Spiders are scary, even in the best of times, but new photos taken in the Amazon rainforest give these predatory creatures an even more daunting picture: they graze animals of unusual sizes.
New research published today in Amphibian and Reptile Conservation highlights more than a dozen rare predator-prey interactions involving arthropods (predators) and small vertebrates (the victims). Arthropods are a group of creatures including insects, crustaceans and arachnids, the latter consisting of spiders, scorpions, mites and ticks.
The new study, led by evolutionist biologist Daniel Rabosky of the University of Michigan, offers abominable photographic evidence of arthropods – mostly spiders – feeding on a surprising number of over-excited animals, a list including frogs, tadpoles, lizards, snakes and unprecedented case, an unfortunate opossum.
About once or twice a year, Robosky and his colleagues travel to the Los Amigos Biological Station in the remote Madre de Dios region of southeastern Peru. Here, in the Amazon rainforest of the lowlands near the Andes hills, scientists collect ecological data on reptiles and amphibians. They have been doing so for more than a decade, and over the years the group has been able to collect a surprising amount of visual evidence of terrifying, often unexpected, interactions between arthropods and small vertebrates. In fact, Robosky's team decided to publish an article on the subject.
"It's a source of underestimated mortality in vertebrates," Rabosky said in a press release. "A surprising amount of small vertebrate deaths in the Amazon is probably due to arthropods such as large spiders and centipedes."
The observations documented in the paper were mostly done at night, when arthropods are the most active. The researchers cautiously walked through the dark forests, guided by flashlights and camera-equipped.
Among the most shocking observations, there was spider-opossum interaction. Michael Grundler, a PhD candidate at the University of Michigan and co-author of the study, was alerted to the scene when he heard stirring sounds from a pile of leaves .
"We looked at it and we saw a great tarantula at the top of an opossum," said Grundler in the press release. "The possum had already been gripped by the tarantula and was still struggling weakly at that time, but after about 30 seconds, he stopped kicking."
The tarantula was as big as a plate and the possum was about the size of a softball. It is considered the first visual documentation of an opossum attacked by a large mygalomorphic spider, a group comprising tarantulas.
Predatory arthropods have special body parts, such as modified jaws, a large beak and big fangs to capture the victims. They also use venom to immobilize their prey.
Other observations have involved Ctenidae spiders – spiders say "sit down and wait". As their name indicates, these arachnids are waiting for their prey to come to them. By using special hairs that detect vibrations, spiders can detect the presence of a possible meal nearby. Ctenidae spiders used their main eyes to discern an object, and its secondary eyes were used to detect motion.
But not all spiders. Large centipedes have been seen eating a live snake-eating snake from Catesby and a dead coral snake whose head had been torn off by the insect.
"Coral snakes are very dangerous and can kill humans," said Joanna Larson, PhD candidate at the University of Michigan and co-author of the study. "To see one who was taken by an arthropod was very surprising. These centipedes are terrifying animals, actually.[Amphibian & Reptile Conservation]