Eleodes, Pinacate Beetle, Darkling Beetle, Clown Beetle—all nicer names than Stink Bug

by Pat Flanagan

Now that the ground is a bit cooler, more and more Eleodes are seen wandering about doing their day job as one of nature’s recyclers. They dine on bits of decaying vegetation, old animal parts, and other small stuff.  If we give them any thought at all it is because of their reputation as stink bugs! When I was growing up they were so common as to be unnoticeable except when their black butts pointed skyward, a warning that they will, when threatened, release a powerful and foul oily spray guaranteed to put you (or a smaller hungry mammal or bird) off.

As an adult wandering in the desert one warm day I came across an old tire packed with about 100 mating Eleodes, oblivious to everything including the fact that they couldn’t get out of the tire, not ever. That realization brought them into focus and I have been paying attention ever since — even if it is only to greet them in passing.

These insects are remarkable for several reasons. They cannot fly, they are black yet live in some of the hottest places on earth, and they defend themselves with a stinky spray.

 Not fly! Look carefully and you will see that the upper wings, or elytra, are fused shut, unable to open. Why this should be I can only speculate. The beetle’s life cycle, including grub and adult, is connected to feeding on detritus, small broken down bits of vegetable and animal matter. Their focus is down and close to the ground. Maybe if they were flying, the desert winds would transport them to unsuitable habitat.

As for being black in the desert…this beetle and its relatives can escape the heat of the day and lower their water needs by remaining buried in the sand where temperatures are lower.  Interestingly, the black color can also help the beetle warm up on cold mornings. Later in the day, the same black color prevents the solar rays from penetrating deep into their body, helping them to stay cooler under higher temperatures. This also helps explain the color of ravens, another black desert dweller.

The black color, contrasting against the light color of the sandy desert floor, is an obvious warning to predators. Animals with obvious defenses, such as skunks, need to visibly remind predators of past unpleasant experiences so the predators won’t try again.

A successful predator of the darkling beetle is the grasshopper mouse. Using its front paws it sticks the abdomen into the ground before eating the tastier head and thorax.

As for the beetles in the tire I placed a stick from the inside of the tire to the rim and another from the rim to the ground so they could climb out after their love feast. I felt like a hero.