For small animals in the tropics, spiders and their arthropod cousins are responsible for “a surprising amount of death,” scientists recently discovered.
Researchers captured gruesome photos of the spiders’ hunting prowess in the Peruvian Amazon, revealing in a study that the arachnids regularly dine on frogs, fish, lizards and even small mammals.
Large tropical spiders are known to hunt vertebrates — animals with backbones — but this is the first study to collect observations of these predators in a region over time. The scientists also recorded the first evidence of a tarantula clutching one particularly unexpected victim: a young mouse opossum that was about the same size as the spider, a species in the Pamphobeteus genus.
Spiders and other arthropods that prey on vertebrates tend to have special adaptations to subdue their wriggly, muscular dinners, such as modified jaws, enlarged chelicerae — claws in front of their mouths — and powerful venom, the researchers wrote in the study.
Photos taken by the researchers documented multiple species of spiders and other arthropods (a group that includes spiders, insects and crustaceans) — such as a giant water bug and several centipede species — as they sank their mandibles deep into their prey. The study authors described 15 interactions captured in night surveys that took place during expeditions to southeastern Peru’s Madre de Dios region in 2008, 2012, 2016 and 2017, according to the study.
“In a single night survey, it’s fairly common to see between three and five predator-prey interactions,” lead study author Rudolf von May, a postdoctoral research fellow in the Department of Ecology and Evolutionary Biology at the University of Michigan (UM), said in an email.
“The most common interaction we see is spiders eating other invertebrate prey such as crickets and moths,” von May said. But vertebrate prey was also on the menu, the scientists reported. In one instance, a centipede was consuming a juvenile snake while it was still alive (the scientists humanely euthanized the snake after the centipede abandoned it).
These observations suggest that arthropods are “a major source of mortality” for small vertebrates, said study co-author Dan Rabosky, an associate professor of herpetology at UM and a curator at the UM’s Museum of Zoology.
Why does that matter? Scientists need a clear picture of how species interact to understand and protect fragile ecosystems that are increasingly at risk from human activity and climate change, Rabosky said.
“We’re trying to collect data as frantically as we can to at least get a snapshot of what’s going on now, so we can understand future impacts,” he said.