Why Thousands of Daddy Longlegs Form Huge Clusters

Some people cannot cope with a single daddy longlegs in their bedroom—or even worse, in a tent—but can you imagine coming across thousands of them grouped together?  In this extraordinary YouTube clip, you can see so many of them in a cluster that their legs look a bit like a furry animal or some creepy hair. To form these clusters, the individuals in the middle grip the side of the wall with their mouths, while additional layers attach themselves to the cluster using their legs. Take a look at the clip for yourself and then read on to discover what these creatures are doing.

What Exactly Are Daddy Longlegs?

Daddy longlegs are also called harvestmen and are classed as arachnids because they lack antennae (which would make them an insect). They belong to the Opilione order. Harvestmen have a small body with a tough cuticle and tubular, jointed legs which can be 20 times longer than their body! Thanks to these extraordinary legs, they can move fast, keeping off the ground, and clambering around vegetation.

Their body is not divided into two segments (as in spiders), and they cannot spin silk. While they are mostly nocturnal, you will see some out during the day. The rest of the time, they are hiding in leaf litter, under ivy, or among grass stems. They are also often spotted inside cool, damp buildings and in outdoor toilets, where they are not always welcome! There are over 6,000 species, and they are found in most parts of the world. Harvestmen eat a wide range of food, including dead slugs, bird droppings, and small invertebrates.

When and Where Do They Cluster?

Harvestmen clusters are most common in cooler weather, as they huddle together to conserve warmth and moisture. There are several clips online of clusters on the sides of buildings and on walls, particularly under overhangs, around crevices, under picnic tables, and under bridges. Several species can also be found clustered in dark, moist areas at the entrance to caves.

There are several theories to explain this behavior. One suggests that, because they prefer moist environments and are prone to drying out, clustering together helps them maintain optimal humidity. Another theory is that clustering provides defense. Since they are not venomous and cannot spin silk, gathering in large numbers may help deter predators. The movement of their legs can resemble a larger animal, which may scare off potential threats. Additionally, daddy longlegs can release a foul-smelling secretion, and when many individuals do this simultaneously, it is more effective. Clusters can sometimes contain hundreds or even thousands of individuals, though exact numbers for the largest gatherings are not well-documented in scientific literature.