Daddy longlegs, also called harvestmen, have been documented catching and consuming living frogs larger than themselves in South American rainforests. All without the use of venom.

Previous literature has noted occasional interactions between daddy longlegs and frogs, but accounts have been largely anecdotal. Now, researchers report novel field observations of the arachnids preying on anurans (frogs).

“It is genuinely exciting to encounter observations that challenge the simplified narratives we learn from textbooks,” Luís Fernando García at the University of the Republic in Uruguay tells Refractor. “Finding a seemingly harmless, non-venomous harvestman overpowering a frog is one of those moments that make you stop and rethink what you thought you knew.”

Generally, invertebrates (animals without a backbone) are viewed as prey of other invertebrates or predators of other invertebrates. Because of their smaller body sizes than vertebrates, arthropods are often portrayed as prey of vertebrates.

But now, a study published in Ecology and Evolution records the predation of frogs by a family of harvestmen (Opiliones), suggesting that such ecological interactions may be more widespread than previously thought.

“These observations remind us that biology is dynamic and that many interactions in tropical ecosystems remain undocumented. Rather than overturning established knowledge, they enrich our understanding of how complex and surprising nature can be,” García says.

It is important to note that the researchers did not physically collect specimens during these field encounters; all of their primary evidence relies on photographic records. García and his colleagues reviewed four specific predation events observed at multiple locations across the tropics by species in the family Cranaidae of the order Opiliones.

García says that harvestmen are generally viewed as slow, fragile, and defenseless animals. Frogs, on the other hand, are larger, faster, and highly mobile.

“Watching an animal that appears so vulnerable successfully exploit prey that seems far more capable of escaping was remarkable,” he says. “What surprised us most was seeing harvestmen feeding on relatively large frogs and, in some cases, apparently keeping them immobilized while they were still alive.”

Given the absence of venom, the researchers propose that these arachnids likely use strong raptorial pedipalps (claw-like appendages). These pedipalps are “armed with prominent spines and function as an effective grasping device that allows them to firmly restrain the frog while feeding,” García says.

The researchers suspect that harvestmen may target strategic regions of the amphibian's body, thereby significantly restricting the frog's movements. Such similar immobilization of the prey is observed in predatory beetles of the genus Epomis.

The biologist also hypothesizes about the prey’s conditions. Some frogs may have been sleeping, weakened, injured, or otherwise compromised before being captured. Since these are speculations, “we cannot determine whether the frogs failed to resist because they were physically restrained, because they were already weakened, or because of a combination of factors,” García told us.

More interestingly, one of the frog species involved in this interaction is considered threatened. “Understanding these interactions may therefore have implications beyond basic natural history, potentially contributing to our understanding of predator-prey dynamics and informing conservation efforts for both predators and prey,” García concludes.

The study has been published in Ecology and Evolution.

Fact-checked by Mike McRae