Previous Spider Fridays:
5/26: The Brown Recluse
5/19: The Sydney Funnel-Web
5/12: The Black Widow
Hello Kossacks, and welcome to yet another edition of Spider Friday--for on the seventh day, God actually created spiders--it's just that She has so much fun doing it that She called it rest.
This week we'll be taking a look at the Bolas Spider--one in an irregular sub-series I intend to do concerning spiders with "alternative" hunting methodologies.
So follow me below the fold for more.
TAXONOMY:
Kingdom: Animalia (Animals)
Phylum: Arthropoda (Arthropods)
Class: Arachnida (Arachnids)
Order: Araneae (Spiders)
Infraorder: Araneomorphae (True Spiders)
Family: Araneidae (Orbweavers)
Subfamily: Mastophoreae (Bolas Spiders)
Genus: Mastophora (American Bolas), Cladomelea (African Bolas), Ordgarius (Australian Bolas)
BACKGROUND:
Bolas spiders have worldwide distribution (except Europe), with three different genera depending on location, as shown above. Bolas spiders are quite small--usually no more than 15mm at their largest--and are strangely shaped, with bulbous, irregular abdomens, sometimes featuring knobs of varing shapes:
(M. cornigera, found in California)
Bolas spiders hunt moths through trickery--more on that shortly--and some bolas species enhance the effect through "eye spots" on their abdomens, which make them resemble the moths they hunt:
(O. magnificus, the Australian Magnificent Bolas)
So what makes Bolas spiders unique? Well, all spiders hunt by either either stealth or by trapping their prey in silk--or some combination of the above, with interesting variations that I'll touch on in subsequent weeks. All spiders, that is, except the Bolas.
The Bolas spiders hunt by chemical mimicry, in addition to silk. Despite their genetic presence in the Araneidae family of orbweb weavers, bolas spiders get their name because they will hang upside-down dangling a sticky ball of silk from one of their legs, like so:
(American Bolas, M. hutchinsoni)
or so:
(African Bolas, C. longipes)
or so:
(M. cornigera)
Now, that may not seem like a very effective hunting technique--until you understand that these little balls of silk are laced with female moth pheromones produced by the spider. Now, moths are able to reproduce because male moths can detect female moth pheromones at a rate of a couple of parts per million in the air, and they're instantly drawn to it.
The bolas spider will lie there and wave the sticky ball of pheromones back and forth to waft the scent into the air. When a poor unsuspecting moth comes by--thinking he's going to get a mate--the spider will then throw the "bola" like a lassoo faster than the human eye can see, and will hit the moth with the sticky ball with uncanny accuracy:
The spider will then wrap up its prey in silk to save for later, or consume immediately if it's hungry.
BUT HERE'S THE KICKER: Bolas spiders are extremely specialized; each moth species produces a different pheromone, and bolas spiders produce the specific pheromones for the specific moth species on which they predate. So if you took an American bola spider to Australia, or vice versa, the spiders would starve. But it gets better: some species of bolas spiders even have the ability to customize their pheromone output depending on food availability.
Let's take the case of the American Bolas Spider, M. hutchinsoni. This species hunts two different types of moths: one moth is active from the early evening until 10:30pm, but the other species is active only after 11:00pm. A study by K.F. Haynes of Kentucky U. did a study analyzing the dietary patterns of M. hutchinsoni and came up with some amazing results: the spider produces a mix of both moth pheromones early in the evening because the moth that is active early isn't repulsed by the pheromone of the moth that is active later, but since the moth that is active later is repulsed by the pheromone of the moth that is active earlier, the spider will shut down production of the pheromone of the earlier moth as the night goes on!
This degree of specialization--and the concept of exactly how these spiders manage to mimic the pheromones of all these different moths exactly--is kind of mindboggling. In fact, it's no accident that I made mention of God creating spiders above the fold. Lots of creationists--and not just Christians--use the bolas spider and other spiders as evidence of the difficulties of the evolutionary model.
BITES:
The bolas spider is only dangerous to your local moth, or whatever other insect just happened to fly into the neighborhood--bolas spiders see very well, and will attempt to lasso any bugs that fly by. No complications from bolas have ever been reported.
LIFECYCLE:
Bolas spiders aren't just strange in the way they hunt. Their reproductive cycle is also a little on the strange side.
Bolas spiders mate late in summer. In late fall, the female's abdomen will swell much larger than it usually is, and she will produce egg sacs suspended from a retreat, each one usually containing a few hundred eggs:
(M. cornigera)
The egg sacs of O. magnificus are much larger than the spider herself:
Depending on the climate and the species, the adult female may or may not die out over the winter. The spiderlings, however, will ride the winter out in the egg sacs, and emerge in late winter or early spring for the cycle to begin anew.
So what's so bizarre about this? Well, the sexual dimorphism, for one thing. Males are so small (1-2 mm) that they are seldom observed, and because of that, bolas spider mating is an extremely rare sight. But in addition, male bolas spiders emerge from the egg sac ready to mate! The vast majority of spiders have to go through at least a couple of months of maturing, and females and males generally mature at the same time--but not these guys.
Want to get a feel for how small these males are? Well, here's an adult male M. cornigera who has just emerged from his egg sac--the egg sac is one of the ones in the above photo of M. cornigera egg sacs:
And that should just about do it for the bolas spider! I'm not sure what's going to happen next week, since I'll be in Yearly Kos--but I'll try to do some spider blogging from Las Vegas if at all possible.
