by Shannon Farley

They might look like spiders with their eight very long legs, but they are completely different animals.

Harvestmen – often called daddy longlegs – are interesting arachnids that belong to the taxonomic order Opiliones, while spiders belong to the order Araneae. They are relatives of spiders, scorpions, and ticks, which are also arachnids. But while harvestmen are very similar to spiders in body shape, they are easy to tell apart once you know what to look for.

How to tell the difference between a spider and a harvestman? Spiders’ bodies are divided into two distinct parts by a “waist”, whereas the body of a harvestman is fused in a pill shape or like a ball with many legs. Most spiders have eight eyes (although they may have two or six) while harvestmen have only two eyes. Another difference is that harvestmen do not produce silk to make webs, and they do not have venom glands to hunt their prey. This means that harvestmen, or daddy longlegs, are harmless to humans.

The Opiliones are painted as part of the study to give them individuals ID – a technique used by Andrés and Rosa, those are not their natural colors.  Also, the paint doesn’t interfere with their behavior.
Photo Rosannette Quesada

There are more than 6,650 species of harvestmen across the planet, and new species are still being discovered. Fossil records show they’ve been around for a long time. In Costa Rica, there are many kinds of harvestmen living in tropical forests.

Recently, two different scientific research papers have been published on harvestmen found at Veragua Rainforest. Costa Rican ecologists Rosannette Quesada-Hidalgo, Ph.D. and Andres Rojas each conducted studies on the species of mud-nest harvestmen at the Veragua Rainforest, working at the Biological Station operated by The Foundation for Rainforest Research (the Veragua Foundation).

Rojas, who is a former biologist and guide at the Veragua Rainforest, holds a master’s degree in ecology and is working on his Ph.D. in Ecology at the Institute of Bioscience at the University of São Paulo in Brazil. Quesada-Hidalgo received her Ph.D. in Behavioral Ecology from the Institute of Bioscience at the University of São Paulo and is currently a volunteer at the Smithsonian Tropical Research Institute in Panama.

Both scientists say that although harvestmen are very diverse and abundant in the tropics, there is little known about them. This could be because the animals are mostly nocturnal and live in forests and because the field of Arachnology is only just beginning in Central America. In the U.S., on the other hand, most people are familiar with harvestmen, or daddy longlegs, because they are found in backyards, barns, gardens, etc. 

Photo Andrés Rojas

The scientists chose Veragua for their research due to the unique characteristics of the forest. “Veragua is a well-protected primary forest with big trees that naturally fall and create the perfect habitat for the mud-nest harvestmen. Because of its location in the Caribbean, and the humid and rainy climate, this forest is also the habitat for many other species of Opiliones that also caught my attention during my research,” said Quesada-Hidalgo.

“Veragua has a research station with the perfect infrastructure that allowed me to venture into the forest at night and come back to stay in a safe place, with all the facilities for researchers such as a restaurant and laboratories,” she added. Photo Julián Solano

It was the particular behavior of male mud-nest harvestmen that caught the researchers’ attention. “The nest construction behavior and exclusive paternal care of this species are very rare and interesting,” said Rojas.

In the species of mud-nest harvestmen found in the Caribbean region of Costa Rica, males build a nest of mud and organic matter on rotten tree trunks or branches of trees near the ground. The nest consists of a circle-shaped floor, approximately 4 cm in diameter, surrounded by a circular wall of approximately 1 cm in height. The males remain inside their nest for several months, where they receive visits from different females who live in the area. Some females copulate with the male and place their eggs on the nest floor and then leave. The males then efficiently take care of the eggs on their own until they are born, and there are even males willing to adopt nests. One of the studies found that the foster males were just as efficient as the original nest-owner males in caring for the eggs. This behavior prompted Quesada-Hidalgo to name her study “The Good Fathers.”A male of the harvestman Quindina limbata inside his arena-like mud nest on a fallen log in Costa Rica. The nest consists of a circle-shaped floor, approximately 4 cm in diameter, surrounded by a circular wall of approximately 1 cm in height. The males build their nests and remain inside them for several months, where they receive visits from different females who live in the area.
Photo Diego Solano

She has been so captivated by harvestmen (Opiliones) that she launched the Opilio Tracker project on social media to increase the general public’s knowledge about the animals.

“They are harmless and elegant creatures and we can learn a lot from their behaviors. I think Opiliones can be a tool to teach people not to be afraid of arachnids or bugs in general,” said Quesada-Hidalgo. “It’s natural that we are afraid of things we don’t know. So, many people are afraid of insects or arachnids. But if we can teach people, for example, that Opiliones are harmless because they have no venom and there is no reason to kill them, we probably won’t smash them the next time; and the same can happen with spiders or any other creature.”