The next time you get shampoo in your eyes and you’re writhing in pain in the shower, I want you to think about slugs. That’s right, I’m talking about those shell-less snails sliding about in your garden and on your trash cans, leaving slime trails across your patio. Why? Because researchers are designing a test to be used in slugs that would predict the eye-irritating potential of chemical substances.

Arion vulgaris or lusitanicus*

Terrestrial slugs are molluscs that lack a hard, external shell. They are only found in moist environments since their bodies are prone to dessication (drying out). This is best illustrated on mornings when I discover, littered across my concrete patio, the shriveled-up, turd-like carcasses of those slugs not fortunate enough to find wet refuge. In order to prevent their bodies from drying up, slugs constantly produce a protective layer of mucus to keep their bodies moist.

Dried up slug on my patio. Looks sort of like a turd. Some people see a duck’s head.

Of course, many of you might be more familiar with their propensity for creating mucus when salt is poured on a slug (which I do not condone). When a slug comes into contact with salt, it will secrete more mucus to maintain its protective barrier. Cover it with enough salt, however, and the slug will eventually dehydrate and die.

Now, researchers are trying to exploit the slug’s mucus-making abilities, but in less sadistic terms. They reasoned that the amount of mucus a slug produces when exposed to a chemical might predict how irritating that chemical would be to the human eye. To help conceptualize, just imagine someone blowing salt into your unsuspecting eyes–and if you’re wondering, yes, a “friend” of mine has done this to me**. To test their hypothesis they designed a slug mucosal irritation (SMI) assay, in which the researchers measured how much mucus the Portuguese land slug (Arion lusitanicus) produced in response to five different shampoos. They then compared these results with how irritating each shampoos was to the human eye using self-reported surveys and ophthalmologic evaluations. They report that, on average, shampoos that induced more slug mucus production also that caused more eye discomfort, indicating that the SMI assay can predict the eye irritation potential of shampoos. 

So, the question becomes whether or not the SMI assay will prove to be general and reliable enough to predict how irritating other chemicals will be to the human eye. One factor to consider is the natural variation among people in their ability to tolerate pain or discomfort. Another consideration is that some people might be sensitive to a particular chemical while others are not. That said, the group has also reported similar results for a similar SMI assay in its ability to predict the irritation potential of chemicals to human nasal membranes. In the end, the SMI assay may provide a cheaper and, for those of us who are squeamish, more palatable alternative to animal testing.

*Upon further reading, it’s unclear whether these images are of actual Arion lusitanicus. There seems to be a bit of misidentification between lusitanicus and vulgaris (Spanish slug).

** UPDATE (9/12/12) The perp has informed me that it was pepper, NOT salt, that was blown into my eyes.


Lenoir J, Claerhout I, Kestelyn P, Klomp A, Remon JP, Adriaens E. The slug mucosal irritation (SMI) assay: development of a screening tool for the evaluation of ocular discomfort caused by shampoos. Toxicol In Vitro. 2011 Dec;25(8):1919-25. Epub 2011 Jun 28. PubMed PMID: 21741469.

Related Reading:

Salt-maze kills the stupid slugs, rewards the clever

Are slugs under threat from a foreign ‘super breed’? (

Slug alert! Invasion of the gastropods (

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