The Grimness of Nature, Part 2

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When Jody sent me this video last week, I didn't even know what I was looking at and thought it was a two-headed snail (even though that made no sense . . . were the two heads wanting to go in conflicting directions? No.). But Jody reminded me that snail eyes are at the end of the tentacles, not on their head. I still had no idea what I was seeing. 

Leucochloridium infected amber snail (Jody's photo)

Jody told me I was watching the action of a parasitic worm, Leucochloridium, that was residing in the eyestalks of the snail. The worm dances in order to imitate caterpillar behavior. The worm wants to be eaten by birds, but the dancing eyestalks need to be seen by the birds, so the worm manipulates the snail's behavior and coerces it to climb as high as possible in daylight (the snails are nocturnal in order to avoid drying out in the sun). A bird will see this faux caterpillar and peck out the snail eyes in order to eat it. Inside the bird's guts, the worm reproduces, the bird defecates the worm eggs, the eggs are eaten by another snail, and the entire cycle repeats.

This isn't the end of the snail, however. The bird only eats the eyestalks, which regenerate and the snail lives on to see another day. It will again reproduce and create more little hosts for more little worms. 

Amber snail (Genus Succinea)

The only type of snail I see is the amber snail, an entire family (Family Succineidae) of many species of snails worldwide. All of ours here seem to be of the same species but nobody seems to know (or care) which species. Since Leucochloridium only preys on amber snails, I am in a perfect position to find an infected snail.

Below is a photo of what could be snail eggs. Or slug eggs. I find them under rotting wood where it is damp. They are like little jewels.

You can also find these infected snails and observe their behavior. Look on the vegetation, not down near the ground. Remember, the worm forces the snail to climb as high as it can. Good luck!

Wired: "The Parasitic Worm That Turns Snails Into Disco Zombies"

W. Wesołowska, T. Wesołowski: "Do Leucochloridium sporocysts manipulate the behaviour of their snail hosts?"

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