A reader recently sent us a picture of some brown worms that she found outside, and asked us if we could identify these worms and inform her whether they might attack earthworms. We are reasonably sure that they are flatworms!  Here’s the picture she sent us:

She said these worm-like organisms are around 1/4 inch long, while the largest was closer to 1 inch long.  She has noticed various colors, including black, but most are the brown color shown in the photograph. So what are these creatures? Our reader wants to know if they are nematodes, and if they attack earthworms.

Did our reader discover nematodes? There are over 25,000 species of nematodes, over half of which are parasitic. Nematodes have adapted to almost every ecosystem, and so they are present in every corner of the Earth. However, we don’t think that these are nematodes. We suppose it is possible, but we think it is more likely that they are flatworms!

Terrestrial flatworms, or land planarians, make up the Geoplanidae family. Unlike nematodes, terrestrial flatworms have a narrow and specific habitat distribution. They lack water-retaining mechanisms, which makes them sensitive to variations in humidity.  Since land planarians have very specific ecological requirements, the presence or absence of certain species in a given habitat can be used to indicate the conservation status of that environment.

Most terrestrial flatworms are carnivorous and active predators of other invertebrates, like earthworms, snails, and slugs. They are also sometimes cannibalistic, hunting and eating other terrestrial flatworms.  Land planarians hunt by using chemical signals to detect their prey. For example, they follow the mucus trail from slugs, snails, and land planarians to find their prey and attack. Next they attack and capture their prey using physical force and the adhesive properties of their mucus. So, to answer our reader’s second question: Yes, the organisms she discovered do eat earthworms, as well as other invertebrates.

To conclude, one of our readers wrote to us about some small worm-like organisms she came across. She thought they could be nematodes, which is a possibility. However, we think the organisms are probably terrestrial flatworms, not nematodes.

 

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