Ant Nest in Hollow Apple Tree
We have some very elderly apple trees in our yard, and one in particular is pretty thoroughly hollowed out. Starting last year, we started noticing that the hollow part was getting stuffed with a mixture of dry grass and wood chips. Here’s what it looked like by June 29, 2014:
On closer examination, we could see that there were ants living in it.
And then we remembered that late in the previous summer, we’d been seeing ants carrying bits of debris up the side of that particular apple tree. Ants like these:
They were red ones with black abdomens, which tend to be in the genus Formica. This is also the genus that tends to build nests out of “thatch” like this.
They were also patrolling all over the tree in general. We often see ants of this type “farming” aphids, and they will also attack and eat things like caterpillars.
They were pretty vigorous about defending their tree, too. This one decided she was going to take on the giant finger-monster singlehandedly.
This is incidentally one of the ways that Alex Wild recommended to get ants to stay still long enough for a good picture (“#6: The Angry Ant Trick”). Ants are really prone to scurrying so much as to make photography difficult, unless they are either eating/drinking or trying to kill something.
These look a great deal like some that we spotted previously tending scale insects on a tree in our yard, which were tenatively identified as most likely Formica obscuriventris. This elevated nest in a hollow tree seems a bit atypical, they evidently are more likely to build their nests under partially-elevated rocks or logs, with thatch stuffing to fill crevices.
A few weeks after taking these pictures, I noticed several bluejays in the tree behaving oddly. They would poke around at the thatch a bit, and then stand on it with their feathers a bit fluffed out and their wings a bit out from their bodies. I think they were “anting”, letting the ants run all over them, biting their feathers and spraying formic acid. While there is no question that birds do this, there are arguments about exactly what they are trying to accomplish by it. It’s possible that the ants are killing mites and parasites, and the formic acid sprays could be antibacterial/antifungal. Or they might just be scratching where it itches. It has also been suggested that some birds (and bluejays in particular) might be waiting for the ants to empty out their formic acid glands, and once the ants are drained and harmless the bird can pick them off and eat them. In any case, after this episode the nest was pretty much destroyed and the ants were gone.
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Fascinating. I’ve seen blue jays anting, but never noticed them destroying an ant nest. Armadillos get into our fire ant nests looking for the grubs, but I don’t believe they can climb.
Sadly, Argentine ants have wiped out most of our native ants here in San Diego. They’re so tiny that the ant predators don’t eat them. They also don’t fight when they meet Argentinians from other nests. Instead, as far as I can recall, they cooperate.