Our first independent project: Opiliones

At La Selva, we were to complete our first independent project.  Little did I know how difficult it would be to simply come up with an idea for a successful project.  However, my group of four finally decided to do our research project on Opiliones.

Opiliones, also called harvestmen, or daddy long legs, are known for their small bodies and their eight long, thin legs.  Of the eight legs, six are locomotor legs, while the other two longer legs are considered sensory legs.  Opiliones are NOT spiders, but rather arachnids.  There are a few major ideas that propelled our research project.  The first is that different species in general use a variety of different tactics to avoid predation.  Opiliones follow suit, as they also use a variety of anti-predator methods for survival.  One line of defense is autotomy, or voluntarily self-amputating a leg, when trying to escape from a predator.  Many Opiliones may be missing one or more locomotor legs, sensory legs, or both.  Other methods include, but are not limited to, the act of bobbing their bodies up and down to confuse predators.  Bobbing up and down rapidly makes it harder for the predator to identify and pinpoint an attack on an individual.  Another defensive mechanism is the act of fleeing or running away to try to escape from a predator.  Lastly, and most importantly for our research project, Opiliones tend to live in groups for protection.   By living in groups, each individual lessens its chance of being preyed upon, or “diluting” its chances of being eaten, known as the dilution effect.  So the main question driving our research project was does group size, configuration (are they spread 0 - 5 cm apart, are they clustered, or are they stacked on top of each other), and/or number of legs (all 8 legs, missing locomotor, or missing sensory legs) on an individual receiving a stimulus effect the defense mechanisms of aggregated harvestmen?

After four days in the field searching for groups of harvestmen, we found and tested 119 groups whose membership ranged from 3 to 165 individuals.  Our tests consisted of prodding an individual possessing either 8 legs, missing locomotor legs, or missing sensory legs.  The individual Opiliones tested were located on the edge of the group and prodded with a pencil once every 30 minutes (3 trials per group).  We observed the groups reactions, and noted if they ran, bobbed, ran then bobbed, or didn't respond at all.

Finally, after collecting all of our data, we analyzed everything we gathered from the field.  We found aggregations of Opiliones do not respond differently to disturbed individuals if they are missing a locomotion/sensory leg, or not missing any legs.  Our results also concluded that clustered and spread aggregations showed significantly different responses to stimulus, and that reactions will vary significantly in relation to group size and group density.

We learned a lot about Opiliones when doing our research project, but we also learned to work as a team.  We had a large amount of work, but everyone worked together.  Some of the work was tedious and sometimes physically draining, however, being able to see the results made everything worthwhile. 

Jordan General

Duke University