This species appears to be well camouflaged in its natural habitat – high elevation tropical wet forest with an abundance of mosses and ferns at Las Brisas Nature Reserve, Límon province, Costa Rica. Luckily I snapped some photos of this species before preserving a few individuals in ethanol to examine later in the lab because, unfortunately, the gorgeous color faded quickly! Upon closer inspection our research team discovered that the harvestman does not produce the green pigment, but rather, the pigment is produced by epizoic cyanobacteria that lives on the dorsal scute of the harvestman. This is an extraordinary example of the evolution of symbiosis. Although it is unclear whether this relationship is mutualistic (one would have to determine whether the cyanobacteria is actually benefiting), the green coloration does appear to provide camouflage for this harvestman within the very lush, green habitat in which it was observed.
During the arachnologist field trip to Toft Point in Wisconsin a couple weeks back, I was in the field collecting with opilionologist Jeff Shultz and arachnid photographer Joe Warfel. Jeff collected Caddo pepperella, a rare species of harvestman. Previously this species has only been collected in pitfall traps so this was the first time anyone has ever collected and photographed this species alive! I thank Jeff and Joe for giving me a chance to photograph the specimen.
Caddo pepperella is a tiny litter dwelling harvestman that very few people will ever observe out in the wild! The length of its body is less than ONE millimeter!!! And its legs are not much longer than a couple millimeters. But small as it is, relative to its body size, the eyes are huge!
Updated on 4/2/13 – species is Caddo pepperella, ID by J. Shultz.
The ubiquitous species of harvestman Phalangium opilio was named by Carl Linnaeus in 1758. P. opilio is now distributed all over North America, where it has been introduced from Europe (thankfully it is not a pest!). The species range has also apparently spread into parts of Asia and Africa. This species thrives in a number of different habitats, including natural habitats, such as forests, as well as anthropogenic habitats/structures, such as under bridges, in gardens or green spaces.
Males of P. opilio have large horns on their chelicerae (pointing outward, away from the anterior end). These structures are used as weapons in male-male contests which most often results in the loser fleeing and the winner having a chance to mate with a nearby female.
Below are a few more photos from a field trip to Toft Point, WI during the 2012 meeting of the American Arachnological Society at UWGB.
Notes on image below: The cheliceral horns are the long pointed cones sticking off of the first pair of appendages (the chelicerae). The chelicerae bend downward, each terminating in a movable, pincer-like claw that is not visible here. Note that the male pedipalps are very long, unarmed, and appear as if they are an additional pair of legs (here the pedipalps are more gold in color, while the legs are black). This male is also missing the second walking leg on the near side of the body.
Image below: Same male, dors0lateral view.
Image below: Female from a dorsal view. The pedipalps are shorter and are held close to the body partially covering the smaller chelicerae of the female.
Harvestmen: The Biology of Opiliones. 2007. R. Pinto-da-Rocha, G. Machado & G. Giribet (Eds.). Harvard University Press.
Willemart RH, Farine J-P, Peretti AV, Gnaspini P. 2006. Behavioral roles of the sexually dimorphic structures in the male harvestman, Phalangium opilio (Opiliones, Phalangiidae). Can. J. Zool. 84: 1763-1774.
At most academic meetings the arachnologists often get lumped into an entomology section. Or they might find themselves mixed in with general invertebrates. But not this time! Two weeks ago, in Green Bay, Wisconsin, more than 100 arachnologists from all over the world met for the annual meeting of the American Arachnological Society hosted by University of Wisconsin at Green Bay. The meeting took place over the course of four days and included all kinds of arachnid-based talks, posters, social events and an auction with all kinds of spider paraphernalia (books, t-shirts, toothbrushes, old photos, jewelry and more)! It was a great opportunity for many enthusiastic arachnologists to share their exciting research regarding the charming little animals that strike fear into the hearts of most people!
After the official meeting concluded there was a field trip to visit Toft Point State Natural Area, on a peninsula along the western shore of Lake Michigan. About 40 arachnologists jumped on a bus, headed up to Toft Point, and collected specimens in hopes of adding to the list of known arachnids from this site. Here are a few spider photos from the field trip.
Longlegs fact #4: Harvestmen have repugnatorial glands that produce compounds used in chemical defense.
