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Emily Graslie: We're back here at the Field Museum with Dr. Petra Sierwald who is an associate curator in insects and today, what are we going to talk about?

Dr. Petra Sierwald: Spiders, of course, my favorite.

Emily: But spiders aren't insects.

Petra: I know, I know. But they are also arthropods, and the methods we use for preservation for insects (at least for some of the insects) are the same that we use for spiders and other arachnids, but also myriapods (millipedes and centipedes).

We have over 45,000 described spider species. For some of the fauna, for example, in the soil we expect that 40% may yet to be described--

Emily: Wow.

Petra: --so we have a lot of unknowns there.

Emily: So there could be as many as 70-75,000 species of spiders.

Petra: Yes, easily, yes.

Emily: So like, 20 times the amount of mammals? I'm bad at math. I actually don't know what the ratio is.

Petra: Yeah.

Emily: So it seems to me that things like spiders, scorpions, they seem to elicit a really negative response from people. Why do you think that is?

Petra: Spiders do have many legs, and the legs I think in relationship to the body are a lot longer than an insect, so that may be also. They look a little more creepy. I think they move in unpredictable ways. But I think the main reason is people don't know enough about spiders because yes, all spiders are predators but the vast majority of spiders  have fangs that are far too small to ever penetrate even our skin. So the chance being bitten by a spider is really remote. Not impossible, but really remote.

Emily: Yeah.

When you're looking to learn more about spiders, what are some of the characters that you look at to differentiate species?

Petra: To differ-- How do I recognize 45,000 different spiders?

Emily: Yeah, exactly! That seems like a lot.

Petra: Right, right. A lot of spider families you can recognize just by the eye pattern, how the different-- how the eight eyes are distributed around the head.

Emily: But you mentioned that eyesight isn't a primary sense for a lot of these spiders, so...

Petra: For a lot of spiders it's vibration, good vibration. So spiders are really good at feeling vibration. So male spiders, for example, will court or have courtship movements in front or in the outskirts of the female's web. Now their copulatory organs are secondary organs. They are not directly connected to the gonads. All 45,000 spider species can be... you can tell them apart by differences in their copulatory organs. So the female basically has a duct system on her belly and sperm storage containers, where she actually keeps the sperm of the male alive. So for her, insemination does not mean fertilization. The eggs are fertilized when they are laid. The males have a very complicated organ and it just shows up here, for example, in one of the images on the screen.

Emily: Oh there it is.

Petra: That is at the end of their pedipalps, that are the shortened hand-like structures that males and females have in front of their legs.

Emily: They look like boxing gloves.

Petra: In males, exactly. In adult males, and males only have this complex organ develop once they are adults. So whenever you see a spider that looks like it's wearing boxing gloves, it's a male.

The survival of us and of our planet depends on that we have functioning forests and functioning fields and functioning habitats. So we want to know how many species we have, how they are distributed, changing climate, changing weather, shifting temperatures. These spider species with react in their range to these changing conditions. We can relate and use then these kind of relationship studies, for example, to also investigate the biogeography, how they are distributed and why certain species are distributed.

Emily: 'Cause that gives context for how other animals or creatures or plants or whatever have moved and migrated throughout the Earth changing climate in the last, you know, 600 million years.

Petra: Yeah, I did one of those studies that concerned African nursery web spiders that have some close relatives that basically went out of Africa and all the way to Southeast Asia, reaching Australia.

Emily: So if you could have any takeaway message for people who have... reservations about spiders. What would you say to them, or what are some of the comments you would give?

Petra: I think one of the most important perhaps things to think about is that although they have eight legs, they actually run out of oxygen very fast. They have their heart in their back and they have to stretch their legs by pumping blood into their, like into their legs because otherwise they can't stretch them.

Emily: Wow, mhm.

Petra: So actually, they can run very fast for a short time-- ten seconds. After that, they quickly run out of oxygen. So you can always outrun a spider.

Emily: (laughs)

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...it still has brains on it.