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

Citizen science data from popular platform iNaturalist has helped uncover the evolution of parental guarding behaviour in harvestmen, 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 have 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 has found that parental guarding behaviour has evolved, disappeared, and then re-emerged several times throughout the evolutionary history of harvestmen. By mapping this behaviour, 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 theorised that when paternal care evolved from maternal care, it is likely evidence of a sexually selected behaviour; a hypothesis known as ‘enhanced fecundity’.  

With over 6900 species currently recognised, harvestmen represent one of the most diverse orders of arachnids in the world. Despite accounting for only 0.6% of arthropod diversity, they represent over 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.  

Lead author Glauco Machado explained: “It’s very rare in nature, paternal care, and this behaviour evolved many times independently. So, by looking at harvestmen we can explore questions related to the factors that led to the evolution of this behaviour. In many species where males care for the offspring alone, the caring activity is a sexually selected behaviour, 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 their ‘Big Garden Bird Watch’, 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 utilising citizen science in bird research, Machado and his team made use of global citizen science database iNaturalist, where users can upload georeferenced observations of organisms found across the world, to expand their dataset. The rate of data collection from iNaturalist has proven to be much faster than traditional scientific work. Between 1936-2025, scientific literature documented parental guarding behaviour in 80 species of harvestmen; this study more than doubled this 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 datasets. 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.” 

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 emphasises that taxonomic expertise is still necessary to correctly identify the species and recognize the sex of the caregiving individuals.  and distinguish between superficially similar behaviours 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/absence of care. Given more than half of records in this study were new, Machado hopes that scientists continue to explore the use of citizen science platforms in 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.”