Harvestman, Daddy Longlegs, Shepherd Spider, Grandfather Greybeard: all colloquial names for members of the Opiliones order. Yes, they have eight legs, but they’re not actually spiders. In fact, according to Chris Buddle, professor of arthropod ecology at McGill University in Montreal, Canada,
“Comparing a spider to a harvestmen is like comparing a blue whale to a chimpanzee.”
But how do you tell the difference between a harvestman and a spider? Well, harvestmen don’t have a waist or separate abdomen. Cellar spiders are often mistaken for harvestmen because of their long spindly legs, but they have a definite waist and also make silk. And don’t get confused about Daddy Longlegs either. Chris was surprised to learn that in the UK what we call the Daddy Longlegs is actually a crane fly.
If you want to know more about these unfamiliar creatures, you can buy the book by Ricardo Pinto-da-Rocha, Glauco Machado and Gonzalo Giribet called Harvestmen: The Biology of Opiliones.
This will set you back about £100, though, so you’d have to be pretty interested to shell out that kind of money.
Chris Buddle bought the book. He has studied other eight-legged creatures, such as pseudoscorpions and wolf spiders, but he didn’t know very much about harvestmen at all. Having paid out all that money, he then wanted to make sure he read the book, so he started the Twitter hashtag #OpilionesProject, with the authors’ permission. As he told me when I contacted him at his office,
“I didn’t care if other people were interested. I did it, initially, for entirely self-serving reasons. The motivation was to give me time and motivation to read the book and get used to Twitter.”
His first tweet was on April 3rd 2012 and it took him until February 26th 2013 to finish the book. They are not the typical “charismatic” animal that so captivates public imagination, so he was surprised, but delighted, to find a pretty passionate bunch of people who were interested in the details and beauty of these understudied creatures.
So, what did we learn about Opiliones? They don’t make silk, they’re not venomous and some of them glow under UV light like scorpions do. Unlike all other arachnids, the males “present intromittent genitalia derived from the male reproductive tract” i.e. they have penises. They aren’t hunters like spiders, for the most part, but tend to scavenge. From time to time they form aggregations, where they group together for several weeks, or even months. The largest aggregation on record was 70,000 individuals! Nobody knows quite why they do this, though defence against predators and regulating body temperature have been suggested.
And there are lots of other things we don’t know about them. I asked Chris what the most important areas of research are. He said we still don’t know the fundamental life history of an individual, understanding of their physiology and development needs work, and it would be good to get some studies of their diversity. This is all pretty basic stuff, why don’t we know this? Chris has an idea:
“There are some really serious phobias out there. I’m very aware of that. Phobias prevent study of arachnids.”
Not for everyone, though. In fact, Chris got a lot of queries for tips on how to capture and keep harvestmen by interested amateurs, so we may get results from some citizen science. Meanwhile the main aggregation of opilionologists seems to be in Brazil, so expect more stories about Brazilian arachnids.
Though the Opiliones Project is over, Chris has compiled the tweets into a pdf that you can download from his blog, Arthropod Ecology. But he did admit to having glossed over those chapters that didn’t translate into 140 characters, like taxonomy and physiology, so if you’re interested in swelling the ranks of scientists studying the Opiliones order, you better buy the book for yourself.