Are sea slugs harmful to people

March 10, 2001
From: Heidi Colonnese

I need to know if sea slugs are harmful to people if touched, my 8 year old came running up to me on the beach today excited, about finding a "sea snail", he was holding it in his hands, he washed them in the ocean, I also touched it while putting it into a bucket for viewing, i'd never seen such a thing and it was quite amazing. I also rinsed my hands, he touched it more than once and for a longer time than i did, the skin on my thumb did feel a little stinging, should that be the extent of the symptoms? we live in southern california, south orange county, the slug was dark colored either dark brown maybe a bit reddish. I'm so excited about finding your site i can't wait till he has a look at it, and learns about why we can't touch everything we find.
Thank you,
Heidi Colonnese

Colonnese, H., 2001 (Mar 10) Are sea slugs harmful to people. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Heidi,
I'm afraid without a bit more information I can't say whether the animal your son found was a sea slug or not. It is possibly a Sea Hare. Have a look at the Sea Hares Page and perhaps the page on Aplysia californica, which as its name suggests, is one of the Californian species of Sea Hare. Was your find a Sea Hare? If not, I would need some more information before I could hazard a guess.

If you find things washed up on the beach it is worth remembering that normally they live in water, so if you want an idea of their shape it's best to put them in a pool or a bucket of sea water so they have a chance to 'act naturally'. I wouldn't like to give advice on what is and what isn't dangerous to pick up on Californian shores. Seek advice from one of your local natural history museums. In general though, there aren't that many things which it is dangerous to touch. I guess it has to be balance between stimulating your son's natural curiosity and a mother's natural caution. My advice is to seek local knowledge on local dangers. I am sure they will be very few.

On your general question about whether sea slugs are dangerous. The only one I know which can cause a nasty sting is Glaucus atlanticus and its close relative Glaucus marginata. They live with, and feed on Physalia, the 'Portugese man-o-war', which can cause painful stings to swimmers. If you go to the Glaucus page your will see that Glaucus and Glaucilla store the nastiest stings from Physalia in their own bodies. But apart from these two species I think you will be fairly safe with sea slugs.
Best wishes,
Bill Rudman

Rudman, W.B., 2001 (Mar 10). Comment on Are sea slugs harmful to people by Heidi Colonnese. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


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