GO AHEAD: THANK A SPIDER today for all their hard work that helps make life on earth possible. Spider expert Rod Crawford of the Burke Museum in Seattle explains spiders’ critical role–and things like why are their webs so many different shapes, and how they hunt, and more.
The back story: In my increasingly obsessed pursuit of moths the last couple of summers, I’ve gone out into the darkness more than I used to, camera and flashlight in hand. In another podcast and blog post, I’ll tell you about some of the 180 moth species I’ve photographed and ID’d so far-yes, 180, and counting, fueled simply by curiosity-but this story is about another group of creatures I’ve encountered on my after-dark adventures and likewise become fascinated with: spiders. The spider in the photo above, a female Larinioides sericatus, spent the summer making a web above my back door, and was just one who caught my eye in the darkness.
The more spider species I saw those evenings (some of which like the one above, a male Agelenopsis, were also looking for moths), the more I started reading, looking to answer my growing list of questions. Pretty quickly I came upon a series of articles debunking common myths about spiders from the Burke Museum, specifically from Rod Crawford, who curates the Arachnid collection there.
He joined me on the December 26, 2016 edition of my public-radio show and podcast. Read along as you listen using the player below, or at this link. And enter in the comments at the very bottom of the page to win a book about spiders that Rod recommends we start with to learn even more.
a spider q&a with burke museum’s rod crawford
Q. For people who do not know the Burke Museum, can you give us a little background?
A. It was founded in 1885, by a group of students and alumni in the very early days of the University of Washington. Before too long, by 1899, the state declared it the official natural history museum. Since then it has been housed in various different buildings on the University of Washington campus, each of which in time deteriorated and was demolished. Right now we’re in the process of building our newest building for the 21st century.
Q. I read that Burke houses some 16 million objects in its collections, but how many are spiders?
A. About 170,000.
Q. Oh my goodness. And you also curate other organisms?
A. I oversee the centipedes and millipedes, isopods, non-spider Arachnids (which I am very interested in), and a few other small collections.
Q. I’m millipede-crazy, so that will be another conversation, Rod. [Laughter.] [Above, the giant millipede, genus Narceus, proliferates in Margaret’s garden.]
A. I know a guy who would be much better for you to talk to about millipedes than me.
Q. Well, I’m going to get the info from you on email, because that is a fascinating subject. But back to spiders: I love your spider myth pages on the Burke website as I mentioned in the introduction. You kick them off with a great quotation, which really made me laugh.
It’s a quote from someone whose pen name was John Billings, a 19th century writer.
A. He came up with that pen name to let people know he was only joshing.
Q. [Laughter.] He said:
A. That is a quote that is subject to a quotation myth. It’s usually attributed in other forms to Mark Twain, who never said it.
Q. Henry Wheeler Shaw, who is Josh Billings when he’s not joshing, has a triathlon named for him that’s been run for 40 years in my area–a funny coincidence.
A. Well that’s great; I am happy to hear that.
Q. So we want to know not the myths, or falsehoods; we want to know the true stories. Even some very smart and otherwise stable people I know are terrified of spiders, which always surprises me.
I thought you could give us some perspective or context on how much we actually depend on spiders in the bigger order of things? What’s their role?
A. Spiders are the leading predators on insects. There is a famous study, done in a forest in Tennessee, where in a given tract all the insects were labeled with radio-isotope tracers, so you could track what happens to the insect flesh. In the course of a year, 44 percent of it ended up in spiders.
Q. Good for them. They keep things in check; we have them to thank.
A. You’ve seen footage of a plague of locusts. That’s what happens when one insect species gets out of check Imagine tens of thousands of species freed from the limitation that spider predation put on them. Then imagine human civilization trying in vain to survive.
Q. Critically important, and we should thank them, not be terrified by them. How many species is it estimated that there are in the U.S. or the world, and are more being ID’d all the time?
A. I don’t know off hand the total for the U.S. But in the world there are about 44,000 or 46,000 named, and counting the ones that are in collections that are known to scientists but not named yet, it has to be at least 50,000.
And that could be as little as 10 percent of what’s really out there.
Q. Let’s go through a few of the spider myths you tackled, starting with the mistaken impression most people seem to have that spiders are insects. [Read Rod’s “spiders are insects” myth page on the Burke website.]
A. I don’t know that it’s most people; about half the people I talk to did learn in school that spiders are not insects, but it astonishes me that the rest of them didn’t manage to pick that up. Maybe they had a clueless science teacher, or maybe they didn’t listen.
But I mean journalists are particularly bad about this. I couldn’t count the number of times I have had an interview with some journalist and then they publish something like, “Spiders are important they eat so many other insects.”
