Scientists discover 18 new spider-hunting spiders from Madagascar

Morgan Erickson-Davis

6 years ago

Researchers have added 18 new species to the assassin spider family, upping the total number of known Eriauchenius and Madagascarchaea species to 26.
Assassin spiders, also known as pelican spiders, have special physical and behavioral adaptations that allow them to hunt other spiders.
The new species were discovered in Madagascar’s forests and through examination of previously collected museum specimens.
Madagascar is currently experiencing high levels of deforestation. Researchers say the loss of Madagascar’s forests is putting the new assassin spiders – as well as many other species – at risk of extinction.

With their long “necks” and sharp, fang-like mouthparts, assassin spiders hunt a strange prey – other spiders. Now, thanks to a study published recently in ZooKeys, there are 18 more known species in the world. Researchers think even more lie in wait in Madagascar’s unique, isolated forests, but are worried the country’s rampant deforestation will claim the spiders before they’re discovered.

Assassin spiders, also called pelican spiders, are native to Madagascar, South Africa and Australia. They’re nocturnal, hunting other spiders under the cover of darkness by following the silk lines of their unsuspecting prey. Once an assassin spider is close, it dispatches its victim by stabbing it with its fangs; its protracted “neck” keeps the hunter at a safe distance in case the other spider puts up a fight.

Known as “living fossils” because those that are alive today have scarcely changed from their forebears preserved in amber 50 million years ago, assassin spiders have been little studied since the first was discovered in Madagascar in the late 1800s.

Pelican spiders are beautiful and iconic Madagascan spiders. They have a bizarre appearance, with a long “neck” and chelicerae (“jaws”) that are used to prey on other spiders from a distance. This pelican spider (pictured above, top) is dangling its spider prey (bottom) upside-down using its chelicerae after capturing it. These spiders also occur in Australia and South Africa; however, the species with the longest “necks” occur in Madagascar. All of the pelican spiders that Wood described live only in Madagascar, an island whose tremendous biodiversity is currently threatened by widespread deforestation. The new species add to scientists’ understanding of that biodiversity, and will help Wood investigate how pelican spiders’ unusual traits have evolved and diversified over time. They also highlight the case for conserving what remains of Madagascar’s forests and the biodiversity they contain, she says. Photo by Nikolaj Scharff

Hannah Wood, curator of arachnids (spider and scorpions) and myriapods (millipedes and their ilk) at the Smithsonian National Museum of Natural History, set out to change this. She and her colleague Nikolaj Scharff focused on the Eriauchenius and Madagascarchaea genera, examining museum specimens as well as traveling to Madagascar to see what they could find in the island’s unique forests.

Wood and Scharff studied hundreds of spiders, which they grouped into 26 different species. Of these 26 species, 18 had never before been described – a discovery that wasn’t entirely unexpected.

“I wasn’t surprised,” Wood said. “We know very little about the total diversity of arachnids, and particularly in an area like Madagascar, I would say the majority of tiny arthropods are new species.” As field workers continue to collect more specimens in Madagascar, Woods believes more new assassin spiders are bound to come to light.

But Woods cautions that these undiscovered arthropods are at risk. Madagascar is currently experiencing widespread deforestation, fuelled by logging, mining and agricultural expansion. Satellite data from the University of Maryland show tree cover loss in Madagascar more than doubled between 2012 and 2013, and has remained high ever since. In total, the island lost more than 27,000 square kilometers (10,700 square miles) – or 16 percent – of its tree cover between 2001 and 2016.

Around 5 percent of Madagascar land area is officially protected. These places are less at risk of deforestation, but threats still persist. Protected areas cover most of Madagascar’s remaining intact forest landscapes – areas of native habitat that are undisturbed and connected enough to retain their original biodiversity levels. But these, too, are being whittled away, losing around 466 square kilometers (180 square miles) of old growth forest between 2001 and 2013.

Satellite data show Madagascar’s intact forest landscapes (IFLs) experienced significant degradation during the past decade. Several of the new species described in Wood and Scharff’s study were found in the IFLs shown.

In addition to these new assassin spiders, Madagascar’s forests are home to a unique array of plants and animals, many of which are found nowhere else in the world. From iconic lemurs to the world’s smallest chameleon, scientists and conservationists fear what will happen to Madagascar’s wildlife if its forests continue to be cleared at current rates.

Woods adds her own concerns on behalf of assassin spiders, saying their vulnerability to habitat change is leaving her worried about the future of these new species.

“For most of these species, if you lose the forests where they live, the species will go extinct,” Woods said. “These species are mostly found in pristine forests with very small distributions – for example, one species lives on a mountain top and nowhere else. These traits make these species susceptible to going extinct.”

Banner image: Zephyrarchaea barrettae from Stirling Range National Park, Western Australia. Photo courtesy of Michael G. Rix and Mark S. Harvey, Western Australia Museum via Wikimedia Commons (CC BY 3.0)

Citations:

Wood, H. M., & Scharff, N. (2018). A review of the Madagascan pelican spiders of the genera Eriauchenius O. Pickard-Cambridge, 1881 and Madagascarchaea gen. n.(Araneae, Archaeidae). ZooKeys, 727, 1.
Hansen, M. C., P. V. Potapov, R. Moore, M. Hancher, S. A. Turubanova, A. Tyukavina, D. Thau, S. V. Stehman, S. J. Goetz, T. R. Loveland, A. Kommareddy, A. Egorov, L. Chini, C. O. Justice, and J. R. G. Townshend. 2013. “High-Resolution Global Maps of 21st-Century Forest Cover Change.” Science 342 (15 November): 850–53. Data available on-line from:http://earthenginepartners.appspot.com/science-2013-global-forest. Accessed through Global Forest Watch on February 6, 2018. www.globalforestwatch.org

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