My, what big eyes you have!
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!
Caddo pepperella (Caddidae), from Wisconsin
Caddo pepperella (Caddidae), from Wisconsin
Updated on 4/2/13 – species is Caddo pepperella, ID by J. Shultz.
The Harvestman with Horns
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.
Male Phalangium opilio Linnaeus 1758.
Image below: Same male, dors0lateral view.
Male Phalangium opilio Linnaeus 1758.
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.
Female Phalangium opilio Linnaeus 1758 demonstrating the lack of cheliceral horns and smaller pedipalps. Dorsal view.
Female Phalangium opilio Linnaeus 1758 demonstrating the lack of cheliceral horns and smaller pedipalps. Lateral view.
References:
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.
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.
danielproud 