These repugnatorial glands are also known as defensive glands, scent glands, stink glands or odoriferous glands. The repugnatorial glands are a major synapomorphic character of Opiliones. This means that the glands are a derived character, shared among all Opiliones (and their most recent common ancestor), but not among other arachnid groups (though other arachnids may have different chemical defense mechanisms). The glands produce chemical compounds that are meant to deter predators. The chemical compounds produced are very diverse but many are forms of quinones and phenols. The openings of the glands are on the body near the second pair of legs. The harvestmen usually release this secretion when threatened or disturbed.
The chemical compounds produced by some species can actually be detected by our own senses. When I collect harvestmen by hand I will sometimes smell them just out of curiosity (despite the crazy looks I get). The chemical compounds produced by some species are surprisingly potent! If I were a natural predator of harvestmen I would think twice about consuming them after getting a whiff of this. And no, I have not tried tasting them! Yet.
Although there will be many more interesting stories and facts that I will share about harvestmen in future posts, this post will conclude my series on the introduction to the biology of harvestmen.
Longlegs fact #3:
With more than 6,500 species, Opiliones represent the third largest order of Arachnida. The largest arachnid order is mites/ticks (order Acari) with more than 50,000 described species, followed by spiders (order Araneae) with more than 40,000 species. For a better frame of reference consider this: there are approximately 5,700 species of mammals in the world while there are more than 350,000 species of beetles in the world.
Almost every time I travel to a new place in Central America to collect harvestmen, new species are collected. So there’s plenty more work to be done in understanding and describing the diversity of this group.
Below are more photos of harvestmen from Costa Rica.
So we’ve already established in the previous post that daddy longlegs, also known as harvestmen, are NOT spiders. So let’s go ahead and tackle another big myth surrounding daddy longlegs.
Longlegs Fact #2: Daddy longlegs are NOT venomous.
Daddy longlegs have no venom glands or fangs despite that rumor you may have heard that “daddy longlegs are the most venomous spider in the world, but their fangs are too small to penetrate our skin”. Whereas spiders are fluid feeders (the venom has enzymes that digest the tissue first and then the spider sucks up the fluids), daddy longlegs are whole feeders (they tear apart their food with their chelicerae). The chelicerae of harvestmen are pincer-like with one stationary and one movable claw, however, they cannot bite and are in no way harmful. In contrast, the chelicerae of a spider are the pair of fangs which inject venom.
So where does this rumor come from? Well some people suggest that it has to do with the confusion of overlapping common names – which is one reason why scientists use Latin names and have many rules that they must follow when formally naming a species (for animals, these guidelines are established by the International Commission on Zoological Nomenclature).
In Ireland, for example, the common name “daddy longlegs” refers to crane flies. So it is obvious how common names may be a sources of confusion, but it doesn’t explain how we have managed to incorrectly label daddy longlegs as “the most venomous spider in the world”.
Spiders belonging to the family Pholcidae look very similar to a daddy longlegs (see the picture of a pholcid below)! These spiders (true spiders, belonging to the order Araneae) are called “daddy longlegs spiders” and they do have venom, but this venom is relatively harmless to humans and a bite would be like a bee sting for many people. Pholcid spiders will prey on other spiders which may cause people to assume that pholcids are in turn harmful, or even deadly. So it is possible that the myth originated from something along these lines.
Below are some images showing more of the very colorful and diverse tropical species (first and second images), a species from North Carolina demonstrating the stereotypical temperate species of daddy longlegs, and an example of a pholcid (which is a spider and NOT a daddy longlegs).
The arachnid order Opiliones has several common names in English including daddy longlegs, grand daddy longlegs and harvestmen. I have many wonderful things to share with you regarding the natural history of Opiliones so I’m going to post it in a series of about five posts. Here is the first fun fact to whet your appetite. Keep an eye out for the others very soon!
Longlegs fact #1: Daddy longlegs are NOT spiders.
They are also not insects. So what are they? Well, I’m glad you asked. Daddy longlegs are arachnids belonging to the order Opiliones. The subclass Arachnida includes spiders, scorpions, mites/ticks, daddy longlegs, and several smaller groups, all of which belong to different orders. So daddy longlegs are distantly related to spiders, but are actually more closely related to scorpions!
These incredible arachnids are easily overlooked, as they are most active at night and many species are very secretive in their behavior. Here’s a few examples of species from Costa Rica:
For more arachnid photos see my Arachnid gallery.
This is a fascinating group of spiders, and there’s so much I could tell you about, but I’ll keep it short!
