Re: Are worms and ants 'naatural enemies'

Dear Thomas,

This is a very interesting question. Biologists use the term natural enemy to refer to an organism which specializes in hunting a particular species of animal.

Occasionally, an animal will make it's way to a new area where it has no predators. Because there are no predators to keep population growth under control in this new environment, the population levels of the introduced animal become enormous. This can have a terrible effect on whatever the pest is eating in its new environment.

Traditionally, attempts were made to eliminate an introduced pest by spraying insecticide chemicals. Unfortunately, there are a lot of problems with the use of pesticides as the only means to control a pest. One problem is that most chemical insecticides are not specific to killing only the pest. Often they will kill many beneficial insects as well. This can make a bad situation even worse. Also, over time, the introduced pest populations can evolve resistence to the insecticides being used. Eventually, resistant pest populations can grow to great levels again.

To help overcome the problems of using only chemical controls, researches began using biological controls as well. In biological control, researchers begin with finding out where the pest naturally occurs. They then search for organisms that prey on the pest in it's natural habitat, a so-called natural ememy. Ideally they will find an organism that specializes on the pest. This prevents the new organism from harming other insects in the introduced ecosystem. For some examples of introduced pests and the natural enemies used to control them, see this site by the Association of Natural Bio-Control Producers.

Earthworms (and worms in general) are an understudied group of animals. Like many organisms that spend most of their lives out of sight, not a whole lot is known about their ecology. They seem to be of great benefit to ecologies both as aerators of the soil and as food for other members of the ecosystem. Many things eat worms, including toads, birds, and sometimes even ants. While earthworms (scientific name is Lumbricus terrestris) are a species introduced to the Americas from Europe, they are not usually considered pests here. Non-the-less we can still evaluate whether or not ants could serve as natural enemies of earthworms.

Do ants specialize in eating worms? It's tough to generalize about ants. While some ant species live their whole lives underground, other species live their whole lives in trees. While some ant species eat meat, others are strict vegetarians. So just because I couldn't find information about ants specializing on worms doesn't mean that there aren't any.

So why would ants who live in the same soil as worms not specialize on eating them? I think this might become more clear if we look at the foraging patterns of the two organisms.

Most ants forage away from their nesting site for food. This means that they aren't tunneling through the soil where worms might be found, but rather roaming the surface, where worms rarely go.

It is also interesting to consider worm foraging patterns. Surprisingly, worms don't tunnel randomly through soil. Most of the time earthworms stick to a series of tunnels they build in one small area. For this reason, it is unlikely that worms chance upon an ant nest regularly. I'm sure it does happen. But it's difficult to guess what the reaction of the ants to the worm (or the worm to the ants) would be.

Occasionally worms do come to the surface, such as during a big rain storm, or at night to quickly grab a leaf to pull into their tunnels for food. The reason that worms come out in the rain is still unknown, although it may be for mating purposes. Ants don't like foraging in the rain, so it is unlikely that they would encounter a worm at that time. For a great site detailing what's known about earthworms , see this site.

Some ants go out in groups looking for any animal to kill and bring back to their nest. If a group of foraging ants did come across a worm, I'm sure they'd tackle it. But it seems unlikely to me that they would specialize in hunting them down. A better example of an organism specializing on earth worms would be the planarian Artioposthia triangulata.

This was a very interesting question, and it shows you're thinking about ecosystem dynamics. Finding natural enemies requires a lot of this kind of thinking, and I'm impressed that you're already considering the subject at this level.


Thank you for your question!

John