Carrion beetles like alcohol flux

Let us think for a moment about how many rotting carcasses would be around for a lot longer if not for carrion beetles and their fellow “corpse fauna.”

I thought this was going to be kind of a quick post of some photos of cool insects on tree sap, but then I found out a lot more stuff connected to this seemingly simple event.

I’ve seen carrion beetles in the woods lots of times, on poop or dead things, and I’ve discovered they are very wary beetles. When I approach to try to get photos they quickly scurry to hide under something. But I have developed some sneaking ability over the years from trying to take pictures of things in the woods that don’t want you that close. I think when you have a camera covering your face you register more as a collection of weird shapes, not very threatening, rather than your big two-eyed face moving in. Then all you have to do is not make sudden moves while you try to sneak in as close as you can—although what you think is slow might not be slow to our more sensitive animal friends.

Anyway, I came across a phenomenon: dozens of American Carrion Beetles congregating on a tree afflicted with “alcohol flux.”

American Carrion Beetles congregating on alcohol flux

There’s more than 50 Necrophila americana beetles in that photo (click to view large! Keep zooming!). As soon as I started walking towards them (from more than six feet away!) they started dropping off and diving under leaves. I thought I’d have a little more leeway than that—I was figuring on more like three feet before I had to really start sneaking! I’m going to guess that the ones that remained were too drunk to sense danger.

So. Bacteria and yeasts can get into wounds in trees and start fermenting the sap. Fermentation produces gases which creates pressure which forces the juice out through the wound (called “fluxing”). Depending on which microorganisms and what location inside the tree, this causes a couple different kinds of flux diseases (some are called “bacterial wetwood”). This smelled very strongly of fresh beer, so I’m going with “alcohol flux.” One publication said, “The exudate has a pleasant alcoholic or fermentative odor,” and it really did. They used to try all kinds of things to cure this stuff—flooding it with bleach solutions, drilling holes and inserting drain tubes, etc. Apparently that just prolonged it or made it worse. Now they recommend just leaving it alone, as it isn't really implicated in tree decline.

Necrophila americana beetles, with a few phoretic mites

Wasn’t sure why these meat-eaters would be attracted to alcohol, and while trying to get more info about what carrion beetles do I ended up wandering down the path of forensic entomology, and learned some things I never thought about before. In the first phases of flesh decomposition, when it’s all putrefying and liquifying (and getting stinky), flies are the first visitors. When things die all kinds of exciting chemical reactions start to take place immediately (or stop taking place), and the resulting odor is detected by flies within minutes. They lay eggs, and the larvae eat the flesh.

Were the carrion beetles fooled by the odor and thought there was a flesh-eating party about to start there, or do they simply like fermenting tree juice? They seemed excited. Much congregating!

As close as I could get without scaring them. There's an ant and maybe
a Glischrochilus sap beetle there too.

I've seen the foaming, bubbling version of flux, too, with lots of different species all over it, all quite close to each other—butterflies, ants, bees, wasps, hornets, assorted beetles and flies. They, too, seemed excited (because they were drunk!), lots of darting around and flying about, and ignoring each other and me.

So, I had just assumed that since they’re called “carrion beetles” that they eat carrion, but that’s not quite accurate. Along with learning some of them like rotting fruit, I learned another unexpected thing. What they’re mostly eating on a carcass is the eggs and larvae of the flies that were there first! And they carry phoretic mites around with them, which also eat fly eggs. You can see a few of the mites in the second photo, small tan spots on the beetles (click to view large). Sometimes there’s a whole lot of mites per beetle. And the flies just keep coming and laying more eggs, and the carrion beetles and their mites just keep eating them, and when the carrion beetle eggs finally hatch, the larvae eat some fly eggs and maggots and the flesh that remains because their parents and parent’s friends kept eating the competition. Later the larvae drop off and pupate underground all winter, and there's speculation that maybe some mites go with them? That’s one idea about how the mites end up on the adults—they were with them as pupae.

Different species of carrion beetles like different stuff. Some like snakes, some like feathers, some specialize in reptile eggs (viable or not? I don't know). Some do eat primarily wet flesh, and some like more leathery skin. I have seen them on stinkhorn mushrooms (but they might have been fooled by the smell). Some are attracted to rotting fruit. Still not clear if they're eating it or playing in it.

Then there's the burying beetles…besides what you can see them doing, like dragging a little corpse more than 200 times their weight up to 15’, and excavating the ground underneath it until it’s completely buried, both parents care for the larvae, guarding them and feeding them regurgitated food. Isn’t that nice? That's more than hummingbirds do, and everybody thinks hummingbirds are so cool.

From now on I'll always go investigate trees with weeping wounds to see who's there. I hope to find more carrion beetles and improve my sneaking to get better photos. Carrion beetles! Their larvae eat rotting flesh so you don’t have to!