First of all a happy Easter to you 🙂
This sunday, the spotlight is on the harvestman (Opiliones). Biological speaking, not an actual spider in the sense that it doesn’t belong to the same order as the true spiders (Araneae). But, since the harvestman belongs to the same class (Arachnida) as the other spiders and people often make the mistake of thinking that it is a true spider, I will include it in this series.
So what are the differences? The biggest difference is that in spiders, there is a clear distinction between the cephalothorax and the abdomen. Harvestmen also have these parts, but they look fused together like a big oval shape. Harvestmen have only two eyes, whereas spiders have eight eyes (some species have a different amount of eyes). Spiders produce silk or are venomous unlike the harvestmen. Harvestmen can however eat solid chunks of food. Spiders use venom to liquefy their prey and then proceed to suck the nutrients out of the body.
Interestingly, harvestmen can lose a leg on purpose (a phenomenon called autotomy) to distract predators. In some species, the legs keep twitching for a good amount of time after they were detached from the body. I have sometimes seen harvestmen with as little as 3 legs! Another distraction method is vibration of the body (which poses a real challenge when trying to photograph them) and secretion of foul-smelling chemicals. Harvestmen also secrete adhesive solutions, to trap prey, glue eggs and for adding camouflaging dirt to their bodies and eggs.
The Latin name Opiliones means “sheep-masters” after the (now abandoned) use of stilts by European shepherds. If a harvestman stands up straight on its long legs, it resembles these stilt-using shepherds. The name “harvestman” is derived from the period they are most often seen: harvest season.
Opiliones are a neglected group in biological research, so not much else is known about this group. Fortunately, in recent years, biologists have started to pay more attention to these creatures, so let’s hope that this continues!