Daddy Longlegs Seem to Hunt Frogs in South America, Revealing the Gangly Arachnids as Overlooked Predators

A new study suggests that harvestmen actively attack the slippery amphibians, rather than just scavenging them. The findings hint that the spineless creatures have a more complex relationship with vertebrates than previously thought

Sarah Kuta | Daily Correspondent

May 27, 2026 9:00 a.m.

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Lizardo Proaño was leading a group of travelers on an evening hike through the towering trees and lush foliage of Ecuador’s cloud forest in February 2020 when he spotted something that stopped him in his tracks: a daddy longlegs, also known as a harvestman, chowing down on a live frog of roughly similar body size. He called over his colleague, Juan Carlos Narváez, who snapped a few photos of the macabre scene.

Proaño works as a naturalist guide at Mashpi Lodge, an eco-hotel located within the 7,900-acre Mashpi-Tayra Reserve, so he’s intimately familiar with the diverse creatures that wander the forest’s misty hills. And though he had never seen a harvestman eating a frog before, he wasn’t necessarily surprised, given that harvestmen are omnivores known to consume just about anything they can get their gangly legs on. He’d previously seen the spindly arachnids eating worms, caterpillars and, once, the tail of a scorpion.

“I didn’t know this was something special,” Proaño tells Smithsonian magazine. “I thought it was normal because frogs are good prey for everybody. They don’t have any scales or hard bones. They are like gummy bears in the forest.”

But when Proaño later mentioned the encounter to Esteban Calvache, a biologist at Mashpi Lodge, Calvache was immediately intrigued. Proaño, it turns out, had witnessed one of just a handful of known instances of harvestmen preying on adult frogs, according to a study published in April in the journal Ecology and Evolution.

The list, compiled by Calvache, Proaño, Narváez and an international team of co-authors, is short, with just ten documented cases globally, all occurring in South America. These observations involved predators about the same size as their prey. And in several sightings, the frog was still alive, which suggests harvestmen—scientifically, members of an arachnid group called Opiliones—may be actively hunting them.

That’s a fascinating, but not entirely unexpected, finding for Shahan Derkarabetian, the curator of invertebrate zoology at the San Diego Natural History Museum who was not involved with the new study.

“There is so much we do not know about Opiliones,” Derkarabetian tells Smithsonian. “They are such a diverse and versatile group that it never ceases to amaze me when I find out something new about them.”

Harvestmen may look like spiders at first glance, but the estimated 6,660 described species form a distinct group of arachnids more closely related to mites, ticks and scorpions. Though they have eight legs, their simple, oval-shaped bodies lack the defined “waist” of spiders, and most species have just two eyes instead of multiple pairs. They also lack venomous fangs and silk glands, so instead of spinning webs to catch unsuspecting prey, they wander around in search of whatever tasty morsels they can scavenge. Additionally, harvestmen eat solid food, rather than liquefying and slurping up other creatures like spiders do.

“They are more specialized for foraging,” Calvache, the lead author of the new paper, tells Smithsonian. “They are considered generalists. They are normally going to be eating the residuals of different materials such as fruit, other arthropods. They are on the move constantly, walking and wandering in the forest to get resources.”

That’s why Calvache was so surprised when Proaño showed him photos of his February 2020 encounter. When he scoured the scientific literature and asked around to colleagues, he learned of just a handful of other documented field observations from Ecuador, Brazil, Colombia and Venezuela.

One of the sightings came from iNaturalist, a citizen science platform that allows anyone with a camera to take and upload photos of wildlife, including unknown species. For scientists studying under-researched creatures like harvestmen, platforms like iNaturalist can be invaluable, says Derkarabetian.

The paper “shows how simple natural history observations can lead to important, or even new, findings,” he adds. “Just being out in nature and taking a picture of some behavior can become data and lead to a scientific publication.”

The gruesome field observations not only deepen scientists’ knowledge of an under-studied group, but they may also reshape their understanding of the broader tropical forest food web. Scientists usually think of arthropods—the massive group of spineless critters, including insects, crustaceans and arachnids, that makes up roughly three-quarters of all animals on the planet—as prey for backbone-bearing vertebrates. However, they’re starting to realize this view is probably too simple.

That may be especially true in the tropics, where harvestmen tend to be larger and hardier than those found in other parts of the world. “These are big harvestmen that are looking for important resources they need to sustain a big body,” says Calvache. “In the tropics, those behaviors that are probably not very easy to imagine at other latitudes are real. They’re really happening here.”

But why are harvestmen going after frogs specifically? The answer is simple: “Because they can,” says Calvache. “If they can capture one, why not eat one?”

Frogs are “super, super abundant” in tropical forests, Calvache says, and he suspects harvestmen are simply taking advantage of this bounty. Some species of harvestmen have strong, spiny mouthparts, which may be ideal for catching and holding onto slippery frogs. They might also be ambushing frogs that are injured, slow or “sleepy,” says Calvache.

The behavior is probably even more common than researchers realize. Harvestmen are nocturnal and tend to be most active between midnight and 3 a.m., when few people are around to observe them, says Calvache. Additionally, compared to other more easily observable arthropods, relatively little scientific attention has been given to harvestmen, so researchers are still making basic discoveries about their diet and behavior.

Future studies might explore how harvestmen are capturing and subduing adult frogs, as well as how often they go after the soft, slimy amphibians. Researchers are also curious to know whether sexual dimorphism—physical differences between males and females—plays a role in their predatory behavior. In many species of harvestmen, females are larger than males. However, males sometimes have spines on their legs or enlarged mouthparts that help them compete with other males and guard their territories. Scientists wonder if these sex-specific characteristics help the arachnids nab frogs.

“There are lots of hidden mysteries in the mist,” says Calvache.

Sarah Kuta | Read More

Sarah Kuta is a writer and editor based in Longmont, Colorado. She covers history, science, travel, food and beverage, sustainability, economics and other topics.