Seven-Legged Spider

jsloan · Jul 30, 2009

Caught this guy in a pitfall trap earlier this month. It seemed to be missing a leg and I thought nothing of it. A couple of weeks later it molted and the leg didn't regenerate, so I took a closer look. Apparently, there never was an eighth leg! The coxal segment that would have remained when a leg is lost just isn't there.

This is a true 7-legged spider: four on the right side, three on the left side.

View attachment 79539

View attachment 79538

I took this one under the microscope, through the side of the plastic vial I have the spider in. The spider wouldn't hold still for long, and my camera battery was failing, so this is the best shot I have right now of the underside.

View attachment 79540

jsloan · Jul 30, 2009

Here's the molted skin for a closer view:

Spider-Spazz · Jul 30, 2009

Holy smokes!
Thats amazing! Thanks for the pictures!

ZergFront · Jul 30, 2009

Still a nice spider non-the-less. Looks like a male crab spider of some sp. Is it still alive or do you use the toxic pit traps to catch pin-up specimens?

One of my jumping spider slings lost a front leg in a fight with a sibling - but I saw him catch a fly this afternoon, so looks like he'll be ok. Spiders are very versatile.

ErikWestblom · Jul 31, 2009

That's awesome jsloan! Never seen anything quite like it! It's the 5-legged calf of spiders

jsloan · Jul 31, 2009

ZergFront said:
Is it still alive or do you use the toxic pit traps to catch pin-up specimens?

It's still alive. I'm keeping it that way until it becomes an adult (I estimate one molt to go), and then I'll try and ID it to species.

jsloan · Jul 31, 2009

ErikWestblom said:
That's awesome jsloan! Never seen anything quite like it! It's the 5-legged calf of spiders

Somewhere, in one of my vials, I have a 7-eyed crab spider: one of the AME is missing - not poked out, but it's like it was never there, just smooth cuticle where the eye should be. If I ever find it again I'll post a picture of that, too. Unfortunately, it's in a large "community vial" from about 5 years ago, mixed in with about 50-60 other spiders, all caught in the same week in the same pitfall trap, all waiting to be identified. And, I have a whole bunch of vials like that. So, like I said, if I ever come across it again ...

8+) · Jul 31, 2009

Amazing!!!

I actually wrote an instrumental song recently in 7 that I titled "Seven Legs". I was thinking it would have to be a spider that had lost a leg, but now I guess not necessarily!

What · Jul 31, 2009

Coxal relocation following the loss of an adjacent coxa in L. variolus

jsloan · Jul 31, 2009

What said:
Coxal relocation following the loss of an adjacent coxa in L. variolus

Interesting. That might explain the reddish line on the molted skin, between the palp and leg I/II. That might be what's left of a scar where Leg I was originally, perhaps? Too bad the paper doesn't suggest ways in which a spider might lose a coxal segment in the wild. I find it hard to believe a spider could remove it's own coxa, but maybe it's possible somehow. It certainly couldn't have grabbed and removed it with its mouthparts, which aren't in a position to do that.

Something else the paper didn't mention or measure: any changes in the length of the sternum on the amputated side. Notice in the picture above how the outer rim of the sternum is shorter on the side with only three legs. Too bad the paper didn't include photos of either the spiders or their shed skins. Those might have been interesting to see.

Thanks for the link. What a strange experiment for someone to do!

cacoseraph · Jul 31, 2009

heh, i was reading down the thread hoping nobody had posted the latro article

blast you, what!

Malhavoc's · Jul 31, 2009

noticed it hasnt been said yet...

crab spiders are ambush hunters with their foward legs being elongated for snatching prey. if this crab spider truely did loose leg I with coaxa and the other legs moved into to take its place..(and maybe the camera angle is off) but then wouldnt that mean that leg II that has moved into its place has adapted to become elongated aswell?

jsloan · Jul 31, 2009

Malhavoc's said:
if this crab spider truely did loose leg I with coaxa and the other legs moved into to take its place..(and maybe the camera angle is off) but then wouldnt that mean that leg II that has moved into its place has adapted to become elongated aswell?

I suppose that might be possible, but from what I can see the front leg on the left side is the same size as Leg II on the right, so it doesn't appear to be any longer than normal. I'll have to measure it under magnification to know for sure, of course. But, it seems from just looking at it that leg II is already long enough to act as a sufficient substitute for Leg I; or, in the case of this spider, a sufficient substitute for the pair of legs I and II.

Malhavoc's · Aug 1, 2009

jsloan said:
I suppose that might be possible, but from what I can see the front leg on the left side is the same size as Leg II on the right, so it doesn't appear to be any longer than normal. I'll have to measure it under magnification to know for sure, of course. But, it seems from just looking at it that leg II is already long enough to act as a sufficient substitute for Leg I; or, in the case of this spider, a sufficient substitute for the pair of legs I and II.

Hihi, I wasn't quite sure it is hard to tell on the angle of the pictures but by all means please do measure. the adaptation of these beasts is mind blowing with or without the leg being bigger

as for what could of happen to loose the leg in the wild I can only assume it attacked prey a little larger then it could hand.e or a naturual spider predator simply gave it a good yank at the right point. too many possiblities to know for sure shame the spider can't tell us

soozayn · Oct 7, 2016

jsloan said:
Caught this guy in a pitfall trap earlier this month. It seemed to be missing a leg and I thought nothing of it. A couple of weeks later it molted and the leg didn't regenerate, so I took a closer look. Apparently, there never was an eighth leg! The coxal segment that would have remained when a leg is lost just isn't there.

This is a true 7-legged spider: four on the right side, three on the left side.

View attachment 79539

View attachment 79538

I took this one under the microscope, through the side of the plastic vial I have the spider in. The spider wouldn't hold still for long, and my camera battery was failing, so this is the best shot I have right now of the underside.

View attachment 79540

soozayn · Oct 7, 2016

I have been removing spiders from my house (my daughter has arachnophobia) & putting them into an outbuilding for about 12 years. I now have quite a large family of spiders out there & the vast majority of the current ones have only 7 legs with no sign whatsoever of there ever being an eighth leg. Like yours they have four legs on the right side & only 3 on the left. I'm wondering if this is a genetic mutation due to interbreeding or something?

The Snark · Oct 7, 2016

soozayn said:
I have been removing spiders from my house (my daughter has arachnophobia) & putting them into an outbuilding for about 12 years. I now have quite a large family of spiders out there & the vast majority of the current ones have only 7 legs with no sign whatsoever of there ever being an eighth leg. Like yours they have four legs on the right side & only 3 on the left. I'm wondering if this is a genetic mutation due to interbreeding or something?

I asked an arach expert that same question a while back. His reply is a census would have to be taken and records kept. Could you possibly do this? How many spiders of how large a population are affected, over what period of time is this occurring and similarities in the incidences.

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