“What is this yellow, boxy, stretchy, little snake-like thing?” asks Catherine in her submission regarding the organism pictured below. “I found it hanging from the dashboard of my truck in Seattle. At first I thought it was a rubber band, but on closer inspection I came to realize it had a sort of mouth looking opening on the end and was spotted with specks. It is unlike anything I had seen before. It has no bones, so not a snake. It lost the yellow color it had while submerged in water. Found in Seattle, Washington. Thank you.” To start with, we thank Catherine for the photo she sent in: you can really see the “boxy” nature of the creature’s body, by which we think Catherine means that it seems to be somewhat flat, giving it a clear underside and topside, unlike most worms.
Based on this, we think Catherine found a flatworm in her car. There are tens of thousands of flatworms, and we do not know exactly which one Catherine found. They are generally not dangerous to humans when found roaming freely. There are parasitic flatworms (like the tapeworm), but those will typically pass from organism to organism and do not roam freely to try and find a host. Most terrestrial flatworms are predators, and will eat a range of little critters, from invertebrates like snails and worms (including other flatworms), as well as arthropods like millipedes and centipedes, and insect larvae. Many species of flatworms will kill their prey by secreting a toxic fluid. This fluid will not cause a human being, or any animal that is significantly bigger than the given flatworm, but it can cause an allergic reaction resulting in pain, irritation, and rashes. And they will also secrete this fluid if they feel threatened. For that reason, we suggest Catherine avoid touching the flatworm.
What we recommend doing is removing the flatworm from the car using a stick or dustpan (for example) and placing it outside, where it will continue on its way, minding its business. It is likely the flatworm only ended up in the car by accident, either coming in on someone’s shoes or clothes, or through a vent. We do not know why this flatworm seemed to change color when placed in water, but Ben Panko writes about a “flatworm that changes color” when exposed to the sun, so perhaps the phenomenon Catherine witnessed is related to that.
In conclusion, we think the worm Catherine found in her car was a flatworm of some kind. They are not significantly harmful to humans or pets, though one should still avoid making physical contact with them, given the risk of the flatworm secreting their toxins. We hope this helps, and we wish Catherine the very best.
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