Lecture: Spiders: golden orb-weaver: Narrator: Listen to part of a lecture in a biology class. Professor: Now when you think of the spider web, it's sticky, right? So if a fly or other insect lands on the web, it'll get caught. That's how the spider capture its food. But spiders actually produce different kinds of silk for different purposes. Not all of it is sticky. Some non-sticky silk is made to support the structure of the web. Let's look at the spider called the golden orb-weaver. Golden orb-weaver are found throughout the world that comprise many species of spiders. And they're called golden orb-weavers because of the color of their webs. Golden orb-weavers, like many spiders, spin sticky silk web to capture prey, but they also support their webs on a frame of non-sticky silk. Now, this might surprise you, but spiders have predators too and some of these predators can walk on this non-sticky silk. For example, some ant spieces are major predators of spiders, uh ... aside spiders are rich source of food, they're captured prey of this fighter, the protein with silk and spider itself. So ants based by the web to take the advantage of this food source, but ants rarely seen on the webs of some species of golden orb-weaver. How? Um, well, this is correct to commence to remember one species of golden orb-weavers and did a few experiments. They took silk thread in several webs and remove all the chemicals in this thread, one by one. And they found that ants wouldn't walk across the silk thread to eat feed when one chemical in particular is present, but would cross the silk of the chemical had been removed. This chemical was well known to researchers as it is produced by other insects of the chemical defense, but no one had investigated whether or not these spiders were producing it. Now, many organisms have chemical defenses against predators, but producing chemicals comes at a price. Right? It takes energy, uses up resources. So there has to be a good reason to spend that energy, um, could justify the cost. And as you might think, producing is enough of a reason to justify the cost. But the golden orb-weaver has interesting strategies for keeping those costs in check. I guess we could say. First, the researchers found that the chemical was absent from the webs of the smallest juvenile spiders. Female Student: Why is that important? Professor: Well, young spiders are so small, their silk threads aren't strong enough to support ants. So there's no need to produce this chemical. It's only when these spiders get big enough to produce silk that can support a predator's weight that they start spending resources to make this chemical. And second, although these spiders made thin neat thread for the part of the web to capture pray every day, orb-weavers use the same silk frame for a week or more. So it actually ends up being pretty energy efficient. Now the golden orb-weaver is a solitary. In social studies, spiders living together on the same web, methods of defence are different. See a bunch of ants were invading spider web, here, the main response would be a behavioral defense. Like together they might be able to trace the ends off, but for the golden orb-spiders, the chemical allows them to deter predators by themselves. Male Student: So they use only chemical defenses? No behavioral defenses? Because those are really common in animals, and they must have more than one predator. Right? I thought this chemical work to deter only ants. Professor: Good question. And I don't wanna mislead you. In fact, golden orb-weavers do use behavioral strategies to deter some predators. For example, they chased off a type of parasitic spider pray on them. Uh, we think because the parasitic spiders don't attack in large numbers the way ants do. But with their chemical defense, they can stave off large numbers of predators. And what's really interesting is, this study shows us one of the first examples the scene of something like this in an animal, a chemical defense that produced only when the pray needs it. In this case, when the spiders are so large that their webs can support predatory ants, and the ants become a threat. This adaptive use of a chemical defense, it's typically been documented in plants, not animals. Now I say this was the first time we've seen it, but there are over 4,000 spiders species in North America alone. So a finding like this is a good reason to study these species. This may not be an isolated phenomenon.