Spiders get a bad rap. Especially around Halloween, when spiders and other creepy crawlies are seen as a spine-chilling symbol of spookiness. Arachnaphobia, or the fear of spiders, is quite common, afflicting 3-15 percent of people.
But Hannah Wood has nothing but affection for these shy creatures. As the curator of Arachnida and Myriapodia at the Smithsonian National Museum of Natural History, Wood gets up-close and personal with spiders out in the wild and in the lab.
While thinking about a spider’s fanged jaws may give some people the heebie-jeebies, for Wood, it’s a source of endless fascination. “Being educated about them helped me be less afraid,” she said.
Wood has traveled to Madagascar, Chile and South Africa in search of spiders to learn more about their traits, behaviors and geographic range. But she never envisioned herself as a globe-trotting arachnologist in her younger days. In college, she studied literature. But she developed a passion for science after taking an insect taxonomy class “just for fun.” Her winding career path eventually led her to the forests of Madagascar, where she first fell in love with spiders.Wood’s research investigates the evolution of spider morphology – how different species developed the traits they have today. She uses the fossil record to inform her observations of present-day spiders. This helps her determine when and where certain traits emerged throughout evolutionary history. Her current work focuses on a specific group of spiders whose jaws have evolved to chomp down on prey in the blink of an eye. Wood gave them their common name – the trap-jaw spiders – because of this mechanism.
In this month’s installment of Meet a SI-entist, Smithsonian Voices chatted with Wood to learn how her work is untangling the web of arachnid evolution.
Many people are terrified of spiders. But are these animals actually dangerous, or just misunderstood?
There are a very small number of spiders that are aggressive and highly venomous. But because of them, all spiders get a bad rap. I think the only way for people to let go of their misconceptions about spiders is to learn about them.
When I first started studying insect taxonomy, I learned about the mouthparts and stingers of insects – all the ways that insects can harm you. Being educated about that actually helped me be less afraid, because I knew which species I could safely pick up and which I couldn’t. It’s the same with spiders. Almost all spiders do have venom for killing their prey, but the vast majority of their venoms are harmless to humans, and they are so shy that they’re never going to harm you.
My motivation for studying spiders is understanding their diversity. There are thousands of species of spiders, and half of them haven’t even been documented or seen yet. Spiders are also important to their local ecosystems. They play a crucial role as predators of arthropods, soil vertebrates and small flying insects. If you remove spiders from the ecosystem, there’s going to be downstream effects. We definitely don’t want to lose them.
How do you use the fossil record to inform your research?
A lot of biologists who study the fossil record are looking only at fossils, in the same way that those who study living groups are only looking at living organisms. But there is something that happens when you start to look at both together – it gives you a whole different perspective.
In the last five to ten years, more biologists have started to look at living groups in combination with their fossil members. Of course, my work on spider feeding behavior and jaw mechanics relies on living specimens. But in terms of biogeography (the study of an animal’s geographic distribution) and studying evolutionary relationships, I really look at both the fossil record and living spiders. This allows you to discover traits that arise in the fossil record but do not appear in any of the living groups. You can look back in time and see how groups that seem so distinct from each other today once shared traits 100 million years ago. This helps me piece together how these traits evolved, and how different species diversified.
Your research mostly focuses on one superfamily of spiders: the palpimanoids. Why did you choose to study them?
The palpimanoids are an incredibly interesting group, especially for people studying the evolution of spiders. They have an extensive fossil record that I would argue is one of the best among spiders. It goes back 170 million years. Palpimanoid fossils appear in amber from the Dominican Republic, the Baltics, India, and Burma, as well as in traditional fossils from China and Brazil.
Their fossil record suggests that at one time, the palpimanoids were much more abundant and widespread. But as more modern spiders evolved, palpimanoids became restricted to smaller geographic areas and ecological niches. Over time, this caused many different, highly-specialized palpimanoid species to evolve, which is why we have the diverse group we see today.
Many of them specialize in preying on other spiders, and they have evolved behaviors and morphologies to help them attack their prey. In particular, they’ve evolved some really interesting mouthparts to keep themselves safe when targeting another spider. The most exciting thing I’ve ever discovered was the trap-jaw spiders. They have unusual morphologies, but no one had ever looked at why they have these weird long necks and jaws.
I began recording their feeding behavior with a high-speed video camera, and found that some species had evolved a mechanism like a catapult to produce these extremely fast jaw movements – the fastest movements among arachnids. So, the palpimanoids are a really interesting group for studying how trait evolution happens over time and how modern groups evolve.
How do you locate the strange spiders that you study?
To find these spiders, you have to go to really healthy forests. You aren’t going to find them in degraded habitats. But the type of collection methods I use depend on where I am.
In New Zealand and Chile, you have a lot of species that live on the ground, so I’ll spend the days sifting through leaf litter. I take a special sifter and fill it with litter, then I shake it to allow the soil and small arthropods to fall to the bottom. After that, I spread this concentrated leaf litter out on a sheet and examine it for spiders. But at night in Madagascar, you can go out and observe the spiders actively hunting on the trees and even collect them by hand. In Australia, spiders hide in mats of thick grasses, so I place a tray beneath the mat and shake it to dislodge and collect them. There are a variety of different methods – once you know where to find spiders, you know which method you should use to collect them.
I preserve the specimens I collect in ethanol, then gather data about them in the lab. I will take a leg or two, and then extract and sequence its DNA. I’ll take images of the specimens to perform morphometric analysis, which is an analysis of their shape that allows me to compare the structure of different traits. I also do CT scanning, which is equivalent to an MRI for humans, to look at the internal musculature of a spider’s mouthparts. Right now, I’m working with collaborators to model those muscles. That will allow us to understand how they function, and compare among all these different species to get an idea of how they are using their jaws. One specimen goes through a lot!
In my home state of Maryland, there are several local species, including daddy long-legs and wolf spiders, that I collect and study in the lab while it is still alive. I record this species with a high-speed video camera so that I can see the mechanics of their mouthparts in action. I analyze those videos in order to quantify the movement and compare it to how the mouthparts of other species function.
Why is it important to understand and document the evolution of spiders?
Arachnology is falling behind compared to what’s known about a lot of other animal groups. Vertebrates, for example, have been studied much more extensively than arachnids. It’s only been in the last five or six years that arachnologists have been able to make progress toward constructing a phylogeny of life for all spiders thanks to new molecular research methods.
Establishing that phylogeny enables you to ask much bigger questions about functional morphology, macroevolution, and how traits relate to diversification. Arachnids are so old, they go back over 400 million years. They’re like living fossils. I think there are interesting new discoveries to be made by studying their evolutionary history, especially because they’ve retained some traits over millions and millions of years.
This research also has implications outside of the field of biology. Spiders are like these little hydraulic pumps – they have high internal pressure and they use hydraulics in a lot of their movements. Understanding those mechanisms can provide insight for the field of robotics, or other applied areas. I think arachnology is going in a really good direction right now, and there’s going to be a lot more we can learn from arachnids now that we’re finally able to ask those bigger questions.
This conversation has been edited for length and clarity.
Meet a SI-entist: The Smithsonian is so much more than its world-renowned exhibits and artifacts. It is a hub of scientific exploration for hundreds of researchers from around the world. Once a month, we’ll introduce you to a Smithsonian Institution scientist (or SI-entist) and the fascinating work they do behind the scenes at the National Museum of Natural History.
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