Essays from Friedrich

Harvestmen

            Many of you have no doubt found it somewhat disconcerting to walk into the restrooms at Friedrich in late summer or early fall and see large, bouncing masses in the corners near the doorways.  This phenomenon is not unique to Friedrich, of course—nearly any outbuilding in the southern U. S. is likely to have clusters of harvestmen (aka daddy longlegs) at this time of year.  The dark corners of restrooms seem to be particularly attractive to these fascinating creatures, probably because these are areas with cooler temperatures and higher humidity.  But while these animals are commonly encountered, surprisingly little is known about their behavior, and much of the information that we pass on to one another about them falls into the realm of myth or urban legend.

            While the common name “daddy longlegs” is most frequently used when describing this group of animals, it is problematic for two reasons.  First, there are three species of this group that can be commonly encountered around San Antonio, but only one of these species has long legs.  The species that you usually see when entering the restrooms at Friedrich is Leiobunum townsendi.  It is rather famous for the dense clusters that it forms, sometimes consisting of thousands of individuals.  (By contrast, most related species form aggregations of only 20–30 individuals.)  Another of its distinguishing characteristics is the alternating light and dark bands of the legs.  You might occasionally spot one of the two short-legged species if you look closely at the walls, especially near the concrete floors,  This particular species tends to have a body that is noticeably orange in color, but its most obvious characteristic is that its legs are much shorter relative to the length of the body than in L. townsendi.  While I have not conclusively identified this species, it is likely a member of genus Eumesosoma or Vonones.  A third species, Dalquestia formosa, also has short legs but is not likely to be encountered around the restrooms.  This is a strikingly beautiful species that has a cobalt-blue or indigo base color with contrasting bright orange and white patches.  This species is much less numerous than the other two and tends to be found most commonly under rocks or logs.  As you can see from the descriptions of these three species, the term “longlegs” is justified for only one of them.  (The use of “daddy” or “granddaddy” is somewhat of a mystery!)

            A second reason that “daddy longlegs” should be avoided is that this one common name is often applied to two other groups of organisms.  In some parts of the world, insects that we usually refer to as mayflies are known as daddy longlegs.  Closer to home, there is a genus of spiders,Pholcus, that has very long legs relative to body length, so naturally they too are referred to as daddy longlegs.  For these reasons, I prefer the less problematic term “harvestman”.  This description apparently comes from the observation that the long-legged species begin to form their aggregations around harvest time in various parts of the world.

            You may have noticed in the preceding paragraph that I referred to spiders in a way that suggested that harvestmen are not spiders.  This is in fact the case—harvestmen are arachnids, but are not spiders.  Class Arachnida consists of nearly a dozen orders of organisms.  For example, ticks and mites are in order Acari, scorpions in Scorpiones, spiders in Araneae, harvestmen in Opiliones, and camel spiders, which have been made famous by the Internet, in Solpugidae.  Of the arachnids, the only ones to make silk are spiders; therefore, in part because harvestmen do not have this ability, they are placed in a separate order.

Click for larger image Photo by Cary Guffey©

A second characteristic that separates harvestmen from spiders is the lack of venom and fangs in the former.  You may have heard that harvestmen are deadly poisonous, but their fangs are too small to penetrate our skin.  This is strictly a myth as harvestmen have no fangs, but instead have tiny, crawfish-like pincers (see micrograph).  They also lack venom, probably because they have no way of administering it to potential predators or prey.  They do have a noxious secretion that oozes from two pores on their back and is used to deter would-be predators, but this apparently has few or no toxic effects.             Not only are harvestmen not dangerous to us, they are beneficial scavengers and they engage in a variety of fascinating behaviors (such as bouncing when predators are near, intertwining their prehensile legs in aggregations, and males fighting over mating sites).  So the next time that you walk by a writhing mass of them, rather than simply muttering “ Oooh!” and scurrying past, take a moment to notice the markings on their bodies and how they use their long legs.  And if you really want to feel like a naturalist, inspect the walls for other interesting species such as short-legged harvestmen and spiders that you can use for comparison.

Cary Guffey Ph.D., July 2004

Dr. Guffey is a member of the Board for the Friends of Friedrich Wilderness Park. He is a faculty member of the Biology Department of Our Lady of the Lake University and has conducted and published research on Harvestmen.