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

00:53sent signals to the spider that something is hitting, something is passing below.

00:59So the elastic energy stored in the frame, which is basically, you have to think

01:06about an elastic, you know. So if you pretension an elastic, it will recall with

01:11an elastic force. 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, but this is what

01:24actually poses a challenge to the spiders. The logic is exactly the same as before. So the spider

01:30produce thread as elastic and it pretensions them. Then it attaches this thread to the prey. And this is

01:39pretty cool because it's one of the few cases where the spider is actively involved in the hunting

01:47by means of the web. It's no more a trap, a passive trap, in the sense that the web works perfectly as

01:53it is, but the spider is getting involved too. Because normally the spiders are just sitting and

01:59waiting for the prey that enters the web. And that's it. As you can see, the structure of this web is

02:06particularly complicated. There are different types of silk. So each part of the web has its own silk

02:15for that specific function. These are the supporting threads. And as you can see, there are two types of

02:21threads, two threads in these supporting threads. One thread is produced by a gland. The other one is

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

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

02:44threads, it uses this kind of cement-like silk, which is another type of silk. So four different types of silk

02:53are used to produce this frame. It also wraps the prey because it has also to mobilise locally the

03:00prey in order to avoid the prey to move too much. And it uses another type of silk to wrap it. Normally

03:08material scientists go crazy with this because the spider is a perfect factory of silk. It produces

03:14multifunctional materials in less than milliseconds, each own optimised for that property. So it's

03:22crazy. They are like machines. They are super efficient. And there are like 49,000 different

03:31species of spider. Each one produces different type of silk with different properties up to the

03:37species, up to the individual. So basically we do not know nothing about silk. When you do start

03:43studying in-depth things, you realise that you don't know anything about them. And I don't know, we use

03:48two species of spider. There are other species of spider, as I said before, that must be investigated

03:53from this point of view. There are also other type of prey that may behave differently. So this was just

04:00the first insights in this direction, but there are tons of possible questions that can be answered.

04:09So even though scientists now have a better idea as to how the spiders are able to trap

04:14large prey and actually lift it up off the ground, there are still a lot of unanswered questions about

04:22how exactly the spiders make all these different types of silk and what are the limits of how they can use them.

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