Just like humans can take a bus, a train or an airplane, freshwater snails can take a beetle, an elephant or a duck

Author: Julián Monge Nájera, Ecologist and Photographer 

Documented cases of freshwater snails using unexpected means of transportation explain how these slow animals reach ponds, lakes and rivers separated by land or ocean, with ranges that go from Canada to Brazil and the Caribbean islands.

Tiny snails of the species Fonscochlea accepta occur in hundreds of natural water springs in the desert of central Australia: do they reach these isolated springs through underground water connections between the springs? This is more difficult than it may sound, because the underground water is pressurized; maybe animals carry them from spring to spring, but nobody knows for sure¹.

There are, however, documented cases of freshwater snails that are transported by other animals over long distances.

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Adult snails, and their eggs, have been found attached to predatory freshwater beetles like Dytiscus marginalis, Acilius sp. and Melodema coriaceum. The snails associated with these beetles are species of Ancylidae², a family of hard-shelled gastropods that feed on underwater microvegetation and can breathe in both water and air, thanks to having pseudo-branchiae and lungs.

Freshwater snails have also been found in the bobolink (Dolichonyx oryzivorus), a long-lived bird that feeds on grains and insects and migrates between South and North America².

In the 1980s, Canadian zoologist David A. Boag made experiments with young pond snails of the species Lymnaea stagnalis, Stagnicola elodes, and Helisoma trivolvis, and found Helisoma trivolvis could potentially survive 10 km trips along the migration routes of ducks between Central America, the Caribbean and North America³.

His experiments, though, only tested snails attached to isolated feathers, and most died from dehydration; in real life, the snails would travel protected inside a feather coat or adhered to mud on the duck´s body, and probably could survive much longer periods and distances. 

Live snails and their eggs have also been found adhering to hair and mud in mammals, even in African elephants that travel hundreds of kilometers per day from one watering hole to the next ⁴, but probably the best friend of freshwater snails is our species: we carry them everywhere in our muddy boots and tools, and on a much larger scale, we have taken them to much of the world through the huge and growing aquarium trade⁵. 

*Edited by Katherine Bonilla y Carolina Seas.

Originally published  in Blog Biología Tropical: 24 September 2020

REFERENCES

¹ Worthington, W. J., et al. (2008). The influence of multiple dispersal mechanisms and landscape structure on population clustering and connectivity in fragmented artesian spring snail populations. Molecular Ecology, 17(16), 3733-3751. DOI: 10.1111/j.1365-294X.2008.03861.x
² Rees, W. J. (1965). The aerial dispersal of Mollusca. Proceedings of the Malacological Society of London, 36(5), 269-282.
³ Boag, D. A. (1986). Dispersal in pond snails: potential role of waterfowl. Canadian Journal of Zoology, 64(4), 904-909. DOI: 10.1139/z86-136 
⁴ Van Leeuwen, C. H. et al. (2013). How did this snail get here? Several dispersal vectors inferred for an aquatic invasive species. Freshwater Biology, 58(1), 88-99.
⁵ Yanai, Z., et al. (2017). The pet and horticultural trades as introduction and dispersal agents of non-indigenous freshwater mollusks. Management of Biological Invasions, 8(4), 523-532.