When a Spider Loses a Leg, Does Its Whole Hydraulic System Lose Pressure?

Written by Joe Ballenger

This question came to us from Twitter, from user Katzider. It’s an excellent question for many reasons, not the least of which is because it’s about pet spiders. During our podcast with Mythwits, I expressed a little annoyance at the fact that there’s very little medical care for invertebrate pets and livestock. There are some very good economic reasons for this, but ultimately spider keepers are kind of on their own when it comes for veterinary care. Since spiders are popular pets, I think the questions Katzider sent to us are a great set of questions to focus on this week.

Before we jump into the meat of his question, we have to describe how spiders move and respond to injury. After that we’ll explain how a loss of fluid would affect movement, and discuss what precautions can be taken to save injured spiders.

For that last part, we’ll get to meet a brave little spider named Bob. But first…

How do spiders move?

Spider movement is extremely unusual amongst arthropods because it involves both the circulatory system and muscles. To extend legs, blood (or hemolymph, to be technical) is pumped into the legs which causes them to expand outwards. Bringing the legs in is caused by contractions of the muscles, which pushes blood back into the body cavity, and the process can start over again. There’s a great animation by the BBC which shows how this process works.

What happens when spiders hurt themselves?

When spiders lose legs, they typically lose them at predetermined ‘break points’…usually at a joint close to the body. These points have special muscles which clamp shut, to ensure the spider doesn’t lose too much blood. This process is called ‘autotomy’, and it’s completely normal. After all, you’d much rather lose a leg than a life.

To a spider, losing a leg isn’t a very big deal. Heck, some even voluntarily castrate themselves. Overall, there’s a slight lag in development time. Being short a leg or two (or six) is going to slow you down a bit, which makes prey harder to catch. So long as you’re able to catch prey, you’ll be able to recoup the resources you’ll need to regrow that leg. Easy-peasy.

Death Curl

Male tarantula in a death curl. Picture courtesy of Chris M. Morris, via Flikr. Image license: CC by 2.0

However…what happens if the leg is amputated before the break-point?

Well, the spider ends up losing a lot more blood before they’re able to eject the leg. When a spider loses too much blood, it has trouble moving. Often, injuries can remove so much blood that the spider goes into a stereotypical pose called a ‘death curl’ when things get really bad. Since extension of the leg is caused by an increase in blood pressure to the limb, the death curl is what happens when the spider’s blood pressure gets too low for it to extend the limbs.

In other words, if your spider looks like it’s going into a death curl…are really bad.

What can a spider owner do if your pet goes into a death curl?

Here’s where we meet Bob the Disabled Tarantula.

Bob the Disabled Tarantula is a Facebook page dedicated to one particular spider who lost their legs in an accident while escaping from their enclosure. It was caught on some sticky paper used to catch ants, initially losing six legs and dropping the seventh at a later point.

This is what a spider having a bad day looks like. Then again, it has a cricket...so things might be looking up. Pictures courtesy of the Bob the Tarantula Facebook page, used with permission.

This is what a spider having a bad day looks like. Then again, it has a cricket…so things might be looking up.
Pictures courtesy of the Bob the Tarantula Facebook page, used with permission.

A couple months later, Bob moulted and it’s legs are completely new.

Bob the Tarantula legs

This is the same spider as above, after the next molt. The legs have grown back, and all are the same size.

In pictures taken over a year later, there’s no trace of what happened.

Bob’s owner did everything right in terms of medical care. The spider was placed in a clean container, with increased humidity and access to water. This allowed Bob to re-claim the water lost from the injury, and reduce any further damage caused by dehydration.

The injury obviously made it more difficult for the spider to capture prey…but spiders are pretty tough. Because Bob was able to eat, Bob was able to recover and live a normal spider life.

If you want to make your own tarantula ICU, this video is a great explanation of how this process works:

Bottom line

If a spider is injured, it’s possible it will have trouble moving because of the hemolymph loss. This loss of hemolymph causes some locomotor issues because of the unique way that tarantulas move. However, if care is taken then the spider can recover from some pretty grievous injuries.

Also, I’d like to thank the Bob the Disabled Tarantula Facebook Page for giving us permission to use some of the pictures from their website.

This entry was posted in Education, Physiology and tagged , , , , , , , , , . Bookmark the permalink.

7 Responses to When a Spider Loses a Leg, Does Its Whole Hydraulic System Lose Pressure?

  1. Gary Dunn says:

    Just wanted to follow up Bob molted about a month after losing all but one leg. He dropped the last one himself and he only was left with one. This is great article and alot of information. Remember this was an accident and should have never happened. And I thank you for the article. Bob btw is an OBT and he is quite the fighter. He did in one month what no other spider had done before one two maybe but not seven. So thanks again
    Gary Dunn
    Owner of Bob the now healthy tarantula


  2. Diana says:

    Just found this little fellow spider in my bathroom, and i was about to kill him whrn i realised that he has lost a leg …
    I am terrified of spiders, but this one had melted my heart.
    Bottom line , i want to help him recover.
    Where do i start?
    Thank you for your time


    • He’ll just regenerate his leg over time. So no worries!


      • danharkless says:

        Polistes fuscatus: no, it’s not quite that simple. The spider can only regenerate the leg if it hasn’t yet grown to full size. From the UK Safari website: “A spider can go through 20 or more instars before it reaches its full, adult size. Not only does the shedding allow for growth, but it will allow for regeneration too. If a spider is unfortunate enough to lose a leg, then provided it still has at least one more moult left in its life cycle it’s able to grow a new leg. In most species the new leg is thinner and shorter than the original leg. It can take two or three moults until the regenerated limb matches the original in appearance.”

        Diana, congratulations on becoming enlightened about spiders being our friends. I, too, used to kill spiders on sight (via smashing, hair spray can flamethrowers, etc. 😢), out of a mistaken and irrational fear that they were out to get me and bite me, but in recent years, I have become a huge spider fan. I always feel terrible when a spider loses a leg in the course of me saving it from drowning in the shower or whatnot, but better to live on with 7 legs than to die an early and needless death.

        Joe Ballenger, thank you for this post. It answered the question I had that was prompted by a line in “Blade II”, when one of the vampire characters claims that if a spider loses a leg, the leg continues to twitch and move by itself, which is something I’ve never seen even though I’ve seen spiders lose legs on more than one occasion. Your explanation of how spider leg movement works confirms my suspicion that that line is in error, since with the hemolymph system disconnected, the leg would only be able to contract, at best, and probably only once at that without having an electrical current applied.


  3. xmegatron says:

    I have a QUESTION in a territorial fight who wins a male (NOBLE FALSE BLACK WIDOW SPIDER) or a male joro spider.


  4. xmegatron says:

    Who wins in a fight over territory a male joro spider or a male (NOBLE FALSE BLACK WIDOW SPIDER)😁😁😁😁😁😁


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