Can it really be? After so long? Yes, it really can! I invite you to take a moment to distract yourself from whatever emotions you may be feeling about the Iraq Supplemental and learn some more about our friends in the arachnid world!
Today's entry will feature some of my absolute favorite mygalomorph spiders: the trapdoor spiders! And if you want to see previous editions of spider friday and catch up on your arachnid reading, just go to the Spider Friday tag and satisfy your curiosity!
Follow below...
Taxonomy:
Kingdom: Animalia
Phylum: Arthropoda
Class: Arachnida
Order: Araneae
Suborder: Mygalomorphae
Family: Ctenizidae, Barychelidae
Now, first things first: why are they called trapdoor spiders? Well, that one's easy: it's because they live in burrows underneath the ground, and the burrows have a lid with a hinge that acts as a trapdoor. When an unfortunate insect happens to pass by, the trapdoor feels the vibrations of the passing insect, opens the door, snatches it and retreats back to the burrow to enjoy its lunch--all in one lightning quick motion. Case in point: this member of the Barychelidae family, native to Africa. Now, before you watch this video, see if you can identify at all where the trapdoor is! I'll bet you can't...
There are trapdoor spiders spread all over the world--they're found on every continent. And the likelihood is that if you live anywhere in the Southern half of the United States, you've passed right by them and haven't even known. Out here where I live in Southern California, the Bothriocyrtum californicumis found scattered among our hillsides. I know the general vicinity of where to find some around Pasadena, but havent actually ventured out there to go look for them. But if I did and I managed to dig one up, here's what I'd find. (I would reproduce photos, but am unwilling to engage in anything that could be construed as copyright infringement for photos I didn't take.)
As you can see, they resemble other mygalomorph spiders I've written about previously, like the Sydney Funnel-Web, because they share traits common to a lot of mygalomorph spiders (tarantulas included), such as heavy bodies, shape, fang structure, etc. Sometimes, though, trapdoor spiders can be more colorful, as shown by this African Red Trapdoor Spider, Gorgyrella inermis (and damn, do I love YouTube!):
So the question is, what makes a trapdoor spider a trapdoor spider? Well, one could argue that it's the fact that they live in burrows with trapdoors, but the distinction is fluid--a lot of spider, mygalomorphs especially, live in burrows, either with lid coverings or without. But morphologically, what distinguishes a trapdooor of the Ctenizidae family from any other spider is the presence of something called a rastellum on their chelicerae (mouthparts). This so-called rastellum is, in essence, a row of hardened spines that assists the spider in the digging and construction of burrows. The Barychelidae don't have the rastellum, but they're still "trapdoor spiders". From a taxonomic/common name standpoint, there's a lot of overlap: while lots of members of the Barychelidae and other families make trapdoors, not all do. So there's a little bit of confusion as to what actually constitutes a "trapdoor spider."
And from an evolutionary standpoint, these spiders have definitely made themselves comfortable with a burrowing lifestyle. The burrows are lined with strong silk, which not only maintains structural integrity, but also keeps the temperature nice and climate controlled. The lid of the burrow is fused together with more silk from whatever materials--plant, mineral, or otherwise, is close at hand, always so as to make the lid blend in with the natural surroundings. And for many spiders, burrows aren't just one long shaft--they also incorporate other defense mechanisms as well. First and foremost, it can be quite hard for a potential predator like a wasp to open a trapdoor burrow by force: the spide will use its rastellum, its pedipalps and a few pairs of legs to do everything in its power to hold the door shut, and these spiders can be comparatively very strong. But for some spiders who choose flight to fight, defending themselves includes escape routes and other exit shafts:
But the trapdoors spiders of the Cyclocosmia genus actually do that one better: they have a narrowing in the middle of the shaft, and they use a hardened spot on their abdomen to generate a snug-fitting false bottom to make the burrow look abandoned!
Once a female digs a burrow, she'll never leave it unless she absolutely has to, and will continue to expand it throughout her life and she grows with each molt. A male, by contrast, will only leave the burrow to find a mate once he reaches sexual maturity.
MATING:
So here's an interesting question: given the fact that trapdoor burrows are so hard to see, and that a trapdoor spider will attack just about anything that passes by, what is a poor male trapdoor supposed to do about a) finding a mate, and b) not getting eaten if he does? Well, fortunately, biology has just the thing to help with that problem.
First and foremost, male spiders can hone in on females through pheromones emitted by the females. You know, kind of like how you ladies like to wear perfume when you go out. But not getting eaten is another issue entirely. And what many male spiders do is...well...they dance. Just like I mentioned with jumping spiders earlier, male trapdoor spiders approach the burrow with a series of rhythmic tappings of their legs designed to communicate to females that they'd like to be a boyfriend rather than lunch. And if all goes well, the female will emerge, and the male will lift her up and transfer sperm to a specialized spot on her abdomen, called the epigastric furrow, using the emboli on his pedipalps. And again, here's why I love YouTube--here are parts 1 and 2 of a successful mating between a loving arachnid couple in the Barychelidae family:
Subtropical species mate in the summer, but tropical species can breed year-round, depending on the cycle. After mating, the female will lay eggs in the burrow, and the spiderlings will stay in the burrow for a little while after hatching. The mom will feed them with excess prey she captures until they are ready to disperse and dig their own burrows, beginning the cycle anew.
Hope you enjoyed spider friday! I'll hope to see you next week with even more spiders! If you'd like to request a particular spider, please leave it in the comments...