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Earthworm having instinctive behavior?
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I noticed in rainstorms that when earthworms were caught in the water flowing down a paved road gutter that they all had their tails(?) shaped in the form of a hook. I assume to be able to catch debris and save themselves from the street drain. I presume that this behavior is instinctive as it occurred with each individual, having never seen any not adapting this posture. I was curious, has anyone studied whether earthworms have instinctive behaviors?

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"Instinctive" is not always well defined. Earthworms have innate behaviors that serve them well. Tactile stimuli applied to the posterior end cause them to extend the anterior setae and contract their longitudinal muscles, thus moving forward. Anterior tactile stimuli cause extension of the posterior setae, flattening of the tail (in some species) and longitudinal muscle contraction, causing movement to the rear. The neural underpinnings of these behaviors are fairly well established.

I am unaware of any studies examining worms forming their body into hook shapes. If this is an innate, hard-wired response to being submerged, or being caught in flowing water, it might serve the adaptive purpose that you suggest. We must be careful in asserting a motive, though; if worms do this it is not likely that they are trying to save themselves, as they likely lack the neural machinery to imagine their impending demise.

Thanks for a good question!

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Thank you for your answer. I thought instinctive because of the sheer numbers of individuals that I observed ~100 of all sizes that all exhibited the same behavior and while observing none that didn't. Also I accept your lack of neural pathways, and the behavior of forming the hook could be in response to finding themselves in flowing water, but wouldn't that response be classed as an instinct if it was innate in the youngest individual? I'm attributing age to size which also might be in error. Could just be an indication of how well they were fed. I suppose the question also depends on how instinctive behavior is defined. I'm using it in the sense that a wood duck duckling has all the necessary tools to feed itself just after breaking out of the shell and floating down from the nest (as much as 70m). In any case I was just curious and don't intend to run experiments on the worms I saw. :-) Thanks again for your answer.

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I was not asserting a lack of a neural pathway - just that I have not seen anyone suggest the neural underpinnings of this particular behavior. It must be neurally controlled. Your question is whether or not the behavior results from the innate determinants of the wiring of the nervous system, or instead reflects learning. I would guess that it is innate (and thus instinctive), but this could be tested. Maybe I'll get my students to run the experiment...

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