Part IV: Chemical Defenses of Harvestmen
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.
A species of Cosmetidae using its chemical defenses. The yellow droplet seen on the legs was first produced from the glands on the body and then transferred to the legs. A clear droplet can be seen on the body between legs I and II (on the right side).
Eupoecilaema magnum (Cosmetidae), one of the largest cosmetids, from La Selva Biological Station, Costa Rica.
Another species of the family Cosmetidae. There are over 700 species just in this one family!
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.
Part III: How many species of daddy longlegs?
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.
Meterginus inermipes (Cosmetidae) from Costa Rica
Cynortellana oculata (Cosmetidae) from Costa Rica
Unknown species, likely a new species, of Cosmetidae
Prionostemma sp. (Sclerosomatidae) from Costa Rica
Part II: Truth about daddy longlegs
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).
Cynorta annulata, Costa Rica
Undescribed species of Cosmetidae, Costa Rica
Leiobunum vittatum, North Carolina
A spider belonging to the family Pholcidae. It is often confused with true daddy longlegs (Opiliones).
The truth about 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:
Prionostemma sp. feasting upon what remains of an insect
Cynorta marginalis eating an earthworm as a second individual sneaks up.
Poecilaemula signata (male) with enlarged chelicerae
The orange harvestman, an undescribed species
For more arachnid photos see my Arachnid gallery.
Appalachian Golden Hour
Since I moved about 6 weeks ago, I have been exploring some new great locations to photograph the sunrise and sunset here in the Appalachian Mountains of western North Carolina. Yesterday, I found a great spot for both the sunrise and sunset and I was lucky enough to have something more than a grey, overcast sky (as lately it seems there is a 50% chance of rain all day, every day). I hope to continue this series of posts as I discover more great places to photograph the landscape here in the High Country of North Carolina.
Sunrise on Blue Ridge Parkway
Above: A view of the sunrise from an overlook along the Blue Ridge Parkway in North Carolina.
Sunset in Boone, North Carolina
In addition to capturing some nice colors in the sky, I also took a few nice macros of a bumblebee on a thistle with a red sky in the background. With and without flash.
Bumblebee on a thistle
Silhouette of a thistle with bumblebee
Mushroom Forest
This is one of my personal favorites of all my macro shots. These tiny mushrooms were such a lucky find. When I realized how great the shots turned out I wanted to go back and try out some other camera settings. But by the time I returned the following day all of the mushrooms had been eaten. Location: Las Brisas Nature Reserve, near Turrialba, Costa Rica, July 2011.
I entered this photo in the “Art of Nature” photo contest at PhoozL.
Photo caption: From an insect’s viewpoint these mushrooms tower above creating a mystical landscape.
Mushroom Forest
Red-Eyed Tree Frog
I love photographing herps! Especially the Red-Eyed Tree Frog of Central America. This frog is so photogenic that it is difficult to take a bad picture of these spectacular animals! These frogs are commonly represented as the face of conservation efforts to save the rainforest. Many frogs (and other amphibians) are rapidly becoming endangered because of habitat loss as well as the spread of a deadly chytrid fungus called Bd. See below for links to more information.
I recently submitted this photo to the “Art of Nature” photo contest on PhoozL.com . Click the first image below and it will take you to the PhoozL gallery for the contest. Its free to enter, so submit your own photos!
Here are some of my other favorites. I just never get tired of seeing these amazing frogs!
Here’s some links in case you are interested in learning more!
Ogre-faced spiders
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!
Orb-Weaving Spiders
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!
Astonishing diversity of longhorn beetles
The other evening as I sat in the living room with the porch door open I heard an insect flying around outside the screen door. I knew it had to be quite large just based on the sound. I went outside to investigate and found a monstrous longhorn beetle on the screen. I picked it up and put it in a container to keep it alive until morning when I could examine it more closely and take photographs under better light. Attached are some shots of the beetle from Boone, NC, along with some pictures I had taken over the years of three species from Costa Rica, and some general information on longhorn beetles.
The longhorn beetles are part of the insect order Coleoptera which includes all of the beetles and is the most diverse order representing about 20% of all described species of animals! However, there are still many more species that have yet to be discovered! Within Coleoptera, longhorn beetles belong to the family Cerambycidae. This family has roughly 20,000 species worldwide and about 9,000 in the western hemisphere (see Larry Bezark’s Photographic Catalog of the Cerambycidae of the World). You can see the great diversity of this family for yourself if you look through some of the photos on BugGuide.net. Needless to say, since I am no expert on cerambycids, this makes a positive identification of the species I photographed quite difficult. My best guess is Knulliana cincta (Banded Hickory borer), but several species look very similar and are differentiated based on body size, spines of the antennae and legs, and other minute details. For example, compare it to the species Parelaphidion aspersum. So you can see the difficulty in identifying something to species level for a non-specialist, and sometimes even for expert taxonomists! So I welcome any comments from anyone with insight on the species identifications of any of these cerambycids.
The common name “longhorn beetle” comes from the fact that many species have antennae that are as long as or longer than the body. The species photographed here was more than 2.5 cm in length and the antennae were more than twice the length of the body! However, some species may be quite small (less than 1 cm) and the antennae are not always longer than the body.
Many species are cryptically colored as shown above. Its incredible how well this organism is camouflaged on the trees! Consider that he would be even more well camouflaged if my flash hadn’t cast a shadow! Other species are quite colorful such as this one from Costa Rica (below).
Acrocinus longimanus (Cerambycidae)
Below are two more relatively large species that were photographed at La Selva Biological Station, Costa Rica in 2009 (prior to having a macro lens). This individual here was found inside of a dead palm frond and was photographed on the smooth shiny surface of the bare palm tree for contrast.
Derobrachus sp. (Cerambycidae)
The specimen show below was found on a wooden window frame at the research station in Costa Rica.
Callipogon marechali (Cerambycidae)
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