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|
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”). Since this one smelled very strongly of fresh beer, I’m going with “alcohol flux.” One publication said, “The exudate has a pleasant alcoholic or fermentative odor,” and it 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|
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.
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 they 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 already there! 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 with 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 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!