Excerpts from Jim Conrad's
Naturalist Newsletter

Entry from field notes dated June 21, 2023, issued from near Tequisquiapan, elevation about 1,900m (6200 ft), Querétaro state, MÉXICO (~N20.57°, ~W99.89°)
LINED EARWIG

Lined Earwig, DORU TAENIATUM

On the limewashed wall of an outdoor toilet, the above earwig perched unmoving for a long time, just occasionally quivering its antennae. With "pincers," or cerci, protruding from the rear end of a narrow body with long, slender antenna, it was an earwig, and nothing else.

However, in the Earwig Family, the Forficulidae, nearly 500 earwig species are recognized, in more than 70 genera, most of them looking pretty much like earwigs. In such cases, GBIF's Forficulidae page comes in handy. On the map, zoom into our upland central Mexican area, click "explore," and you see a couple of pages listing all the earwig observations in the region. Four species are represented, each in a different genus. By making image searches on each species, it soon becomes clear that our toilet visitor is the Lined Earwig, DORU TAENIATUM.

Lined Earwigs are native American, occurring from the southern US and Mexico south to about southern Brazil. They're fairly similar to the better known Common Earwigs, Forficula auricularia, which are native to Eurasia and probably North Africa, but invasive throughout much of North America, as well as New Zealand and probably elsewhere.

When you see an earwig, two main questions come to mind: Can the "tweezers" at the rear end "bite," and; How can this insect fly with such stubby wings?

With regard to the rear end, it can pinch, but only weakly, and can't hurt humans. However, earwigs can emit a disagreeable-smelling, yellowish-brown liquid when feeling threatened. By the way, the pincers of females are straight-sided, while on males they're strongly curved, so ours is a male.

Understanding how such short wings can enable an earwig to fly starts with recognizing that earwigs bear four wings -- two forewings and two hindwings. Also, it's the hind ones mostly involved in flying, even though in our picture the hind wings appear to be much shorter than the front ones.

In our picture, what appear to be longer forewings actually are oblong, leathery plates extending down over the hindwings. When earwigs want to fly, a very thin membrane expands like a fan from beneath the striped leathery coverings. But, it's more complicated than that.

The insect bends its rear-end up over its back and uses its pincers to unfold its wings, one at a time. This is a somewhat time-consuming process without parallel in the rest of the insect world. The procedure is photographed and explained in the 2002 work by Fabian Haas entitled "The evolution of wing folding and flight in the Dermaptera (Insecta)." There it's explained that "... the fore wings cover the hind wings and so the latter have an extra layer of protection by the fore wings." Once the wings are unfolded, they do a good job. Earwigs have been reported accumulating around night lights in the tropics by the thousands.

Is our Lined Earwig good or bad? In the 2010 study by Mabel Romero Sueldo and others entitled "Characterization of the Earwig, Doru lineare, as a Predator of Larvae of the Fall Armyworm, Spodoptera frugiperda: A Functional Response Study," our Lined Earwig, Doru taeniatum, is reported to feed on egg masses producing larvae that feed on and damage corn (maize) crops. This suggests that Lined Earwigs could be deployed into fields for biological control. However, appropriate field studies haven't been conducted, even as corn-eating insects become immune to insecticides.

More web pages are dedicated to how to kill earwigs than how to take advantage of their eating eggs and larvae of insects plaguing agricultural crops. In fact, the similar looking invasive Common Earwigs, which have been studied much better than our Lined Earwigs, is known to prey not only on other insects, but also strawberries, lettuce, potatoes, roses and much more.

It's one of those good/bad things, depending on one's perspective.