Hello again all you science and spider fans! Welcome back to Spider Friday! (see other Spider Friday entries
here.)
I'm pleased to report that the Spidiaries are back after a week's absence due to wandering around on 90 minutes' sleep walking like zombies up to grassroots luminaries and asking for pictures at DemocracyFest in San Diego. Now that that is over with, I am able to return to my regular weekly Spiderfest.
So, without further ado, I bring you: the Netcasting Spider!
TAXONOMY:
Kingdom: Animalia (Animals)
Phylum: Arthropoda (Arthropods)
Class: Arachnida (Arachnids)
Order: Araneae (Spiders)
Suborder: Araneomorphae (true spiders)
Family: Deinopidae (Deinopid orbweavers)
As Rumsfeld would say, there are the spiders you know that you know. These are the known known spiders. Black widows, things like that. Then there are the spiders you know you don't know--like, whatever enormous theraphosid happens to be sitting in a jungle in the middle of Borneo somewhere. Then there are the spiders you don't know you don't know about. They're the unknown unknown spiders.
Now, I'm not exactly sure what spiders those would be. Maybe some extraterrestrial giant arachnids from War of the Worlds or something. But anyway, let's take a known unknown and turn it into a known known, shall we?
BACKGROUND:
The "Net-casting spider" doesn't refer to just one different spider. There are a whole slew of netcasting spiders out there, but all of them are within the Deinopid Family of orbweaving spiders.
Now, the mere fact that a spider is in the orbweaver family doesn't mean that it spins nice, pretty geometrical webs every night. The bolas spider, for instance, belongs to the other orbweaving family--the Araneidae--but weaves a prey-catching web that is anything but traditional.
So, back to Net-casting Spiders. Within the Deinopidae family, there are four different genera: Avellopsis, Menneus, Subrufa, and Deinopis. For the sake of this treatment, I'll select the Deinopis genus--commonly called the "ogre-faced spiders"--as they are the most common and widely distributed Net-casting spiders. These spiders are generally earth-colored, elongated stick-like spiders whose legs are situated to form an X-pattern at reest.
So, what makes Net-casting spiders unique? Well, when most people think of spiders, they tend to think of them in two categories: spiders that just wait for insects to come to their web--orbweavers, wolf spiders and the like--and spiders that don't use silk to hunt--tarantulas, recluses and the like.
Well, the Net-casting Spider introduces a third category: spiders that bring their web to the prey. You see, net-casting spiders weave a fine, blue-tinted expandable net of cribellate silk--the same type of "dry adhesive" silk used by black widows and common house spiders:
(image from the Wikipedia commons)
The spider will then sometimes--depending on the species of spider in question--put a drop of white fecal material on a leaf or other item below the spider to serve as a target, and hang upside-down over the target with its net suspended between its two front legs:
(image from Brisbane Weavers)
The spider will wait for prey to pass by, and in an instant, snare the prey using the net and bite it before it can wriggle out--kind of like one of those retiarius gladiators I used to read about in my former like as a academic classicist. These spiders generally start spinning their web late in the day, hunt at night, and then either eat or discard the web in the morning.
So, let's talk a little more about the Deinopis spiders.
RANGE:
They are nearly exclusively found in the Southern Hemisphere, for one thing. Australia and Africa have a whole ton of them. There is only one Deinopis spider found in the United States, and that is D. spinosus, located in Florida (which may as well be in the Southern Hemisphere anyway). D. subrufa is a common photograph subject in Australia, especially the region around Brisbane, where they are very common. This map, again from Wikipedia commons, shows the areas in which you might find a particular species from the four genera of Net-casting Spiders:
Southern California is listed here, but I myself have never observed a net-casting spider in the wild. It would be a real treat, though.
MORPHOLOGY:
Anyone who has read my previous Spidiaries know that I am really into the various eye arrangements of different spiders. The Deinopid spiders prove that my interest is justified. You see, the Deinopid spider hunts insects by snagging them at night in low light with exact precision. And to be able to do that, it needs an eye structure that's suitable to the task.
And they have one. Deinopid spiders are commonly called "ogre-faced spiders because of their unique facial features--unique among spiders, anyway. They have two very large forward-facing eyes that are excellent for low-light visibility--and the rest of the eyes are simply afterthoughts:
(Photo from Ski.org
Even to a regular observer without a nice close-up ability, this facial shape is pretty remarkable:
Now, to my mind, this co-evolution is fascinating--because if you're going to try to hunt insects at night in low light, the only thing that will really do is large-eye stereo vision. Don't believe me? Well, check out this bushbaby for comparison--and forgive the animation:
And don't even get me started on the owl. And no, when I said "bushbaby" I wasn't referring to this:
REPRODUCTION:
There are a whole bunch of different netcasting spiders out there, and reproduction among net-casting spiders isn't really all that groundbreaking or shocking. There are a few things worth mentioning, though. Australia, for instance, always has something weird to recommend for itself.
In D. subrufa, the most common net-casting spider in Australia, the males are actually larger than the females, even though they have narrower abdomens because they don't need all that egg-making equipment (no, ladies, this is not an excuse to start complaining. In many spider species, the guy still gets eaten, okay?).
Among most net-casting spider species, egg sacs are usually round and brown. Here's a nice photo of D. subrufa actually making an egg sac:
So, that ends my treatment of net-casting spiders. I'm sorry it had to be so vague, but there are a lot of them out there so I had to speak in general terms.
Before I take my leave, however, I would like to end with one more example of why being a male human is a far better life than being a male spider. Like I've said before, we may be ignored, rejected, or just totally fail to pick up on signals. But chances are, we'll survive. We don't have to deal with this.
And with that, I must go take a minute to find a bug for Emily. I'll see you for next week's...SPIDER FRIDAY!