The net-casting spiders belong to a small family (~60 species in 4 genera) of cribellate spiders named Deinopidae – from Greek deinos + opsis, meaning “terrible appearance”. They are distributed worldwide with the majority of species being found in tropical and subtropical regions. Spiders of this family are also often called ogre-faced spiders – I suppose because an ogre’s face also has a fearful appearance. But also because these spiders have an excessively large pair of median eyes while the other six pairs are significantly smaller. Although its creative, honestly I think its a bit of a stretch to say they have a similar appearance to an ogre (but then again, I’m no expert on ogre morphology).
So what is so fascinating about them? Well…
The really remarkable thing about these spiders is their unique behavior for capturing prey! In order to catch prey these spiders spin a web, the “net”, that is held between the first, second and third pairs of legs. The spiders dangle from a strand of silk attached to something above (say, a small branch). Ogre-faced spiders have great night vision with their large pair of eyes. When a suitable prey item, usually some insect, wanders below, the spider drops down, stretches the net and casts it over the unsuspecting prey to ensnare it. Finally, the spider delivers a venomous bite to subdue the prey. Keep in mind that although venomous, these spiders are not considered dangerous to humans!
Check out these great spiders below! Both species were photographed in Costa Rica.
It’s also amazing how these spiders just seem to disappear during the day! They hide under leaves and in dark crevices. But its no surprise how cryptic they can be after you observe one nearly disappearing right in front of you! Accidentally spook them while they’re waiting to capture prey and they will pull all their legs appearing as if they were just a small stick (below). Incredible!
The next time you are outside in your garden or yard and you see a spectacular orb-web, just stop to think about the incredible spider capable of engineering such an intricate design. Look at it very closely. Perhaps you will see a thickened zig-zag pattern in the middle of the web. Or maybe you will notice one very large spider along with a smaller, but nearly identical, spider – a case of sexual size dimorphism, where the male is usually much smaller than the female. Maybe you will even get to witness the spider in the process of building the web!
The orb-web you see was most likely built by a species of spider belonging to the family Araneidae, typical orb-weaving spiders. With over 3,000 described worldwide, the family Araneidae make up the third largest family of spiders after Salticidae (jumping spiders) and Linyphiidae (the sheet web spiders). Araneid spiders are grouped together with other closely related families of orb-weaving spiders in the superfamily Araneoidea. Examples of other orb-weaving families in this group include the Theridiidae (the cobweb spiders; this family includes the widow spiders), Nephilidae (includes the golden silk orb-weavers) and Linyphiidae (sheet web spiders).
Below: A web built between two trees by an orb-weaving spider in Costa Rica.
Some spiders build webs with a very noticeable thickened pattern (zig-zag, circular, spiral, X-shaped) near the center. This structure in the web is called a stabilimentum (seen in the following few photos) and was originally thought to add structural support (i.e., stabilize) the web, but this idea has received little support. The precise function of the stabilimentum is still up for debate, and there are several very good hypotheses each supported by some degree of empirical evidence. The stabilimentum may: help to make the web more visible to larger animals, such as birds birds and mammals, to prevent them from accidentally destroying the web; provide camouflage for the spider; make the spider appear larger; or attract prey species by reflecting ultraviolet light. There are also other theories as to the function. It is highly likely, however, that more than one theory is correct and that perhaps the stabilimentum has evolved to function in more than one way.
Below: Argiope savignyi building a circular stabilimentum, La Selva Biological Station, Costa Rica.
After building the stabilimentum the spider moved to the center of the web and remained still.
It is quite obvious how the stabilimentum in this case makes the spider appear larger as well as camouflages the white body of the spider. If you saw this web from a distance you would also notice how the web is effectively made more visible to our eyes and this might prevent, say, a bird from flying into it.
Below: This stabilimentum is X-shaped and when the spider is at rest its legs also assume this same shape, once again showing that camouflage might be a factor.
Here are some other spiders of the family Araneidae to show the great diversity of this family!
Below: Micrathena sp. from Costa Rica.
These spiders are great to have outside your house and around the garden as they act as a biocontrol, providing a natural way of managing insect populations.
Below: An araneid spider eating an insect, Lafayette, Louisiana, USA.
Below: An araneid spider on a radial line near the edge of the web, Price Lake, North Carolina, USA.
The next time you are outside and see an orb-web take a closer look. And give these fascinating animals some credit!