Q. The “other” being the misplaced word in that sentence.
A. Other than what?
Q. Both insects and spiders are arthropods, but they are distinct.
A. Yes, they are separate classes of arthropods. Several groups of crustaceans are also among the classes of arthropods. Centipedes are a class; millipedes are a class. Insects are the biggest class; Arachnids are the second biggest class, and they contain 11 orders, one of which is spiders.
Q. So they are Arachnids. And they have a different number of body parts, a different number of eyes–there are physiological distinctions from insects.
A. No wings, no antennae. Spider in particular have visibly unsegmented bodies, though that is not true of all Arachnids. Just look at a scorpion. [Above, spider versus insect illustration from the Burke website.]
Q. Talking about Arachnids brings up another myth, where people mistake some other ones for spiders–like the familiar arachnid that people may variously call harvestmen or daddy long legs. People think those are spiders.
A. Yes, and they have eight legs–but so do scorpions, and nobody would call a scorpion a spider. [Rod’s myth about “arachnid just means spider” on the Burke website.]
A. Since a harvestman doesn’t have big claws or a tail, they think it’s a spider. But actually scorpions have more in common with spiders that harvestmen do. They have venom, like spiders, and have a similar respiratory system. The immediate ancestors of spiders had a similiar mating procedure as scorpions do, although spiders themselves have really gone out on a limb as far as weird sex. [Rod’s daddy long leg’s myth on the Burke website.]
Q. [Laughter.] We’re going to get to that in a minute.
A. But harvestmen [above, probably Leiobunum vittatumon, on Margaret’s barn door] are unique in all the Arachnids. They have a direct copulation, using an organ that is actually called a penis.
Q. That’s very different. Let’s talk about webs first. Do all spiders make them?
A. About half are in groups that forage for prey by means of webs. The others are known as hunting spiders, and hunt for their prey or sit and wait for their prey, without benefit of a web.
That doesn’t mean they don’t make silk, but many silk structures have all kinds of purposes other than prey capture. Only if it’s used for prey capture is it a web. [All about the types of webs, from Rod’s spider myth pages on the Burke website.]
Q. I was fascinated, as I mentioned in the introduction, going out at night looking for moths to photograph, and seeing different spiders than I was accustomed to seeing in my house, or in the garden in the daytime. And seeing different shapes of webs than I was familiar with–especially ones that were a funnel or tunnel shape. Do males and females both make webs?
A. Adult males stop making webs the minute they become sexually mature. However, until they are sexually mature, both sexes behave the same. Adult males have nothing on their little minds than cruising for chicks.
Q. [Laughter.] Well I am glad that’s the universal order.
So for instance these funnel-weaving spiders–is that something they create to capture insects? [Below, a female grass spider, Agelenopsis sp., on its funnel web at night at Margaret’s.]
A. A funnel web is a prey-capture web. Unlike an orb web, for example, it has no sticky silk whatsoever; it functions by being made of very thick multiple-layered silk that an insect’s foot and leg can sink into.
Insects only have two claws, never more than two at the end of each leg. They’re pretty much stiff–fixed in position. They can latch onto things, but web-making spiders have three claws and one is opposable.
We primates are so proud of our opposable thumbs, but spiders did it first.
Q. Opossums have opposable thumbs on their hind feet, if I am not mistaken–another creature with it.
A. A funnel-making spider can latch onto individual threads and skim right over the top of the web, so they are like someone on skis, chasing someone who is floundering around in knee-deep snow.
Q. What other uses for silk are there? You said all spiders make silk.
A. The two most universal uses for silk are the drag line and the egg sac.
Q. Drag line!
A. Not to be confused with a drag net.
Q. So for when they descend quickly?
A. Yes, but even when they are not descending, all spiders leave a thread behind them, from tarantulas on down to the tiniest micro-spiders, wherever they go. When you are a 2mm-long spider on a 1-foot-high plant, you’re basically a mountain climber.
Q. [Laughter.] You’re right.
A. So it helps to be belayed. And also spider silk also contains pheromones, which means something to the opposite sex of that spider.
Q. So there is an attractant, a lure, to the silk?
A. Or the other way around.
Q. Or a repellent.
A. It tells a male spider, “Oh that’s a male; I don’t want to chase him,” or that, “That female has been mated and is not going to mate with me.”
Q. The spiders that don’t make webs that you said hunt: For instance, in the summer in the garden sometimes, I will see inside flowers what I refer to as the generic term crab spiders. They may be very bright yellow and small–and right in the center of flowers. I’ve never seen them on a web. [Above, probably Misumena vatia, in an opium poppy in the garden.]
