Harvestman

This morning was pretty chilly and not much was out in the way of tiny invertebrates. I was trying to get a better angle on a small spider who was hiding in a curled leaf, and as I stood up to move to the other side, I saw an absolutely gigantic opilionid, a harvestman, sunning itself on the leafy bush next to me. A much better opportunity. I ended up finding about a half dozen harvestmen in and around the bush, and a few one the surrounding trees as well.

They look like spiders — they are fellow arachnids — but there are a few important differences. For one, they don’t spin webs (they lack the organs to) and have no venom at all. They mostly prey on soft-bodied animals like aphids, and actually have some value in agriculture as a species that contributes to keeping down pest levels. They’ll also scavenge and cannibalize.

You can tell a opilionid from a spider quickly by two obvious clues. First, opilionids have two eyes mounted on a tubercule along the midline of the body, instead of the eight eyes spread along the front of a spider’s body. Spiders and harvestmen both have a body composed of two main segments, a cephalothorax (the front head-torso region) and an abdomen, but while spiders have a narrow pinching waist that clearly marks where one ends and one begins. The two sections are much harder to determine in opilionids.

I’m pretty certain that the species I photographed is Phalangium opilio, and the bolder markings along the abdomen seem to imply that I found females. I am open to correction on both of these points.