Earthworms have some regenerative abilities. But can worms regenerate completely after being cut? Can they cut themselves as a defence mechanism?
Since I was young, people told me that after cutting a few segments of an earthworm, each segment would grow into a new earthworm.
Obviously, this is wrong and a bit of an urban myth.
Earthworms are certainly not like how a starfish can grow back its tentacle or a gecko can grow back its tail after they’re cut off.
Do worms live if you cut them in half?
It’s true that earthworms have certain self-healing and regenerative capabilities, but there are also some limitations.
If you chop the earthworm into multiple pieces, then there is almost certainly no way it will survive, let alone have it grow back and regenerate.
So, can an earthworm really regenerate after being cut or cut in half? Not necessarily. Earthworms bleed too after being cut.
Strictly speaking, as most of the important organs of earthworms, such as the annulus, are close to the head, the regenerative ability of the front two-thirds of the worm is much stronger than that of the rear part.
For instance, if you cut an earthworm exactly in half, it is more likely that the part near the head can be grown back into a complete earthworm, while the rear part would die. (2)
When regenerating, with a serious injury, the earthworm needs a lot of energy to grow these organs back, and there is a high probability that the tail would die without being able to replenish this energy.
It’s not just the location of the worms cut either, the probability of recovery also depends on the age, species and health of the earthworm (1).
Does an earthworm cut itself ? It’s a way of self-defense.
Earthworms are different from geckos. Generally, artificially bred earthworms do not actively cut themselves to escape.
However, it is not uncommon for many wild species to self-cut to protect themselves. This phenomenon is called natural amputation or autotomy.
Specifically, when earthworms are in danger, they cut off a small part of the tail from the body.
The broken tail would twist and struggle until there is no more energy, and there would be enough time for the front part to escape.
But, there are even studies to show that earthworms do this to get rid of pathogens built up in certain areas of their body. Smart! (more on this later)
Among the earthworms that cut themselves which are commonly used for vermicomposting are the worms Eisenia Andrei (a close relative of the Tiger worm or Brandling worm, the Eisenia fetida) and the Aporrectodea caliginosa (The Grey Worm).
These worms are commonly found in Europe, mostly in the UK.
Even the Eisenia Fetida (you may know these as “red wigglers” – ring any bells?) have also been known to cut themselves in case they feel it’s necessary, but it’s much more rare in this species.
In universities in Taiwan and in the United Kingdom, some people have held the earthworms in their hands for too long, and it caused the earthworms to panic and cut themselves.
Perhaps even worms get scared of something so far from their normal environment, even though there is no imminent danger? It’s fascinating either way.
On the other hand as we mentioned earlier, earthworms cut themselves out of a response of the immune system.
Earthworms sometimes consume and accumulate pathogens and toxic substances, which they then store in the tail, such as heavy metals.
The purpose of cutting the tail is also to push these substances out of the body. A very clever survival mechanism.
So now we know earthworms can cut themselves and regenerate but another question this brings up is do worms have bones? ←- Find out in our article