Ant-Mimic Jumping Spider
While coming up the hill on my way home from work[1], I spotted what looked, at first, like a medium-sized ant. It didn’t look quite right, though, so I caught it and brought it home. It turned out to be this:
It’s a jumping spider that mimics an ant[2]. It’s about the size of the Formica ants we have around here and looks a lot like them. The mimicry extended to its behavior, too. While I was catching it, it pointed its abdomen at me in a threatening sort of way. This is the same pose the ants take when they are annoyed, just before they spray formic acid. So, any predator that had a previous run-in with a Formica ant is likely to assume it’s about to suddenly get another facefull of acid, and beat a retreat. The mimicry is a nice, neat solution to predation for the spider, that works OK for as long as the ants are a lot more common than the spiders.
You can see how much the abdomen looks like the abdomen of an ant here. It even has white lines across it to simulate a segmented abdomen, because ant abdomens are visibly segmented but spider abdomens aren’t:
The coloration is pretty similar to the Formica ants, with a black abdomen and the rest of the body dark red. The mimicry falls apart at the head end, which doesn’t look all that ant-like, but that probably doesn’t matter so much. An attacking predator is going to be confronted by the abdomen, and probably won’t even see the head.
I wanted to get some pictures of the face so we could see the eyes, but like a lot of spiders it has the annoying habit of scrunching down with its legs arched over the face. It didn’t want to move, so I tried nudging it a bit with a toothpick to get it to reposition the legs. Unfortunately, this prompted it to suddenly leap out of the dish, dash across the table, and leap off into the nearby bookshelves. It got away clean, after I’d only gotten five pictures. Normally, I have to take about 20 to 40 pictures to get a few that show the details I want to see, so I didn’t get anywhere near as many as I would have liked this time. Without pictures of the eyes, it’s only a guess that it is an “antlike jumping spider”, subfamily Synagelinae. On the plus side, it did confirm that it had pretty substantial jumping abilities, so some species of jumping spider seems pretty likely.
I gather that there are two reasons for spiders to mimic ants. The obvious one is to convince predators that can’t really deal with ants that they won’t be able to deal with the spiders, either, and so leave them alone. The other reason is a bit more insidious: if the ants buy the mimicry, then the spider can sneak up on unsuspecting ants and pounce on them while the ant thinks that they are another nestmate. This usually requires that the spider also emit some scent cues so that they will “smell right”. If it does this well enough, it might even be able to sneak into the nest and feast heartily. I don’t know if this one is a good enough mimic to fool the ants, though. It might just be getting by with giving predators the idea that it’s more dangerous than it actually is, and leaving the ants alone. I’ll have to seriously watch some of our Formica nests to see if there are any ant-mimic spiders hanging around them.
——–
[1] I bicycle to and from work once the show melts, but the last half-mile to our house is really steep (it’s one of those hills that has signs saying “Trucks Use Low Gear”, and I think it’s a 12% grade in some spots). I can ride the bike up the hill, but it wipes me out. So, I push it up, which means I am walking slowly up the hill leaning forward, and can easily scan the paved shoulder to look for interesting critters.
[2] Although, as ant-mimic spiders go, this one isn’t anywhere near as impressive as some others. The one that gets me is this one, where the male spiders actually have turned their mouthparts into a second fake ant, so they are mimicking an ant carrying another ant.
Leave a comment