Re: how much water does an earthworm need to survive?

Hi Henry,

Hmm, you've asked an intriguing question. You're right, earthworms need to stay moist. They breathe through their skin, and respiratory exchange occurs much more readily across a moist surfance than a dry one. Rather than rely on the environment to provide just the right amount of water to keep the skin moist, earthworms actually secrete a thin mucus-like substance that oozes out over the skin and facilitates breathing.

However, an earthworm must strike a delicate balance between being wet enough to breathe, and being too wet. Earthworms can, in fact, drown. This is why you often see earthworms emerging from their burrows after it rains -- if their burrows fill with water, the worms come up to the surface seeking air. A question similar to yours has been asked and answered on another forum.

It's a bit more difficult to answer the precise question "How much water does an earthworm need?". I'd guess that if you took an average-sized worm (10-20 cm), it would take much less than 1 mL of water to moisten the skin enough that the worm can breathe. Much more than that (for example, if you submerged a worm in a small puddle of water), and the worm would drown.

I hope this answer helps. You might be able to find additional information if you do a Google search for something like "earthworm breathing". I used the following textbook as a resource to answer this question:

Brusca and Brusca, 2003. Invertebrates. Sinauer Associates, Inc. ISBN 0-87893 -097-3

Allison J. Gong
MAD Scientist