Do Worms Have Feet?

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“Do worms have feet?” asks Max in his submission. He does not include any photos, or any more context behind his question, but we will do our best to answer it nonetheless. The short answer is ‘no’. But if we take this a step further and ask why worms do not have feet, we get to the root of what worms really are to begin with. It would probably take studying the evolutionary history of worms to fully understand where this creature came from and to explain its footless state. Funnily enough, “a fossilized worm found” only a few years ago had scientists speculating that this creature may have been “key to the evolution of much of the animal kingdom”. So maybe we were all footless, legless worms at some point in time.

At the very least, the worm in this fossil is the earliest record we have of a bilaterian to date — a bilaterian being an organism whose body is vertically symmetrical. According to the article linked above, understanding “bilateral symmetry” is vital to understanding where our current animal kingdom came from. Humans are bilaterally symmetrical, so are our dogs and cats. Dinosaurs were too. Bilateral symmetry allowed organisms to move with intention (worms contracting their bodies to crawl across a surface), as well as develop an organized organ system. But as the Earth changed and environments demanded different things from our worm ancestors, evolution took center stage and changed their bodies to accommodate their new surroundings: they grew in size, developed different skins, and yes, grew limbs and feet!

Earthworm

With all of that said, we should note that earthworms, as well as many other worms and worm-like organisms, do possess setae: bristles that grow from each segment that do help with movement but are not classified as limbs. On the flip side, there is a class of marine annelids (annelida being the phylum of worms that earthworms also belong to) called polychaetes that have parapodia, which are not technically legs but act like them; they use them to paddle through the water. This is as close as you are going to get to a worm with feet.

Likewise, there are worm-like creatures with actual legs and feet, like many species of caterpillars and beetle larvae. Of course, the development of these limbs is a precursor to their metamorphosis into an insect with legs. In fact, the key difference between larvae and worms is this metamorphosis: larvae will transform into an insect, while worms stay worms; we should note that some worms do have a larval stage, like the horsehair worm, but they nonetheless mature into a fully-grown worm, and do not have a pupal stage (the stage during which a larva transforms into an insect inside a chrysalis). Then there are millipedes and centipedes, which have dozens of legs and feet, but although they are bilaterians and have long, worm-like bodies, they are not worms but are arthropods.

To conclude, why worms do not have feet is likely a more complicated question than it used to be, as is the question of worms really are, given that we have thousands upon thousands of species at this point. But simply put, worms are limbless organisms with bilaterally symmetrical bodies, and they contract the muscles in these bodies to move forward. They look deceptively simple, but there are hundreds of fascinating species of worms that have extraordinary bodies and abilities, from the “hammerhead flatworm” to the “bristle worm“. The reason worms do not have feet is because they do not need them, as opposed to the worms of ancient history that did and evolved to grow them. If an earthworm were to grow feet, it may not be able to tunnel through the soil as well. All of this is to say that, no, worms do not have feet, but given their track record Max might want to ask us again in a dozen million years and maybe our answer will change!

 

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Summary
Do Worms Have Feet?
Article Name
Do Worms Have Feet?
Description
"Do worms have feet?" asks Max in his submission. He does not include any photos, or any more context behind his question, but we will do our best to answer it nonetheless. The short answer is 'no'. But if we take this a step further and ask why worms do not have feet, we get to the root of what worms really are to begin with. It would probably take studying the evolutionary history of worms to fully understand where this creature came from and to explain its footless state. Funnily enough, "<a href="https://www.bbc.co.uk/news/science-environment-52019468" target="_blank">a fossilized worm found</a>" only a few years ago had scientists speculating that this creature may have been "key to the evolution of much of the animal kingdom". So maybe we were all footless, legless worms at some point in time.
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Author: Worm Researcher Anton

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