Biodiversity & Evolution

Archive for July, 2012

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!

http://www.savethefrogs.com/

http://www.amphibianark.org/the-crisis/chytrid-fungus/

http://www.amphibians.org/