How could spider sex unlock secrets to engineering?
Wednesday 8th Feb 2023, 12.30pm
Not everyone is the biggest fan of spiders…we know that. They might not be the first thing that springs to mind when it comes to romance, either! But, you’ve got to admit, when it comes to engineering, they’re pretty incredible. Capable of making up to seven types of silk, and able to sense vibrations through thousands of ‘ears’ on their legs, there’s a lot we can learn from spiders when it comes to new materials and sensor technologies. So, on this year’s Valentine’s episode of the Big Questions Podcast, we’re asking arachnologist Dr Beth Mortimer how spider mating rituals could help us become better engineers.
Emily Elias: While some people might find spiders terrifying, their eight legs have a lot to teach us, and their sexy times are probably that you’ve never really thought about, but, looking at their mating rituals might actually help make us better engineers.
On this episode of the Oxford Sparks Big Questions Podcast, we are asking, “How could spider sex unlock secrets to engineering?”
Hello, I’m Emily Elias and this is the show where we seek out the brightest minds at the University of Oxford and we ask them the big questions, and for this one we’ve found a researcher who has spiders in her head, and, her heart.
Beth Mortimer: So I’m Dr Beth Mortimer, I am a biologist and I go by lots of different names in terms of describing what I do. So to some people I’m an arachnologist, that means someone who studies spiders. To others I would say that I’m kind of interested in biology and engineering. So I study what’s called biomechanics, but really I’m interested in animal behaviour, how they use information and that includes studying spiders as well.
Emily: Some people might be squeamish to spiders, you’re just like, all in for it.
Beth: (Laughter) So, some people are squeamish to spiders, I would say that I’ve always been fascinated by them, even as a child, but just to reassure people that if I do get a spider on me, that I wasn’t expecting, I do still get the same reaction everyone does, which is, “Get the spider off me.”
Emily: Fair enough, okay, why are spiders important to study then?
Beth: So spiders are really important members of the ecosystem. I think I’m drawn to them because they are such amazing engineers basically, in terms of what they’re able to do. So if you think about spiders as a group they’re actually quite unusual in that they’re almost exclusively predatory.
So any other kind of major groups, remembering that there’s over 40,000 species of spiders, they’re almost all predators. So they’ve really gone all out in being able to catch other things to eat, which is mostly other insects. But the way that they’re able to do this is that they’ve really invested in their engineering capability.
So what I mean by this is, they make their own materials. So, I study female spiders that make up to seven different types of silk material, that they use for lots of different biological uses including catching prey. But also that they make these beautiful and elaborate webs in order to use those materials to the best that they can be.
So spiders really are fascinating for those two reasons, but I’m really interested in kind of, learning from them as engineers. Using a biological approach, so trying to understand their biology.
Emily: What about other parts of the spider that are really interesting mechanically to you, what might those be?
Beth: Yes, so one of the great things that I look at, is that their web isn’t just there to capture prey, but actually it transmits information to the spider as well. So, vibrations that move through the web to the spider.
And the way that they sense these vibrations, is using their legs, and effectively they have thousands of ears distributed across their legs which they use to measure how the web is moving; which moves their legs, and then they detect basically how their legs are moving using these thousands of different sensors that they have.
Emily: Wait a second, let me get this straight. So, a spider’s legs are like ears?
Beth: So, it really depends on what you mean by an ear, just to give a (Laughter) scientific answer to that question. So, the thing to bear in mind here is that ears typically, what we mean by an ear, is something that is able to detect airborne sound. So that’s what our ears are really good at doing. We detect how the air is vibrating, we pick that up with the membrane that’s in our ear, that then goes through to our middle and inner ear.
Instead what the spiders are doing is detecting vibrations that move through solid surfaces essentially. So, it’s not vibration through air but vibration through solid materials. So whatever surface they’re standing on, for example a web, that moves, that movement is then transferred to their leg, where they are standing on the surface, and then with these sensors they are able to detect how much their legs are moving.
Emily: So, some spiders are quite small, some are quite scary and big, I mean how do you go about studying these little slits in their legs?
Beth: So in my lab, I have hundreds of different spiders at the moment, and we have a variety of different species. So, my approach, although it’s not kind of looking at all species of spider to get that really solid evolutionary understanding of it, I have basically different spiders that are different shapes and sizes. And I try and understand how factors that vary between them, such as their size, such as their weight; how that affects how their body moves when it’s on a vibrating surface.
So the small spiders I have, people might be familiar with them, kind of in September time of year, you see these orb webs, these two dimensional webs that appear in your garden with these beautiful little spiders in the middle. They are garden cross spiders, and we collect some of these spiders in the Oxfordshire countryside in August and September and then then we have them in our lab for web building and animal behaviour experiments.
