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Spider Leg Regeneration

Peter Hollinger's recent Lycosid submission sparked a question that I have never had answered. I am hopeful that the congregation of knowledgeable minds here @ BugGuide can help.

All I have ever known about spiders being able to regenerate lost legs is that they are only able to when they are very immature. That's all I know. Is that even true? Does anyone have any photographic evidence of the process? What are your opinions on the issue?

Thanks in advance! I await some juicy information!

Here is one image of a not-ye
Here is one image of a not-yet-released regenerated leg:
http://forum.canadianarachnology.org/viewtopic.php?t=383

-K

 
Wow!!
That is so amazing! That's just what I've been hoping to see! It's just...ahh, I'm speechless. Thank you, Kevin!

Tarantulas
Own and sell tarantulas. Female tarantulas are able to regenerate/replace limbs, long after adulthood and they can live over 20 years. Males however only survive long enough to reproduce and/or be eaten by the female, a general time span of a year or so at the most. Molting is stressful and living conditions should be adequate. Ex: tarantulas from temperate regions need their habitat lightly misted daily.

Even an adult may regenerate a lost limb.
I have an eleven year old female Mexican redknee tarantula, during her fifth year she lost a right rear leg while molting. Over the next four molts she not only regrew the lost limb but it grew to match her other legs perfectly. I dont know if this is true of all arachnids but I have heard of other tarantula species doing this.

 
Tarantulas
Yes, tarantulas are the main exception I had in mind when I said "In some of the more primitive spiders, though, females that live a long time may continue to molt after they reach adulthood, so there are some cases where an older spider could completely regenerate a lost leg." I think the average spider only lives a year or less, and doesn't have a chance to molt after reaching adulthood.

 
With Steatoda grossas in mind
I am sort of bewildered as to why Steatoda grossa adults don't molt more after reaching adulthood. Just like Charley said, the average spider only lives a year or less. So I understand why most spiders wouldn't have the need to molt more often. But grossa females live for a long time. It has always been disappointing to me as to why my favorite little Steatoda grossa (I call her 'The Queen') hasn't been able to regrow her two missing legs in over a year. She is a fully grown and reproducing female...and has never molted once since I've had her. S. grossa females will live upwards of five years in decent conditions...it seems to me that evolution should've stepped in by now. Or perhaps natural selection simply hints: "if you can't keep yer legs on, or get rescued by a human...then you're dead". My grossa is surviving just fine though, after I rescued her, and she should continue to thrive as long as she can manage to keep both of her back legs. I'm not sure how she lost legs I & II, but I bet it was a skiing accident.

Your impression is correct, from what I've read.
Spiders are able to gradually replace limbs as they molt. Adults of most species don't molt, so they aren't able to replace limbs. Since it takes a few molts to completely replace a limb, a spider would have to lose a leg in an earlier instar to do so. In some of the more primitive spiders, though, females that live a long time may continue to molt after they reach adulthood, so there are some cases where an older spider could completely regenerate a lost leg.

 
If replacement is gradual
then we should sometimes see a spider with one leg shorter than the matching one on the other side, right?

 
Yes
...as is the case in the image that prompted this post:

 
Cockroach regeneration
In case it may be of interest, there has been a significant amount of research done on cockroach regeneration. In contrast with most other arthropods, cockroach legs are regenerated in an all-or-none fashion. The molting cycle is stopped so that all of the tissue can be repaired and rebuilt, and when the next molt happens, a fully formed limb emerges. It may be somewhat smaller, but it has all of the segments and internal structures, muscles, nerves, etc, and the size of the limb will catch up with the matching one after another moult or two. The only notable difference is that the regenerated tarsus will only have 4 segments instead of 5 making this a nice way of knowing which roaches have had a difficult time getting to adulthood.

 
Wow!
That's really interesting- the ability to regrow the leg all at once. It's always been said that roaches (and Twinkies) will be nuclear holocaust survivors. I guess it doesn't hurt to be regenerative. :)

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