The availability of photos and records of the natural world has increased thanks to the rise of citizen science apps such as ebird, ebutterfly and iNaturalist. Researchers at the Smithsonian Tropical Research Institute (STRI), Universidade de São Paulo (USP) and other institutions, saw an opportunity to combine these citizens' pictures with observations made by scientists, to understand the evolution of a very particular behavior: harvestmen taking care of their eggs. Scientists gathered this information in a recent publication in the journal Zoological Journal of the Linnean Society.
Harvestmen, popularly known as daddy long legs, are harmless arachnids that look like spiders but are not considered spiders, as they don't produce silk or have any venom. They belong to an arachnid group called Opiliones. In many species of the superfamily Gonyleptoidea, which is the group containing the most documented cases of care in harvestman and the focus of this study, either the male or the female cares for clutches of eggs (and very rarely of the young). The care performed by males is an uncommon behavior among animals and of especial interest for biologists. In many other species within this group, the eggs are laid individually by females in hidden places in the forest, such as under logs and inside natural crevices. These species lack the care provided by their parents, a behavior called parental care. In many species the presence or absence of care, or if the individual that cares is the male or the female, is unknown to scientists.
By reviewing 24,000 photos shared on the citizen science platform iNaturalist, scientists recorded the presence or absence of parental care in 53 species. Together with new field and laboratory observations from 19 researchers across five Latin American countries, information on the care for 85 species was discovered, data that was previously unknown to science!
"This study shows how photographing wildlife can produce a major scientific advance. By combining iNaturalist images with scientific observations, we more than doubled the number of harvestman species with data on parental care," said professor at the Instituto de Biociências of Universidade de São Paulo (IB-USP) in Brazil and lead author of the study, Glauco Machado.
The information helped create a family tree of the evolution of care in the group Gonyleptoidea, which is especially diverse in the Neotropics. Scientists discovered that maternal care evolved only from ancestors that lacked parental care. Paternal care, however, followed two evolutionary paths: it evolved either directly from species without parental care or from species with maternal care.
"The paper brings together two themes with broad appeal: the evolution of parenthood and the power of citizen science. It also shows that the same approach (the use of photos from iNaturalist) can be used to study many other animals and behaviors, far beyond harvestmen," explained Machado.
Many of the citizens who uploaded these photos probably didn't know they were documenting something new to science, a sign that curiosity can lead to remarkable discoveries.
"People can contribute simply by observing nature, taking good photographs from several angles, and uploading them to platforms such as iNaturalist. A photograph that seems ordinary may document a behavior unknown to science and help researchers answer much larger evolutionary questions", added Machado.
Reference: Machado, G., Buzatto, B. A., Caetano, D. S., Flores, E., García-Hernández, S., Grob, O., ... & Villarreal, O. 2026. One small step for citizens, one giant leap for science: iNaturalist records boost our understanding of the evolution of parental care in a clade of arachnids. Zoological Journal of the Linnean Society, 207(2), zlag061.
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