The surprising “bat snail” of Costa Rica

Author: Julián Monge Nájera, Ecologist and Photographer 

The cloud forest of Costa Rica is home to an extraordinary snail, with a behavior sometimes reminiscent of bats, sometimes of domestic cats. Its survival seems likely thanks to the hydroelectric production program of Costa Rica, one of the world’s most advanced countries in carbon neutrality.

Snails do not have dry skin to protect them from dehydration, and they need abundant water to produce the jelly-like substance on which they glide. They do everything to conserve humidity: their shells are usually light-colored and therefore reflect more heat; in addition, shells prevent the passage of water; snails prefer to be active at night or when the humidity is high after rain, and if necessary, they seal their shell, either with a calcareous lid (operculum) or with a temporary membrane (epiphragm). Their relatives, slugs, can even produce a mucous cocoon that they reinforce with moss and dirt.

The snail Tikoconus costarricanus has an additional technique to conserve valuable moisture. Costa Rican biologist Zaidett Barrientos studied it in the Río Macho Forest Reserve (maintained as aquifer security by the Costa Rican Electricity Institute) and observed something that no one had seen: the snail was hanging like a bat¹. 

After years of work, she was able to understand what was happening: when the humidity drops at a certain time of day, the snail begins to contract, covers its tentacles in “raises” the front of its foot from the ground (in this case, the «ground» is the lower part of the leaf to which it is attached). Barely hanging from the back of the foot, the snails wraps itself in its mantle as a person would with a blanket on a cold night. Then, it enters a state of inactivity in which only its breath is noticed, and it remains immobile until humidity increases, generally a few hours later¹.

To become active again, it follows the opposite sequence, I suppose because snails do not tend to complicate themselves unnecessarily: after all, they have always been seen by humans as an example of patience and tranquility.

If you want to see this incredible behavior, the article includes several  videos! https://revistas.uned.ac.cr/index.php/cuadernos/article/view/2802

From the point of view of these snails, their enemies can be huge, small like themselves, or invisible. We know almost nothing about the enemies of Tikoconus costarricanus, but they probably include large species, like birds and lizards, which eat them; small ones, such as parasitoid flies and planarians, which could also eat them; and invisible enemies, like flukes, nematodes, and parasitic protozoa, which could make them sick. All this remains to be studied.

How sad would it would be to see an enemy approach you and not be able to escape quickly! And this should be the case for snails, but not for Tikoconus costarricanus, this species can disappear at spectacular speed!

As Barrientos discovered, in the event of danger, the snail contorts violently, detaching itself from the leaf and instantly falling to the forest floor, where it is hidden somewhere in the dense litter where it is almost impossible to find it¹.

And why did I say that it reminds us of cats, too?

Because Tikoconus costarricanus cleans itself with its tongue, just like cats do. This surely protects it from fungi and bacteria, just as showers protects us from many skin pathogens1. Maybe other snails do it too, but, until the present, no one cared to study and publish it, so we must thank this Costa Rican biologist for reporting this grooming behavior. How many more surprising secrets does this little tropical mollusk keep?

*Edited by Katherine Bonilla y Carolina Seas.

Originally published  in Blog Biología Tropical: 20 august 2020

REFERENCES

¹ Barrientos, Z. (2020). A new aestivation strategy for land molluscs: hanging upside down like bats. UNED Research Journal, 12(1), e2802-e2802.