Research Reveals Evolution of Parental Care in Harvestmen

Research led by the University of São Paulo and published in the Zoological Journal of the Linnean Society used iNaturalist data to more than double the documented cases of parental guarding in harvestmen. The study found that paternal care often evolves from maternal care, a process likely driven by sexual selection and “enhanced fecundity.”

How did citizen science double the known data on harvestmen?

Between 1936 and 2025, scientific literature recorded parental guarding behavior in 80 species of harvestmen. Glauco Machado and his international team used the iNaturalist database to find 62 additional records in just two days. This surge in data allowed researchers to reconstruct the evolution of maternal and paternal care in the superfamily Gonyleptoidea for the first time.

Machado noted that the velocity of data accumulation through citizen science far exceeds traditional museum visits or fieldwork. The accessibility of georeferenced observations removes the high costs and time constraints typically associated with large-scale biological research.

Why is paternal care in harvestmen an evolutionary anomaly?

The study reveals a distinct split in how parental care evolves. According to the researchers, maternal care only evolved from a state of no care, mirroring patterns seen in insects. Paternal care, however, evolved from either no care or from existing maternal care.

When paternal care emerges from maternal care, Machado theorizes it is a result of sexual selection. This “enhanced fecundity” hypothesis suggests that females prefer males who demonstrate caring behavior toward eggs, making the trait an evolutionary advantage for the males.

This pattern suggests that different selection pressures drive the evolution of fathers versus mothers in the arachnid world. For more on how evolutionary traits shift, see our guide on adaptive biological behaviors.

What role do taxonomists play in the age of crowdsourced data?

While platforms like iNaturalist can amass data quickly, the study emphasizes that human expertise remains irreplaceable. Machado argues that taxonomists are essential to correctly identify species and distinguish between the sex of the caregiving individuals.

Without this expertise, researchers cannot differentiate between actual parental care and “mate guarding,” a superficially similar behavior. Machado stated that taxonomists’ roles are more important than ever because a species cannot be preserved if it doesn’t have a formal name.

How does iNaturalist change research for the Global South?

Traditional biological research often requires expensive travel to global museums or funding for extensive fieldwork. By utilizing open-access databases, scientists in the Global South can conduct large-scale research without these financial barriers.

The University of São Paulo team demonstrated that a week of digital searching could replace years of physical travel. This shift democratizes scientific discovery, allowing researchers to analyze global biodiversity trends from their own institutions.

However, the study acknowledges a persistent “sampling bias.” It’s easier for a citizen scientist to photograph and upload a harvestman guarding eggs than it is to record a species that provides no care. This means the data may overrepresent caregiving species.

Future Trends: The Integration of Crowdsourcing and Taxonomy

The success of the harvestmen study points toward a future where “hybrid research” becomes the standard. We can expect to see more studies combining decades of legacy literature with real-time data from platforms like iNaturalist to map rare behaviors in frogs, insects, and other arthropods.

As AI-assisted identification improves, the bottleneck will shift from data collection to data verification. The demand for professional taxonomists will likely evolve into a role of “data auditors” who validate the massive streams of information provided by millions of amateur naturalists.

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