A reader asked us an interesting question recently about some red worms in his fish tank. Although his question is preceded by some background information, he is primarily concerned with how long red worms can live under water in a fish tank. Since red worms are earthworms, his basic question is this: how long can earthworms live under water? Indeed, since earthworms are very often referred to simply as “worms,” his question can be made more simple still: how long can worms live under water? We explore both this general question and the reader’s specific concern below.
You might wonder why red worms, which are also called red wrigglers (among several other names), are in our reader’s fish tank to begin with. If people are familiar with red worms at all, they know them primarily as the worms used in compost operations. However, red worms are versatile creatures that can be used for many things, like feeding one’s fish. In fact, lots of people breed red worms for the sole purpose of feeding them to their fish. The reader attempted to feed his goldfish red worms, but for whatever reason the fish didn’t want to eat them, so he now has some red worms living in his tank; hence his question about the length of time that red worms can survive under water. They have already been under water for 10 days – how long will they last?
The answer, as is so often the case, is it depends. In particular, it depends on the amount of oxygen in the water. Unlike many animals who need oxygen to survive, worms have no lungs. Rather, they “breath” with their skin. Worms need to stay moist because oxygen dissolves on their wet skin, sending the oxygen into the worms’ bloodstream. In general, there is not enough oxygen in water to sustain a worm, so a worm will eventually suffocate (i.e., drown) if they are left under water. However, this can take several weeks, and if enough oxygen is dissolved in the water in which a worm lives, the worm could theoretically live indefinitely.
We have just been using the word “worm” to mean earthworm, which is, as mentioned above, what red worms are. However, the definition of the word “worm” encompasses more than earthworms. As such, there are plenty of worms that can and must live under water. There are an enormous number of marine worm species. Polychaetes, for instance, are primarily marine worms, and there are over 10,000 species of polychaetes in the world, and this only scratches the surface of the total number of worm species that are aquatic.
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So, for a great number of worms, their entire existence is spent underwater. They can stay under water as long as they live. Other species of worms that are not aquatic, like red worms, can only survive under water for a limited amount of time, however. More specifically, they can survive as long as there is a supply of dissolved oxygen in the water that can make it into their bloodstream, but once this runs out, they drown like any other animal that needs oxygen to survive.