John Uribe was hiking through the Colombian Andes when he spotted a tiny, eight-legged guardian perched atop a cluster of pale eggs—Amazochroma, a harvestman spider, diligently guarding its brood. He snapped a photo and uploaded it to iNaturalist. Half a world away, that single observation helped scientists reconstruct, for the first time, the evolutionary journey of parental care in one of arachnids’ most diverse lineages.
Parental care is rare in the animal kingdom, especially when males take the lead. But in harvestmen—often mistaken for spiders—paternal guarding has evolved independently more than half of all known times across arthropods, despite the group making up just 0.6% of arthropod diversity. Now, thanks to a fusion of decades of fieldwork and a surge of citizen science data, researchers led by Glauco Machado at the University of São Paulo have mapped how maternal and paternal care emerged, vanished, and reappeared across 6,900 species in the superfamily Gonyleptoidea. Their findings, published in the Zoological Journal of the Linnean Society, reveal a complex evolutionary story shaped by survival, sex, and surprising reversals.
Before this study, scientific literature had documented parental guarding in just 80 harvestmen species over nearly 90 years. Machado’s team added 125 new records in weeks—62 of them pulled from iNaturalist in just two days. One photo at a time, amateur naturalists had captured fleeting moments of devotion: Deltilagus males cradling egg masses, Quindina parents standing watch over nests. These observations allowed the team to trace how maternal care evolved only from species with no care at all—mirroring patterns in insects—while paternal care arose either from no care or, remarkably, from maternal care. When males took over from females, the researchers suggest, it may not have been about survival alone, but about sex: a phenomenon called "enhanced fecundity," where females prefer males already caring for eggs, giving those males greater reproductive success.
The implications stretch beyond spiders. iNaturalist has become a force multiplier for global science, especially for researchers in the Global South who face barriers to museum collections and costly field expeditions. "It’s a tremendous source of information that can improve the velocity with which we accumulate biological information," Machado said. "I would never be able to do this by visiting museums around the world. It would be very expensive, very time consuming, but here we conducted the search in only one week."
Still, citizen science doesn’t replace expertise. Taxonomists were essential to verify species identities, determine the sex of caregivers, and distinguish true parental care from similar behaviors like mate guarding. As Machado puts it: we can’t protect what we can’t name. And names come from taxonomists. With biodiversity vanishing faster than we can catalog it, the partnership between public curiosity and scientific rigor has never been more vital. In the quiet vigil of a harvestman father guarding eggs, we see not just devotion—but the future of discovery.