Under the Shell

By Erin Watson

Contrary to popular belief, snails don’t always eat humans.
This is part of a larger painting by Robert Huskisson, titled 'The 
Midsummer Night's Fairies' (1847) on display at Tate Museum in London. 

When I was growing up, one of my chores was to kill the snails in my mother’s garden. Every Sunday I would head out into the front yard armed with salt and wage war on the gastropods. Salting them individually isn’t particularly efficient, and I eventually switched to throwing them into the busy intersection by my house and letting passing cars do the dirty work. In hindsight, I’m lucky I didn’t get sick, many snails carry parasites and children who don’t wash their hands can become accidentally infected hosts.

Humans can become infected as
accidental hosts, but the parasite won't be able to
complete their life cycle. 

Hundreds of millions of people suffer from snail borne parasitic diseases. Some of these parasites, like the schistosome worms that live in blood vessels, are considered world health concerns. Others, like the parasites that cause “swimmer's itch”, are more likely to just be irritating. Each one of these parasites use a unique set of snail species as invertebrate hosts, which makes exploring snails and their parasites an important health interest. Though they are often ignored, snails are economically interesting. They can cause massive crop damage by eating field bare and can carry plant diseases from one field to another. Snails are eaten all over the world, and their mucus is found in several cosmetics, especially anti-aging lotions. For my PhD research in the UNMs biology department, I focus on Cornu aspersum, the brown garden snail. I think it’s extra interesting because it’s highly invasive, it has lots of parasites, and it’s found all over the world.  Invasive species, like the brown garden snail, affect the types and densities of parasites in a particular ecosystem. They can bring new parasites and diseases into an ecosystem or they can be new hosts for parasites already in the ecosystem. 

Snail Selfie! Here is a photo that I took of C. aspersum
from my lab at UNM.

How C. aspersum responds to parasites isn’t well understood, but it matters for us humans. Humans have immunological responses, like fevers when you have a cold or inflammation when you get cut; your immune system fights off parasites too. Though it doesn’t look like ours, invertebrates have immune systems as well. For example, even though mosquitoes transmit malaria to humans, they have their own immune response to the malarial parasites as well.  Understanding how snails respond to the parasites they carry give us insights into how to fight them. My research focuses on the immune responses of C. aspersum, starting with its blood. C. aspersum has pale blue blood due to high levels of the protein hemocyanin, and in its blood there are cells that fight off disease called hemocytes. We actually know very little about these cells, we don’t even know how long they live! Using classic cell staining and microscopy techniques, I am exploring how these cells respond to microscopic foreign invaders. Do they eat invaders through the process of phagocytosis? What proteins do they use as weapons against invaders? Do the hemocytes kill invading parasites or is it something else? 

Understanding the snail immune system is crucial to being able to farm them safely. Farmed snails can be used for food or cosmetics, and understanding their immune systems means healthier snails that won’t transmit diseases to the people eating them. We can also use this knowledge to prevent diseases from being transmitted from wild populations to humans. With a little love and research, these snails can make the world a happier, healthier place; even if they still destroy my mother’s garden. 

Erin Watson-Chappell is a PhD student in the UNM Biology Department where she studies the 
immune systems of snails. The consummate lazy person, parasites are just her style.