Venatoria jumping

[The Snark]

If anyone could explain this I would seriously appreciate it.
Only observed in the wild at night. H. Venatoria that get startled and make their dashes will sometimes suddenly pause then jump straight up, as high as about 10 inches. Then back to boogie mode. I observed one on a road that did this four times in the period of around 30 seconds.
What gives? ?????????????????????????????????????????

 

[Jonathan6303]

Why they jump? Escaping mechanism as far as I now of.

 

[The Snark]

Why they jump?

Yes. The only two reasons I can come up with is some neurological reflex or the jump is used to reposition it's legs or clear it's claws. Notable is the jump momentarily compromises it's normal mode of defense, the dash to escape a predator. Remotely possible is the jump offsets an impeding attack by it's most common enemy, night birds. Perhaps something similar, the opposite of hiding in plain sight, stay motionless and predators like geckos can't see them as those predators are reflex hunters that require motion by the prey. So pop up in the air and a night bird misses it's target.
I've only observed the jump on flat surfaces. Never on sloped or vertical surfaces where I usually observe them.

 

[Jonathan6303]

Yes. The only two reasons I can come up with is some neurological reflex or the jump is used to reposition it's legs or clear it's claws. Notable is the jump momentarily compromises it's normal mode of defense, the dash to escape a predator.

This is interesting. Especially because it jumped up not away. Well common predators of spiders are birds, small mammals, inverts, insects and so on. So I would lean towards reflex because if a bird can fly I don’t understand why a spider would jump up instead of away. There is also many other factors that I am not taking into consideration.

 

[The Snark]

It's strange because it's so out of whack with it's normal modes of locomotion.

 

[The Snark]

Another possibility occurred to me. A pressure relief valve.

Locomotion of most spiders and insects is through hydraulic pressure. Pistons as on an excavator that push in opposing directions. The excavator extends the arm, the pressure must be relieved for the pressure on the other end of the ram to retract it.
So maybe the jump is a reset, allows the pressures to equalize on the rams. ??

 

[Jonathan6303]

Another possibility occurred to me. A pressure relief valve.

Locomotion of most spiders and insects is through hydraulic pressure. Pistons as on an excavator that push in opposing directions. The excavator extends the arm, the pressure must be relieved for the pressure on the other end of the ram to retract it.
So maybe the jump is a reset, allows the pressures to equalize on the rams. ??

Was thinking about that to. We most also discover whether or not this is an escape mechanism or not. Do they do this while not endangered.

 

[Jonathan6303]

There was a wolf spider(don’t remember the name but it had white spots like d triton and had a red streak on its abdomen on the heart mark. it also made a green egg sac. It was about 6-7 mm) that exhibited this behavior and the two things that popped in my mind was it is either a Salticidae or one of the Oonopidae genuses that are believed to jump. Once I figured out it was a wolf spider I thought it was an escaping mechanism.

 

[Edan bandoot]

Take a video of it

 

[Jonathan6303]

Now that I think of it there was this other spider that was green with a silver abdomen. the abdomen was kind of triangular, short legs, was in a tree, (and wasn’t leucauge venusta I think) and was a male who jumped like crazy when I cupped him.

 

[The Snark]

Do they do this while not endangered.

Moot. I've only observed this when I was in close enough proximity to have caused fright.

Take a video of it

Right. I'm lucky if I remember to carry my camera and get still shots. Going out and night and prowling around just to find them is tricky. Being ready and able to take a video in the dark on the rare occasions they do the pop up? Probably be easier to pick up a blob of mercury with a pair of pliers.

 

[Poonjab]

The H. Venatoria has a condition called myotonia congenita, a disorder that affects the exoskeleton, which is used for movement. ... The sudden stiffening of the exoskeleton as the animal attempts to flee sometimes causes them to spring straight in the air, which looks a bit like they have taken off like a rocket, from freight.

 

[Tarantuland]

The H. Venatoria has a condition called myotonia congenita, a disorder that affects the exoskeleton, which is used for movement. ... The sudden stiffening of the exoskeleton as the animal attempts to flee sometimes causes them to spring straight in the air, which looks a bit like they have taken off like a rocket, from freight.

Can you link to this? I can't find anything saying the H venatoria or any spider having this which makes me think you're foolin

 

[The Snark]

While a specific condition such as a congenital disorder is possible if unlikely, myotonia or similar neuromuscular conditions are certainly a possibility. As a gross example, muscle cramps which become more common in trained athletes where the envelope gets pushed to an extreme degree. As example, at Olympiads it's relatively common for contestants to drop out of races with cramping simply because they hadn't undertaken enough proper warm up exercises. And broadly speaking, the heteropoda genus fits well within the description of Olympic level sprinters.

I'm considering firing off an inquiry to Senkenberg in the off chance myotonia has been noted among arachnidia.

 

[The Snark]

Well, what we have here is a dead end. I fired off Has the general condition of myotonia ever been noted among arachnids? to Dr. Jäger and the reply was:
" I have no idea. Not even a clue who you could ask."

 

[AphonopelmaTX]

Well, what we have here is a dead end. I fired off Has the general condition of myotonia ever been noted among arachnids? to Dr. Jäger and the reply was:
" I have no idea. Not even a clue who you could ask."

That sounds about right, but you have to respect Jäger's honesty. People send pictures and ask for explanations of unusual observations to the e-mail listserv of the American Arachnological Society fairly regularly just to get "I don't know" as a response. The fact of the matter is that spiders are just not as well understood as you might think, but it is always good to ask someone just in case.

I've been trying to imagine what it is that was seen. As far as I know it would be physically impossible for any spider to leap 10 inches straight up just because they don't have the muscles to do so like a grasshopper does. Even in jumping spiders it is the distance, not the height, of their leaps that are impressive. But you never know what is or isn't possible until you find someone else that has seen and studied the same thing as you.

 

[The Snark]

As far as I know it would be physically impossible for any spider to leap 10 inches straight up just because they don't have the muscles to do so like a grasshopper does.

Agreed. I've wracked my brain about that for several years. mechanically it is possible, obviously,

but well outside any ordinary function. So my theory is it's an abnormal neuromuscular condition, possibly a disorder. Which leaves me back at the starting gate.
Note in the image there is flexure between femur and tibia and a fully developed patella that the other animals don't have. So a third class lever can produce that motion in the absence of lateral or opposing forces..