snail to the mouse first, then get back to the snail. The mouse eats the snail, the snail eats mouse droppings (or comes into contact with them).

Life-cycleBut what does that have to do with naked snails? Well, many parasites manipulate their hosts in order to get from one stage to another. It is possible that the nematode manipulates the snail to leave its shell behind, this naked snail is much more likely to be eaten by a mouse. The nematode reaches its goal (the mouse), which is a shame for the snail. The nematode that is blamed for the naked snail in the picture is called Angiostoma aspersae. But as I said before, we don’t actually know exactly what is going on. If we want to know for sure, some scientist needs to get his/her hands on snails that show this behavior and examine them.

So what about saving them with figs and pumpkin seeds?

While reading experiences of people that have seen this phenomenon before, I read that feeding your snails figs (Smyrna figs or Calimyrna figs) and pumpkin seeds might help. Just grind them up and feed them to the snails! It is possible that these seeds contain some compound that the nematodes can’t stand. At least in one case this seemed to help. However, as always, scientific study is needed to confirm the effect of figs and pumpkin seeds against nematodes. If you encounter snails losing their shells (so no slugs!), try feeding them figs and pumpkin seeds. More importantly, don’t forget to go to the nearest scientist and make him/her examine them under the microscope! Otherwise we will never learn the truth behind the naked snail.

References

Koy, K. 2007. Shell-less Nucella lamellose (Gmelin) from the rocky intertidal zone of San Juan Island, Washington. Journal of Shellfish Research, 26(1):267-269. DOI: http://dx.doi.org/10.2983/0730-8000(2007)26[267:SNLGFT]2.0.CO;2

Read, K. H. 1965. Littorina littorea without shell. Proceedings of the Malacological Society, London 36:307.

Read, K. H. 1966. Littorina littorea without shell: a further note. Proceedings of the Malacological Society, London 37:127.

PetSnails Forum, http://petsnails.proboards.com/thread/8863/snail-come-free

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About author

Chris Jacobs (Chris Jacobs)

Evolutionary biologist, eco-evo-devo | seek to increase the understanding of science | PostDoc @ Max Planck Institute for Chemical Ecology.

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