Pondering an earwig mystery...

Yesterday, I watched an Acorn Woodpecker land on one of the smaller Olive trees in front of my house (trunk diameter = 4 to 5 inches). It was pecking, probing, and intently feeding on something in a depression in the trunk. I suspected termites of some kind, but after viewing the action through binocular for several minutes I realized that it was pulling out earwigs! I must have watched it pull out at least 10 wriggling (seemingly adult-sized) earwigs using its forcep-like bill in the span of about 5 minutes. I went outside later to get a look at where it had been feeding. About 4 feet off the ground, there was a small (natural?) cavity in the bark which seemed to extend fairly deeply into the trunk of the tree.

Here's my question: What would so many earwigs be doing in this location? I was under the impression that adults would typically be found under leaf-litter or on low-lying vegetation and that their eggs/young were hatched and raised in the soil. Has anyone ever observed them inhabiting crevices in trees before? Can anyone think of a credible hypothesis for what I observed?

Contributed by Harsi S. Parker on 2 October, 2009 - 1:28pm

Thanks to everyone for their input!

I honestly never expected so many responses. Thanks to your comments, I think I have been sufficiently disabused of the notion that earwigs are primarily found close to the ground, though it's still a bit of a mystery to me what so many of them were doing packed into that small hole in the tree...

[Abigail -- Did you receive the e-mail I sent you yesterday? Let me know via e-mail if you never got it.]

… Harsi S. Parker, 10 October, 2009 - 2:22pm

not unusual

Earwigs on trees, houses, walls, etc. is not unusual; especially European earwigs. I have observed earwigs several stories off the ground on hotel walls. I have found a dozen earwigs (Anisolabis maritima) under the same piece of wood along beaches. There is a tree in my area where you can pick 50 European earwigs from the leaves a night.

… wolfpacksved, 6 October, 2009 - 2:07pm

Just a guess

You say that you didn't take a close look at the "earwigs". Could they have been staphylinids? I know that I could easily mistake them at a distance.

… Beatriz Moisset, 3 October, 2009 - 8:24am

This is my husband's theory too...

When I told him about what I saw, (being a very rational sort of guy) the first thing he said was -- [Are you sure they were actually earwigs?

Well, I felt pretty certain at the time, but there's always a chance my eyes were playing tricks on me. I tried to take some images, but they were through my kitchen window and the woodpecker was gulping the insects down pretty quickly once they were removed from the tree. Nevertheless, I just posted to the Frass section the single (very bad) image I managed to get. So those who want to squint at it and tell me if they think it looks like the back-end of an earwig -- click here!

… Harsi S. Parker, 6 October, 2009 - 6:51pm

nice woodpecker!

That does look like an earwig's cerci, but I know very little about the insects. I do know a bunch about birds, and I envy you your backyard acorn woodpecker! - they're so appealing with their small size and clown-face markings.

… Abigail Parker, 9 October, 2009 - 7:44am

Another aggregation

I wonder how many species have the habit of joining in big aggregations. This is a little off topic but it has intrigued me for a long time. I saw Opiliones in Mexico gathered by the thousand in rock or tree crevices. Eventually I read that they seek shelter from the heat and dryness and come out at night to feed.
This picture was taken in the Sierra Madre and I am sure that there must be similar aggregations in Texas or New Mexico; but so far, nobody has submitted something similar to Bugguide, as far as I know.

… Beatriz Moisset, 2 October, 2009 - 6:34pm

Thanks for the input, guys!

Interesting comments from both of you. (Scott, if only I could chalk it up to recent rainfall, that would be wonderful! Sadly, southern California persists in its ongoing drought...)

It's not so much that they were above ground which has me scratching my head, it's that they seem to be inhabiting the inner recesses of the tree itself. And not just one or two... Like I said, I saw that woodpecker pull out at least ten. I just went back outside to get a closer look at the crevice and it is actually more like 5 feet off the ground and the accessible, shallow area at the opening is small enough that it couldn't feasibly hold that many earwigs. Which means, as I suspected, that the woodpecker must have in fact been using its long bill (and even longer, probing tongue) to extract them from much deeper in the heart of the trunk itself. Weird, eh?

… Harsi S. Parker, 2 October, 2009 - 3:39pm

Not just ground-based

Some species are almost always only found under tree bark. The native southwestern species tend to live mostly in rotting cactus.

The critical factor is shelter and protection from desiccation. In a dry climate like southern California, there are few places on the ground that aren't bone-dry this time of year (with the exception of irrigated plantings, of course). I would suspect that the earwigs survive by hiding under bark during the day, then coming out at night when the temperature drops and the relative humidity rises.

… Chuck Entz, 2 October, 2009 - 4:53pm

This tree is young enough that its bark is still quite smooth...

...so there wouldn't really be an places to hide in that manner. As I mentioned, they seemed to be inhabiting a small naturally-formed (or possibly excavated) hole in the trunk of the tree. Regardless, your theory regarding the need to seek moisture and shelter from the elements is still quite valid and plausible. Thanks!

… Harsi S. Parker, 6 October, 2009 - 6:44pm

Earwigs aboveground

I often find European earwigs tucked into crevices of herbaceous plants, a few feet above the ground. I just checked my files and I have a shot of four clustered at the top of a milkweed plant. No idea what they're doing there though!

… Charley Eiseman, 2 October, 2009 - 2:51pm

Here's a picture of one I fou

Here's a picture of one I found on a milkweed plant in a park along Chicago's lakefront.

http://insectsofthechicagoarea.blogspot.com/2009/08/earwig.html

… Gary J Sibio, 9 October, 2009 - 3:03am

I have seen...

European earwigs in many locations above ground. I thought they were seeking higher ground from recent heavy rainfall. I even found one floating in a fresh (covered) cup of black coffee :^P. Luckily, I checked the cup before I took the first sip.

I find them in my mailbox on occasion.

… Scott Justis, 2 October, 2009 - 3:22pm

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