Citizen scientists have been helping researchers understand how parental care evolved in harvestmen, a group of spider-like arachnids, by contributing observations through the popular nature platform iNaturalist. The survey results are Zoological journal of the Linnean Societyreveals that parental defensive behavior has appeared, disappeared, and evolved again many times over the evolutionary history of the group.
By combining nearly 30 years of field research and observations submitted to iNaturalist, an international team led by scientists from the University of São Paulo has more than doubled the number of documented cases of parental care in harvesters. The expanded dataset also allowed researchers to reconstruct for the first time how both maternal and paternal care evolved within the superfamily Gonileptoii.
Citizen science reveals the evolution of parental care
The analysis revealed that parental defensive behavior does not follow a simple evolutionary path. Instead, it repeatedly appeared, was lost in some lineages, and later reappeared.
The researchers found that maternal care evolved only from species that do not exhibit parental care, consistent with a pattern previously observed in insects. However, paternal caregiving followed two different evolutionary routes. The disease either arose directly from species without parental care, or from species where the female was already guarding her eggs. This suggests that different evolutionary pressures have shaped the development of maternal and paternal care.
The researchers propose that when paternal care evolved from maternal care, it likely reflected a form of sexual selection known as “fertility enhancement,” in which females prefer males who have already taken care of their eggs.
Why Harvestmen are perfect for learning to be fathers
More than 6,900 species of harvesters have been identified, making them one of the most diverse groups of arachnids. Although they represent only about 0.6% of all arthropod diversity, they account for more than half of the known examples of uniquely evolved paternal care among arthropods, making them an exceptional group for studying the evolution of child rearing.
Lead author Glauco Machado explained:
“Paternal care is very rare in nature, and this behavior has evolved independently many times. Therefore, by observing harvesters, we can explore questions related to the factors that led to the evolution of this behavior. In many species where males care alone for their offspring, caregiving is a sexually selected behavior, meaning females prefer males who care for eggs.”
iNaturalist has dramatically expanded its dataset
Citizen science projects allow people without professional scientific training to contribute valuable observations. Around the world, volunteers have helped monitor bird populations, rediscover lost species, and even discover ancient writing systems through cave paintings. Their contributions are an increasingly important source of scientific data.
Machado’s team turned to the global iNaturalist platform after hearing a presentation on using citizen science in bird research. This website allows users to upload georeferenced observations of plants and animals from almost anywhere in the world.
The results demonstrated how citizen science can quickly accelerate research. Scientific studies published from 1936 to 2025 have recorded parental vigilance behavior in only 80 harvester species. Using iNaturalist, the researchers more than doubled that total, including 62 new records provided by the platform alone. Machado said the iNaturalist search itself took only two days.
Citizen science accelerates research around the world
According to Machado, iNaturalist’s biggest strength is not just the number of observations it includes, but the ability to access those records by scientists everywhere.
“This is a tremendous resource that can increase the rate at which biological information accumulates. You could never do this by visiting museums around the world. It’s very expensive and time-consuming, but here we did the search in just one week.”
By eliminating many of the costs associated with museum visits and extensive fieldwork, citizen science platforms are making large-scale biological research more accessible, especially for scientists working in the Global South.
Taxonomists remain essential
Despite the growing value of citizen science, the researchers stress that professional taxonomists remain essential. Correctly identifying the species, determining whether the caregiver is male or female, and distinguishing between true parental care and similar behaviors such as mate guarding all require specialized expertise.
Machado emphasized the continued importance of taxonomy.
“I think the role of the taxonomist in modern science is more important than ever. You can’t save a species without a name, and the name is provided by the taxonomist. So it’s very important.”
Research limitations and future research
The researchers acknowledge that the study has limitations. One of the biggest challenges is sampling bias. This is because animals that actively guard their eggs are much easier to notice and photograph than species that do not provide parental care.
Still, the authors argue that studies like this can help fill a major gap in understanding which species provide parental care and which do not. With more than half of the records analyzed being newly documented, Machado believes citizen science will continue to play an increasingly important role in studying parental behavior across different animal groups.
“I think this is a very broad contribution for people who work with insects and frogs and all kinds of groups and animal groups that are doing both maternal and paternal care.”
