Devoted dads and citizen science: The evolution of parental care in harvestmen spiders is uncovered

Citizen science data from the popular platform iNaturalist has helped uncover the evolution of parental guarding behavior in harvestmen spiders, as shown in research published in the Zoological Journal of the Linnean Society.

Combining nearly three decades of fieldwork with data from iNaturalist, an international team of researchers led by a scientist from the University of São Paulo has more than doubled the number of documented cases of parental care in harvestmen. As a result, the evolution of maternal and paternal care in the superfamily Gonyleptoidea was reconstructed for the first time.

The study found that parental guarding behavior has evolved, disappeared and then reemerged several times throughout the evolutionary history of harvestmen. By mapping this behavior, researchers found that maternal care evolved only from no care, a pattern also seen in insects. However, paternal care was shown to evolve from either no care or from maternal care, suggesting different selection pressures were at play. The researchers theorized that when paternal care evolved from maternal care, it was likely evidence of a sexually selected behavior, a hypothesis known as “enhanced fecundity.”

With more than 6,900 species currently recognized, harvestmen represent one of the most diverse orders of arachnids in the world. Despite accounting for only 0.6% of arthropod diversity, they represent more than half of the independent origins of paternal care, a rare trait in the animal kingdom. This offers a unique opportunity to study the evolutionary development of parental care on a broader scale.

Why harvestmen are unusual

Lead author Glauco Machado explained, “It’s very rare in nature, paternal care, and this behavior evolved many times independently. So, by looking at harvestmen, we can explore questions related to the factors that led to the evolution of this behavior. In many species where males care for the offspring alone, the caring activity is a sexually selected behavior, which means that females prefer males that are caring for the eggs.”

Citizen science allows anyone to lend their time and curiosity to projects around the world, without the need for specialist knowledge. From recording garden bird populations for the RSPB as part of its “Big Garden Bird Watch,” to rediscovering a lost species of grasshopper in Australia and even uncovering an ancient writing system in cave art, citizen science data has proven to be an expanding resource in modern research.

Inspired by a talk on utilizing citizen science in bird research, Machado and his team made use of the global citizen science database iNaturalist, where users can upload georeferenced observations of organisms found across the world, to expand their data set.

The rate of data collection from iNaturalist has proven to be much faster than traditional scientific work. Between 1936 and 2025, scientific literature documented parental guarding behavior in 80 species of harvestmen; this study more than doubled that number, with 62 records coming from iNaturalist alone. Machado and his team were able to do this in only two days.

The significance of iNaturalist reaches far beyond expanding data sets. Machado stresses that its true value lies in the accessibility of this resource to scientists worldwide. “It’s a tremendous source of information that can improve the velocity with which we accumulate biological information. 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.”

Citizen science speeds discovery

By removing access costs and the need for timely and expensive fieldwork, citizen science platforms are transforming traditional research and opening opportunities for large-scale research by scientists in the Global South.

The study also highlights the importance of taxonomists in modern research. While citizen science platforms can amass huge amounts of data very quickly, Machado emphasizes that taxonomic expertise is still necessary to correctly identify the species, recognize the sex of the caregiving individuals, and distinguish between superficially similar behaviors such as parental care vs. mate guarding.

“I think taxonomists’ role in modern science is more important than ever. We cannot preserve a species that doesn’t have a name. And names are provided by taxonomists. So, it’s very important.”

Though a remarkable breakthrough, the study doesn’t come without its limitations. Sampling bias remains a challenge in parental care studies, for the simple fact that it’s easier to record instances of parental care than of no care. Yet the authors argue that studies such as this one are filling major gaps in our knowledge regarding the presence or absence of care.

Given that more than half of the records in this study were new, Machado hopes that scientists continue to explore the use of citizen science platforms in the future. “I think it’s a very broad contribution for people that are working with insects, frogs, and all kinds of groups, animal groups, in which we have both maternal care and paternal care.”

Who’s behind this story?

Gaby Clark

MA in English, copy editor since 2021 with experience in higher education and health content. Dedicated to trustworthy science news.

Full profile →

Robert Egan

Bachelor’s in mathematical biology, Master’s in creative writing. Well-traveled with unique perspectives on science and language.

Full profile →