Madagascar's Ancient 'Pelican Spiders' Are As Striking As They Are Strange
Traipsing through the thick brush of the Madagascan jungle in search of exotic spider species, all the while plucking bloodthirsty land leeches from your legs and eyeing the sky for signs of cyclones, might not be an activity high on your personal bucket list. For veteran arachnologist and Smithsonian researcher Hannah Wood, though, the natural wonderland of Madagascar has become a sort of home away from home.
In a recently published research paper in the academic journal ZooKeys, Wood and her co-author Nikolaj Scharff shed light on the taxonomy of a group of particularly distinctive-looking Madagascan spiders. Formally known as Archaeids, the creatures are perhaps best described by their common name: “pelican spiders.” Each spider in this group boasts an extended, arching carapace and two extra-long mouthparts (called chelicerae), creating the illusion of a “neck” and “beak.” The resemblance to pelicans is uncanny.
The unusual appearance of Archaeid spiders, like most traits selected for in the course of Darwinian evolution, has a very practical purpose: it makes spider-vs.-spider hunting, the specialty of the pelican spider, considerably easier. Most spiders aren’t picky eaters—they’ll feed on whatever they manage to catch in their webs. If that means a little cannibalism now and then, so be it. Archaeids, for their part, eat nothing but spiders (though they try to avoid making meals of their own species). Flies aren’t even on the menu.
Having stalked or lured out a target spider, an Archaeid will strike swiftly, thrusting its two chelicerae downward to impale the prey, then holding it at a safe distance (out of range of venom or web attacks) until dead. Archaeids are by no means the only spider-killer spiders out there—the “pirate spiders” of the widespread Mimetidae family, for instance, are well known for tugging on the webs of other spiders to coax them down, then feasting on them. The bizarre “pelican” morphology of Archaeidae is what sets them apart.
Another defining feature of the Archaeid family is hinted at by their Latin name: these are old spiders—very old spiders. “What my research has shown,” says Wood, a curator at the National Museum of Natural History, “is that these spiders have likely been on Madagascar since Pangaean times, 180 million years ago.” In other words, pelican spiders were probably on what we now know as Madagascar before it was even an island, and they almost certainly predated the birds after which humans named them.
Amusingly, scientists first discovered pelican spiders in the fossil record—preserved in Baltic amber dating to the Eocene Epoch—and only subsequently found the same family, alive and well, in modern-day Madagascar. “It was quite amazing,” says Wood, “to know this spider from a fossil that’s 50 million years old and then find it living in Madagascar.” Additional pelican spider evidence has since turned up in 95-million-year-old amber, and seemingly in 165-million-year-old compression fossils. That they were around for the breakup of the continents is entirely plausible.
Across the various Archaeidae species of Madagascar, Wood has observed a staggering degree of physical diversity. Curiously, this is not the case with related families of South Africa and Australia—those spiders all tend to be fairly homogeneous. Wood explains this by pointing to the geological history of the respective regions. “Madagascar had many more ancient geological and climatic events,” she says, “whereas in South Africa and Australia, it was very recently that you had some major climatic events, such as the aridification of Australia and the uplift of mountains in South Africa.” The species of Madagascar have had ample time to adapt in their own ways to the niches created by macroscopic environmental change, then, while those of Australia and South Africa were only recently agitated, and thus still appear relatively uniform.
The diversity of Madagascan pelican spiders was the main impetus for the ZooKeys paper, which provides detailed descriptions of 26 distinct species, 18 identified for the first time, in two separate pelican spider genera: Eriauchenius and Madagascarchaea. Largely the result of a thorough analytic survey of specimens from various museums, Wood’s paper also draws on several specimens she personally collected. Sorting the spiders with the aid of a powerful electron microscope, the researcher relied on such distinguishing markers as genital morphology and carapace shape to make her classifications.
The Madagascarchaea genus makes its formal debut in this paper. When Wood first studied those spiders, back when she was pursuing her master’s degree in the 2000s, the consensus view was they should be lumped in with the members of Eriauchenius. Over the course of her work, Wood came to realize that they were sufficiently dissimilar to merit a genus all their own.
Even if you’re not a taxonomy junkie, the mere fact that a type of spider whose heritage extends across dozens of millions of years is surprising scientists to this day is pretty remarkable. One of the main reasons Wood loves her work so much is the astonishing frequency of discovery—as far as animal species go, we still have so much to learn.
“The coolest part of the study,” says Wood, is its capacity to stoke the imagination, reminding us that “there are so many species we don’t know about. And in Madagascar, this is common, for arachnologists to be finding and describing new species.” That, she says, is very exciting. “There’s so much that we don’t know about these spiders.”
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