Hi all, and welcome to yet another edition of Spider Friday--your once-a-week chance to take a minor break from politics and explore the realm of your eight-legged friends.
I received a lot of wonderful suggestions for featured spiders in my post yesterday--Argiope, solifugids, and a few others. Really, I'm intending on getting to all of those, because they're wonderful suggestions.
Right now, though, I'm going to touch on a subject that really touches on just how amazingly adaptive nature can be: ant mimicry among spiders. Yes, there are spiders that look and act like ants because it suits their devious conveniences, and some take the act a lot farther than others!
Now, the first spider I'm going to introduce you to is a jumping spider--a bona fide member of the salticidae family. Now, I'm sure you remember from previous entries in the Spider Friday series what jumping spiders tend to look like. Compact bodies, short, stocky legs. Fuzzy, and actually kind of cute. Something kind of like this:
Well, allow me to introduce you to Myrmarachne plataleoides, the Kerengga Ant-like Jumping Spider native to Southeast Asia:
Is that uncanny or what? Not surprising: Myrmarachne comes from the Greek "Myrmex" (ant) and "Arachne" (spider).
Now, before I go further, some morphological notes are in order. You see, there are two main morphological factors that differentiate insects from spiders. The first, of course, is the number of legs. If it has more than six legs, it's not an insect. Spiders obviously have eight. But getting a little more technical, another key morphological difference is that all insects have three--and only three--body segments: a head, a thorax, and an abdomen. A spider only has two--a fused cephalothorax (head/thorax combination) and an abdomen. So take a look at that picture one more time!
If you look closely, there are still only two body sections, with a pretty clear segmentation between them--but the cephalothorax narrows to create a false distinction. In addition, look at the eyes. Clearly visible on the sides of the head, right?
WRONG!
What have I always told you about spiders? That's right--you can tell what they are by looking at their eyes. And if you remember what I told you about jumping spiders last year, then you'll remember that jumping spiders have four large eyes in front, with two sets of two smaller eyes higher up on the carapace. And indeed, if you look at M. plataleoides from a different angle (the one below is a male), you can see exactly that:
So what are those other "eyes"? Absolutely nothing! Just part of the disguise to make the spider look more like an ant--they serve no other purpose! But for M. plataleoides and many other spiders of the genus, the disguise is based on far more than appearance.
Now, you may have noticed that the male pictued immediately above has massive chelicerae (jaws). Yep--that's a secondary sex characteristic for male spiders of the species. See, since spiders are typically so female-dominated with regard to sexual courtship, you don't tend to ever think that there would be grudge matches between male spiders like there are between, say, deer, or lions, or stag beetles. But among these jumping spiders, the males will duke it out using those oversized chelicerae the way deer use antlers.
These spiders will also mimic ant behavior at a superficial level by walking with their front legs outstretched as imitation antennae to fit better into the ant world, who use antenna contact as a means of social communication.
So at this point, the question is: if you're a spider, what advantage is it to you to look like an ant?
Well, if you're the Kerengga spider described above, it's all about protection. The Kerengga spider hangs out around colonies of the ant is tries to imitate--the Weaver Ant. Now, weaver ants have dangerous stings and taste bad, primarily because like all ants, they produce and contain formic acid. So, by hanging around the Weaver ant colonies, the spider, which would otherwise make for a tasty snack for birds and other predators, gets to enjoy the protection that goes along with being taken for a member of the Weaver colony, and gets to live in a little less fear of being eaten.
Now, if you're M. plataleoides, you have the decency and the intelligence not to try to eat the ants you're imitating. But there's a whole genus of ant-mimic spiders that takes this whole deception game just a little past the grounds of common courtesy.
Meet the members of the Habronestes genus (click on link to view photos).
They don't look as much like ants as Myrmarachne does--but what they lack in looks, they make up for in behavior. These spiders will actually use their disguises to eat members of the colonies they're hiding in. Yes, they'll use their legs like antennae, but the Habronestes do one better: if they kill an ant, they can actually use the ant they just killed to fit better into the colony! See, if they've just killed an ant, and another ant "asks for identification", as it were, the Habronestes can just present the ant she just killed to the other ant, and the ant will assume that the spider is merely just another worker ant carrying a deceased fellow ant to the garbage pile.
In concluding, let me leave you with one more shot of a spider from the Myrmarachne genus, clearly showing all the ant-mimic features, as well as the telltale Salticidae eye arrangement:
Hope you enjoyed Spider Friday! I'll be back next week with even more spidery goodness.