Evolutionary Biologist and Nature Photographer

Arachnid

The green harvestman!

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.

Prionostemma sp. "verde" - The green harvestman

Prionostemma sp. “verde” – The green harvestman


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.


Arachnologists Unite

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.

A small juvenile, female Dolomedes tenebrosus (Pisauridae).

This spider appears to have placed its egg sac into what’s left of this dead plant.

The always charismatic jumping spider, Phidippus sp. (Salticidae)


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).