Meaning of a Death Curl

[becca81]

Something I've been curious about is the reason behind a tarantula curling its legs underneath it when it dies. I've heard different reasons as to why it happens, one of which being that the spider is dehydrated.

Does a death curl usually mean dehydration or does dehydration just always result in a death curl (instead of dying spread out)?

 

[Keith Richard]

I think that it's the gradual loss of bodily fluid pressure that "allows" the legs to curl inwards.....kind of similar to a hydraulic system that has a leak, the system components will default to the switch down position.

 

[cacoseraph]

Under Pressure?

this is a straight guess, but i believe tarantulas keep their legs extended via internal fluid pressure and contract them using more "regular" muscles.

so when they die, er, *something* would seem to drop their pressure. perhaps their circulatory system functions in part to maintain a positive pressure. i don't know. i don't even think TTKG specifically solves this question... but i'll check it again

 

[Code Monkey]

The extension of the legs is mostly a function of hydraulics. In a living spider you have a complicated system of shunts and such that allow them to regulate hemolymph pressure and where it's mostly going. For example, they can direct the hemolymph primarily into the abdomen when actively digesting food so that the nutrients are absorbed more rapidly. Or when active build up pressure in the cephalothorax by blocking flow back to the abdomen. In the short term the legs are "springier" and locomotor muscles bathed in hemolymph, in the longer term, since the hemolymph isn't being re-oxygenated, they tire out.

At any rate, once they're dead or in danger of dying, this regulation breaks down, pressure isn't being maintained, and the legs usually curl.

 

[Tescos]

I think cacoseraph sumed it up in laymens terms.
but....
I have had some spiderlings die in this and similar positions before now!

Don't know why? maybe the `pressure´ is not so great with spiderlings? or at least the contracting mucles are not maybe strong enough to pull in after the death? But why the sticking up in the air asthis just seems abit more abnormal to me?

Before anyone does ask....no this spider was not due a moult as it moulted just 2 weeks before its death and was seemingly fine afterwards so I don't think its a case of a new skin hardening under the old one.

 

[becca81]

That's the kind of stuff I'm talking about, Tescos.

I've also heard of adults dying who seem to just stop in their tracks, no death curl or anything. Could that just be a sudden death?

Now that I think about it - when I saw the video about the South American tribe eating what appeared to be T. blondi - its legs didn't curl when they killed it - they remained spread out (after it was opened up from the leaves).

 

[Jmadson13]

Now that I think about it - when I saw the video about the South American tribe eating what appeared to be T. blondi - its legs didn't curl when they killed it - they remained spread out (after it was opened up from the leaves).

I would however think that the dessication and heat of the flames would freeze the spider in that position. I'd imagine their are special circumstances in any case.

 

[Code Monkey]

I would however think that the dessication and heat of the flames would freeze the spider in that position. I'd imagine their are special circumstances in any case.

No to mention how cooking is bound to be increasing hydraulic pressure as you get those juices boiling, mmm, yum

There's also the matter of the death curl being sort of the equivalent of rigor mortis in us endoskeletal critters. Just as rigor mortis passes, if the spider doesn't curl while it's still alive and the legs are otherwise being held by the tarsi claws, you don't always get the curl. Ones that die on a piece of bark will often just be "frozen" in place, their legs held in a normal position. Think about it: if the curl is due to muscular contraction, once the muscles stop contracting, the legs won't curl on their own.

 

[becca81]

I would however think that the dessication and heat of the flames would freeze the spider in that position. I'd imagine their are special circumstances in any case.

This was before they were introduced to the heat.

Now that I think about it, when they were on the fire they began to curl. Eh, I need to go back and watch the video again.

 

[Apocalypstick]

Seems to me it would be more like our bodies. When our blood pressure drops, our extremities kinda shut down..or close off, so all the blood goes to the most vital organs...heart, brain etc. That explains why "sudden death" in a spider will not produce the 'death curl' we see in the legs as they die slower.

 

[Code Monkey]

Seems to me it would be more like our bodies. When our blood pressure drops, our extremities kinda shut down..or close off, so all the blood goes to the most vital organs...heart, brain etc. That explains why "sudden death" in a spider will not produce the 'death curl' we see in the legs as they die slower.

Except that spiders do not have a closed circulation system, so drawing analogies between your anatomy and theirs only counts if you already know what you're talking about

About the only two places they can really stop up hemolymph is between cephalothorax to abdomen and vice versa. Typically, hemolymph flows towards the cephalothorax along the dorsal side and back into the abdomen along the ventral side. Sudden death such that all hemolymph flow stops is only going to occur if you run one over with a truck or something similar. You can cut all their legs off, remove the brain, dissect their sucking stomach, and the "heart" will still continue to pump.

 

[becca81]

Hmmm - just thinking through things...

When the possible T. blondi was killed in the video, its legs remained outstretched until it was put on the fire. Could the fire have simply dessicated it / removed all the water from the body, causing the legs to curl?

Hence dessication being the reason for the curl in this example?

 

[Code Monkey]

I think people are really over complicating what is not a complex system:

Anything that causes the leg muscles to contract in the absence of something counteracting this musculature contracture (either hydraulic pressure or something physically holding the legs in place) will cause the "death curl".

If you heat them up the muscles are going to contract just like cooking a piece of bacon.

 

[Nerri1029]

I think people are really over complicating what is not a complex system:

Anything that causes the leg muscles to contract in the absence of something counteracting this musculature contracture (either hydraulic pressure or something physically holding the legs in place) will cause the "death curl".

If you heat them up the muscles are going to contract just like cooking a piece of bacon.

agreed


It's only the two major joints in the lags that have non-opposed muscles
If you notice closely the joints closest to the tarsa do not curl..

So I think the death curl is mostly caused at these two legs joints
where all the muscles in the spider are contracting equally but only here is there no muscles counteracting the one way contraction..

 

[becca81]

My original reason for asking the question was to find out if having a spider die in a death curl means that they are dehydrated (as has previously been implied in some threads.)

 

[Code Monkey]

My original reason for asking the question was to find out if having a spider die in a death curl means that they are dehydrated (as has previously been implied in some threads.)

Heh, well in that case, the answer is 'sometimes'.

I have seen adults that were severely dehydrated in "death" curls that upon rehydration returned to normal stances and were fine.

However, the death curl in and of itself doesn't mean the spider is dehydrated as (this thread should have made clear) there are many ways to get there.

 

[FrankSidebottom]

I think Gramastola rosea