Arachnaphobe studies daddy long legs, survives

Opiliones are not spiders. That was the logic my group members used when they were trying to convince me to conduct our independent project on a specific type of daddy long legs. I’m not a fan of spiders. I understand that they are an important facet of many ecosystems (including those found in La Selva), but something about them makes my skin crawl. And while it is true that these arachnids aren’t spiders (which belong to another order entirely), I wasn’t especially enthusiastic about the choice of study organism. In fact, I dragged my feet during every step of the planning process, debated leaving the group, and complained more than I would like to admit. Despite my initial reluctance, I ended up enjoying the data collection process immensely, which is at least partly (if not mostly) due to the fact that it gave me a legitimate excuse to poke living organisms with a stick.

We chose to study opiliones because they exhibit two interesting defense strategies: autotomy and aggregation. Autotomy is the ability to voluntarily drop limbs in the face of predation (for example: some lizards can drop their tails). Aggregation is the tendency for members of a species to gather together into large groups. Aggregations of opiliones will all vibrate simultaneously in the face of perceived danger, which is meant to confuse and intimidate predators (it’s definitely a striking visual when you see it). Since opiliones commonly lose legs from autotomy, we wanted to see whether the number of legs on a predated individual affects the response of the group (whether they disperse, vibrate, or do nothing). We thought that opiliones that were missing legs might be more likely to react to stimulated predation (being poked with a stick) and inform the group, since they were not as naïve to the costs of predation. We wandered around La Selva poking aggregations of opiliones and recording the groups’ responses. After sampling 119 groups which ranged in size from 3 to 165 individuals (2,454 opiliones total!), we found that groups did not respond differently based on the number of legs of the individual poked. We did find that larger groups were more likely to vibrate while smaller groups were more likely to disperse, which makes sense given that group vibration is more intimidating if the group is large.

I really enjoyed the opportunity to design and execute an independent research project, and I learned a lot about fieldwork in the process. I’m grateful to my group for encouraging me to stick with the project when I initially wasn’t interested; I found that while I still don’t like spiders, I don’t mind opiliones because after all, they’re not spiders.

Rose Hinson

Duke University