How Do Spiders Capture Big Prey?

Live Science

Ingenious web construction and energy stored in stretched silk strands lend spiders super powers to lift animals too heavy for the spiders' tiny muscles to support.

Transcript

00:00You've probably seen spiders catch insects that are smaller than they are in

00:04their sticky webs. But did you know that there are some spiders that can catch

00:08prey that's much larger than they are? And they do it by wrapping them in sticky

00:13strands of web and lifting them off the ground.

00:20Now scientists have known about this behavior for some time, but it hasn't

00:25been very well studied. So for the first time a group of scientists took several

00:30of these spiders and observed them doing this prey lifting behavior under

00:35laboratory conditions. The spider built this web. In the connection between the

00:39main frame of the web, which is the part dense of threads, and the surface below,

00:46the spider spin these threads. And these threads are actually the feature that send

00:54signals to the spider that something is hitting, something is passing below.

01:00So the elastic energy stored in the frame, which is basically we have to think about

01:06an elastic, you know, so if you pretension an elastic, it will recall with an elastic

01:11force. If the prey is small, so just one thread is necessary to lift it.

01:16Unfortunately, when the prey is big, of course the one thread is not necessary,

01:23but this is what actually poses a challenge to the spiders. The logic is exactly the same as before.

01:29So the spider produce thread as elastic and it pretensions them. Then it attaches this thread to

01:38the prey. And this is pretty cool because it's one of the few cases where the spider is actively

01:45involved in the hunting by means of the web. It's no more a trap, a passive trap in the sense that

01:51the web works perfectly as it is, but the spider is getting involved too. Because normally the

01:58spiders are just sitting and waiting for the prey that enters the web. And that's it.

02:04As you can see, the structure of this web is particularly complicated. There are different

02:09types of silk. So each part of the web has its own silk for that specific function.

02:17And these are the supporting threads. And as you can see, there are two types of threads,

02:22two threads in these supporting threads. One thread is produced by a gland. The other one

02:28is produced by another gland. The very same thread, but this thread is coated with these droplets

02:37that are produced by another type of silk. And we have three types of silk. Where the spider joins

02:43together these threads, it uses this kind of cement-like silk, which is another type of silk. So four

02:52different types of silk are used to produce this frame. It also wraps the prey because it has also

02:58to mobilise locally the prey in order to avoid the prey to move too much. And it uses another type of silk

03:06to wrap it. Normally, material scientists go crazy with this because the spider is a perfect factory of

03:12silk. It produces multifunctional materials in less than milliseconds. Each one optimise for that property.

03:21So it's crazy. They are like machines. They are super efficient. And there are like 49,000 different species of

03:32spider. Each one produces different type of silk with different properties up to the species, up to the individual.

03:39So basically, we do not know nothing about silk. When you start studying in-depth things, you realise

03:45that you don't know anything about them. And I don't know, we use two species of spider, but there are

03:50other species of spiders, as I said before, that must be investigated from this point of view. There are

03:55also other type of prey that may behave differently. So this was just the first insights in this direction. But there are

04:03tons of possible questions that can be answered. So even though scientists now have a better idea

04:12as to how the spiders are able to trap large prey and actually lift it up off the ground, there are

04:18still a lot of unanswered questions about how exactly the spiders make all these different types of silk,

04:25and what are the limits of how they can use them.

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