But we also have bigger orb weavers as well, so we have golden orb weaver spiders. In the wild they can make webs that are up to two meters across, and these webs are very good at catching bats and birds. So really, really impressive animals that make these hugs two-dimensional orb webs to capture prey.
Lastly, we also have some tarantula spiders. So we’ve got some Brazilian black tarantulas, as you say, a little bit more chunky, a little bit more hairy, but they provide a different type of body, that then we can see what effect that has on the ability for these vibrations to move through their body as they’re stood on a vibrating surface.
Emily: So, what kind of behaviours do you end up looking at?
Beth: So, I’m really interested in how they respond to vibrational stimuli. So essentially we can play vibrations to them, whether that’s something that we’ve generated ourselves, or whether it’s something that’s actually generated by a prey item for example, and you see how they respond to it.
So I’ve mostly focused on predatory responses, so, what type of vibrations, what type of time patterns, what type of frequencies are important for spiders being able to look for and find prey items, but it’s also interesting in the concept of courtship.
So actually male spiders will generate vibrations that will then move towards the females that they detect, and they use that in order to find prey as well. So, although I’ve not studied that directly, that’s something that’s also really important from vibration sensing with spiders.
Emily: How do spiders do it?
Beth: (Laughter) So, in terms of how spiders kind of find each other and do courtship related to vibrations, the males have quite a tricky job because the females are extremely aggressive. So, I told you before that spiders are almost exclusively predatory. This means they’ve really been selected for being quite aggressive in their response to vibration, being able to find and detect prey items, but also get to them very quickly and being able to eat.
So the predator that can respond quickly to prey that might be there is going to do really well. So especially for these spiders that are larger, which tend to be female, they’re very aggressive so the male has quite a hard job in basically saying to the female, “Please don’t eat me, I’m a male spider of the same species as you, and I would like to mate with you.”
So for some species of spider that are males, they invest quite a lot on very repetitive, very long term vibrational signals, that they’ll play to the female, sometimes over several hours, in order to convince the female he can get close and mate with her.
So although it really varies across spiders, for a lot them, they will have a vibrational component to their courtship routine which is essentially serenading the female ready for mating.
Emily: And how do they make that vibration?
Beth: Again, it really varies across different spider species. So, for some of them, they might have parts of their body that they rub against each other. That would be what we call stridulation. And by doing that they basically vibrate their legs which then vibrates the surface that they’re on.
For other spiders they might drum their legs or their appendages against the surface. So essentially, they might be literally drumming the surface that they’re on. For others they might tremulate a body part. So they’re literally kind of moving a body part up and down and as they’re moving their body and their legs with this tremulation that then goes through into the surface that they’re on.
But lastly especially with the web building spiders you might have a kind of purposeful kind of plucking behaviour. So you have some time of movement on the silk material that’s essentially analogous to a kind of plucking.
So there’s a whole variety of different behaviours, but the key thing here is that each species will have a very specific pattern or way of generating this vibration that allows the female to know that’s it’s a male of her particular species that’s there.
Emily: So, what do you gain from looking at how spiders’ legs vibrate?
Beth: I’m really interested in kind of how we can learn from spiders to help with engineering and challenges that we have in terms of making our own material or sensors.
So just to give an example of that, spiders really are really, incredibly sensitive to this type of information source. So simply by standing on a vibrating surface they’re really good at not only determining if something’s there, but knowing where it is, and knowing how it’s appropriate to respond.
Now if you’re able to learn from how spiders do that so quickly and so efficiently, then you can start to make sensors or sensory technologies that are able to do similar types of tasks. So, a big problem that we have in engineering is how you’re able to get information that’s useful relative to background noise that isn’t useful. So, by looking at the mechanisms that spiders use, you can start to get inspiration for how you might be able to design these types of systems.
And one thing I particularly have in mind would be a vibration sensor that you might be able to embed into robots, or a series of vibration sensors so that then they can start to get information about externally generated movements but also their own movements as well.
So the idea here is to learn from spiders, understand the mechanisms that they use, and then take what’s useful as inspiration to help design new technologies and engineering for various applications where you can use vibrations for useful information.
Emily: Who would have guessed we have so much to learn from a spider’s legs?
This podcast was brought to you by Oxford Sparks from the University of Oxford, with music with John Lyons and special thanks to Beth Mortimer. Tell us what you think about this podcast. You can find us on the internet, we are @oxfordsparks, plus we have got a website OxfordSparks.ox.ac.uk.
I’m Emily Elias, bye for now.
Transcribed by UK Transcription.