A. Those are examples of a sit-and-wait strategy in hunting spiders. There are several different species in the crab spider family that are known as flower spiders. Many of them can actually change their color in an attempt to match the color of the flower.
Q. So they have almost like a crypsis–they can camouflage themselves?
A. Yes, if you see one that’s yellow, it either is or has recently been on a yellow flower.
Q. And that’s where I see them: in centers of poppies and so forth that have prominent yellow centers. Fascinating. [More about flower crab spiders on BugGuide.net.]
A. One of the great arachnologists of all time did a very simple little experiment. He went to a field of yellow flowers, and put yellow pebbles on a number of them, and black pebbles on an equal number of them–and counted which ones were most visited by potential prey.
Unsurprisingly, the ones that had yellow pebbles were the ones that fooled the prey into visiting them.
Q. So those crab spiders that I mentioned, in the middle of the flower, they are there waiting for the insect to come in–who’s also attracted to that flower–and they’ll grab them up. That’s one of their hunting tactics?
A. Yes, and beekeepers don’t particularly like flower crab spiders, but they actually don’t take out very many honeybees. Honeybees have worse problems these days.
Q. Yes. Let’s go in the house for a minute, and in my cellar I have this spider [above, Achaearanea (Parasteatoda) tepidariorum with five of her six her egg sacs] that I have been saying hello to every morning when I go down to check things, and I think it’s a female because there are all these egg sacs. So she…is that right to say “she” if there are egg sacs? [Laughter.]
A. Yes. I hate it when people call all spiders “he” regardless of sex. [Read Rod’s “all spiders are male”myth on the Burke website.]
Q. Why do you think people do that? That was one of your myths also.
A. I think because they think a spider is too creepy to be a girl. [Laughter.] [Illustration from Burke website below shows enlarged “palps” that distinguish male from female spiders.]
Q. I think this one is a she because she keeps making more of these brown, papery-covered and pointed-tipped egg sacs. She is very busy down there, and has been there for months, and seems focused on her job. What’s going on? What is the reproductive life–is there maternal care in spiders?
A. There is maternal care in some spiders; in others there is very little. That particular species you have in your basement is known as the American house spider; it’s in the cobweb weaver family. They keep their egg sacs more or less near the web, so it’s somewhat protected in that way. But other than that they don’t do much.
Q. [Laughter.] No, she doesn’t do much; she’s just there making these egg sacs.
A. And that is an example of a cobweb which has a very different prey-capture strategy than other types of webs. It has some sticky threads, which are only on the periphery. In your basement, the sticky threads would be the ones contacting the walls on either side, or the floor beneath–and not the ones in the main part of the web. And they are there to capture crawling prey that are crawling along the substrate.
Q. When you say “cobweb,” this American spider’s web looks messier–it’s not the orb with a geometric pattern.
A. It appears messier at first glance because all you see is the seemingly random central part, but if you look more closely, you’ll see the numerous straight sticky threads at the periphery, all going in one direction.
Q. I hope she won’t mind if I go down there later, when I get home, and have a closer look now that you have advised me. [Laughter.]
Another myth you explore is how in fall people think outdoor spiders want to come inside for the winter. Is that a true thing?
A. Not in any way, shape or form. They’re sort of putting themselves into the spider’s place there–thinking, “If I were out in the cold, I’d want to come in.”
A. But they’re mammals; they’re homeothermic. They’re subject to hypothermia if they get stuck out in the cold. Spiders are not homeothermic; spiders don’t particularly care whether they’re warm or cold. And they are definitely not attracted to warmth–there is experimental proof of that. [Rod’s myth page about “spiders comeindoors in fall.”]
Q. So some are adapted to our indoor environments–like the American house spider?
A. Yes, there are house spider species, most of which are not native to the areas where they are found by homeowners.
A. That particular species, for example, is practically never found far away from a building.
Q. Interesting. Are spiders solitary or are they ever social? You mentioned some do provide maternal care.
A. Of course they have to get together for mating. But there are a few species of social spiders. Most of those species are tropical. I have never directly encountered one of those species personally. Those species come in for way more than their share of study, because they are the only species that interest sociobiologists.
Q. If people want to learn more about spiders: Are there field guides to spiders or online references that you can recommend to lay people?
A. The place to start is a book in the Golden Nature Guide Series, called “Spiders and Their Kin,” by Herbert Levi–that is, if you want an actual paper book. There are a couple of recently published North American field guides–they’re pretty expensive.
And then of course there is my website–and then my other website, The Spider Collector’s Journal. [Below, a shamrock orbweaver in Margaret’s garden.]
more from rod crawford
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