How Do Spiders Capture Big Prey?
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.
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00:00 You've probably seen spiders catch insects that are smaller than they are in their sticky webs.
00:05 But did you know that there are some spiders that can catch prey that's much larger than they are?
00:10 And they do it by wrapping them in sticky strands of web and lifting them off the ground.
00:17 [music]
00:21 Now scientists have known about this behavior for some time, but it hasn't been very well studied.
00:26 So for the first time, a group of scientists took several of these spiders
00:31 and observed them doing this prey lifting behavior under laboratory conditions.
00:37 The spider built this web.
00:38 In the connection between the main frame of the web, which is the part dense of threads,
00:45 and the surface below, the spider spins these threads.
00:50 And these threads are actually the feature that sends signals to the spider
00:55 that something is hitting, something is passing below.
01:00 So the elastic energy stored in the frame, which is basically, we have to think about an elastic, you know,
01:07 so if you pre-tension an elastic, it will recall with an elastic force.
01:12 If the prey is small, so just one thread is necessary to lift it.
01:16 Unfortunately, when the prey is big, of course the one thread is not necessary.
01:23 But this is what actually poses a challenge to the spiders.
01:27 The logic is exactly the same as before.
01:29 So the spider produces threads as elastic and it pre-tensioned them.
01:35 Then it attaches this thread to the prey.
01:39 And this is pretty cool because it's one of the few cases where the spider is actively involved in the hunting by means of the web.
01:48 It's no more a trap, a passive trap, in the sense that the web works perfectly as it is.
01:54 But the spider is getting involved too.
01:57 Because normally the spiders are just sitting and waiting for the web, for a prey that enters the web.
02:03 And that's it.
02:04 As you can see, the structure of this web is particularly complicated.
02:08 There are different types of silk.
02:11 So each part of the web has its own silk for that specific function.
02:18 These are the supporting threads.
02:19 And as you can see, there are two types of threads.
02:22 Two threads in these supporting threads.
02:24 One thread is produced by a gland.
02:27 The other one is produced by another gland.
02:30 They are very same threads.
02:33 But this thread is coated with these droplets that are produced by another type of silk.
02:40 And we have three types of silk.
02:42 Where the spider joins together these threads, it uses this kind of cement-like silk, which is another type of silk.
02:50 So four different types of silk are used to produce this frame.
02:56 It also wraps the prey because it has also to mobilize locally the prey in order to avoid the prey to move too much.
03:03 And it uses another type of silk to wrap it.
03:07 Normally, material scientists go crazy with this because the spider is a perfect factory of silk.
03:13 It produces multifunctional materials in less than milliseconds, each one optimized for that property.
03:21 So it's crazy.
03:23 They are like machines.
03:25 They are super efficient.
03:27 And there are like 49,000 different species of spider.
03:33 Each one produces different type of silk with different properties up to the species, up to the individual.
03:39 So basically, we do not know nothing about silk.
03:41 When you start studying in-depth things, you realize that you don't know anything about them.
03:46 And I don't know, we use two species of spider.
03:49 But there are other species of spider, as I said before, that must be investigated from this point of view.
03:54 There are also other types of prey that may behave differently.
04:00 So this was just the first insights in this direction.
04:03 But there are tons of possible questions that can be answered.
04:09 So even though scientists now have a better idea as to how the spiders are able to trap large prey and actually lift it up off the ground,
04:18 there are still a lot of unanswered questions about how exactly the spiders make all these different types of silk.
04:25 And what are the limits of how they could use them?
04:29 [MUSIC]