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
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!
danielproud 