Reconnect With Nature Blog

Tenebrionid Headstands

Doug Von Gausig has very kindly provided two pictures of tenebrionid beetles doing headstands. Both are species of Eleodes. One species has grooves along the elytra (the fused front wings of the beetle -- remember, these are flightless beetles that walk around on the ground), and the other one has smooth elytra. Each species has defensive secretions. The grooves probably help the defensive secretions spread out across the elytra, coating them with quinones and hydrocarbons that repel predators. Interestingly, some tenebrionids have receptors that are sensitive to the breath of mammals. When these receptors register the heat, moisture, and odors of mammalian breath, the glands evert, spilling out their noxious substances.  Here's a challenge for some of you beetle fans: Can you identify these two species of Eleodes?

   

Beetle Defensive Secretions

Chris Wemmer, a distinguished mammalogist and conservation biologist, suggests that it might be interesting to taste an Eleodes beetle (see comment). I don’t think that this would be a good experience. Some years ago, I was doing a study of biodiversity on one of the islands in the Gulf of California. As part of the study, I was trying to count the number and species of Tenebrionid beetles on the island. Because desert animals switch to being nocturnal during the heat of the summer, the beetles were active only at night. I set up a 200 meter transect, and walked along this transect every 30 minutes, counting the number of beetles that I saw and identifying each species. Since it was quite dark at night, I set up the transect between two large Cardon cacti (Pachycereus pringlei) that served as landmarks for me to steer by.

Around midnight I stopped to pick up an Eleodes beetle that I could not identify to species. I inspected the beetle in my flashlight beam, then set it down and watched it scuttle away. During the time I was holding it, the beetle must have sprayed my fingers. I could smell the pungent, almost sweet smell of defensive secretions, but I thought that the beetle had gotten the secretions on its own body, and not on me.

It was a hot July night, and sweat was pouring down my face. Without thinking, I brushed my fingers across my moustache, wiping off the sweat. Suddenly it felt like a sledge hammer hit my sinuses. It was like eating a huge dollop of Japanese wasabi (Eutrema wasabi), the green horse radish-like herb that comes with sushi, but much worse. My eyes started tearing, and liquid was flowing copiously out of my nostrils. I could barely breathe.

After a few minutes, my sinuses settled down, but the worst was still to come. As I tried to walk the transect, I found that I could not steer in a straight line. I could see the Cardon at one end of the transect, and I tried to walk toward it, but I kept drifting off to either the right or the left from the straight line, without being able to control where I was walking. I tried for about half an hour, and finally gave up, sitting down in the dirt with my head in my hands.  Two hours later the effect seemed to go away, and I was able to get back to my camp and roll into my sleeping bag. The next morning I was fine.

Having smelled the defensive secretions of a number of different species of Tenebrionids, I can say that not all secretions have that effect. Some merely cause a watering of the eyes and a tanning response in which the skin that has been sprayed turns brown.  But some defensive secretions are apparently quite potent. I try to imagine what it would have been like to taste the secretions of that beetle. Somehow, my imagination fails me.

Watching Snake Behavior

Doug Von Gausig (see previous post and comment), who is an accomplished photographer and nature recordist, sent me a video of a patch-nosed snake (Salvadora hexalepsis) excavating a burrow (watch the video).  In this video, you can see some fascinating behavior.  The snake goes into the burrow, apparently loops its body around some sandy soil, emerges holding on to the soil with a coil of its body, and releases the soil away from the burrow.  This is an elegant solution to excavation. I have often wondered how snakes manage to dig burrows without having hands. Now I know.

As I was watching the video, I was reminded of watching Sphecid wasps (genus Ammophila) excavating burrows. A wasp would go into the burrow, apparently use its legs to scrape up some dirt, put the dirt between the coxae of her hind legs, back out of the burrow, fly up into the air for about one meter, and release the dirt, which blew away in the wind as a fine plume. The wasp would do this over and over, making sure that no dirt was piled up at the entrance to the burrow as a tell-tale sign of activity for predators and parasites to notice.

I tried to photograph this activity. I found a wasp that was just starting to dig her nest and set up my camera. After a few of her forays in dropping the dirt, I realized that I had a better camera angle if I moved around to the other side of the burrow. I set up the camera again and waited for the wasp to emerge. She did, and instead of flying back, she flew around on the other side of me and started searching for her burrow. At first I was puzzled, but then I remembered the classic Tinbergen experiments with wasps and pine cones. She was using me as a landmark to find her burrow, and did not realize that the landmark had moved. So she was completely disoriented. Needless to say, I moved back to my original position, and she promptly found her burrow.

But back to the patch-nosed snake. I found it very interested that after emerging, the snake spent some time looking around, apparently watching for potential predators. Digging burrows must be a dangerous activity for snakes. A predatory bird or mammal could sneak up on the snake when its head was inside the burrow and grab it before it had a chance to react.

Watching animals like this is an excellent way of reconnecting with nature. Not only do you get a sense of what their behavior is like, but you also can get a sense of what might be important in their lives. And then you can ask yourself the question, are similar problems important to your life?

Mimicry in Beetles

Doug Von Gausig (see comment) asks an interesting question about Tenebrionids. He asks whether there are any Carabid beetles that do a head-stand display like the Tenebrionids, or if it is only the Tenebrionds that do this.

The situation among these beetles is complex. There are a number of Tenebrionid beetles (many in the genus Eleodes) that do the headstand display and have defensive sections. Many of these species look very similar to one another, in an apparent display of Mullerian mimicry, where all of the species converge on a similar phenotype so that predators can learn a general color and body type and know that everything that looks like that is either toxic or distasteful. Some of these beetles have smooth elytra (the wing coverings, which in the case of these beetles are fused together because the beetles are incapable of flying), while others have grooves on the elytra.

These beetles need an ample supply of moisture (that they get from eating moist vegetation or drinking dew) to manufacture the defensive secretions. When they do not get the moisture that they need, they do not do the headstand display, but attempt to run away from a potential predator.

There are other Tenebrionid beetles that will also do a headstand display, but lack any capability of producing defensive sections. These are beetles in such genera as Gonasida and Stenomorpha. They look just like the beetles with defensive secretions, have the same behavior, and are found in the same places. As such, they are Batesian mimics. Batesian mimicry is where there is a model that is dangerous or distasteful, and a mimic that is edible but looks and acts like the model.  Some of these species have grooved elytra while others have smooth ones, just like the species of beetle with defensive sections that they are mimicking.

Then there are Cerambycid beetles, or long-horn beetles, in the genus Moneilema that mimic the Tenebrionid beetles with defensive secretions.  These beetles are shiny-black, with smooth elytra, and do a headstand just like the Eleodes, but lack any defensive secretions. Unlike many long-horn beetles (who are called that because most members of that family have long antennae), these beetles have short antennae. However, their antennae are still longer than the Tenebrionids, who have really short filamentous antennae. So the Moneliema have an interesting adaptation. They have a groove running along the length of their body into which they can insert their longer antennae, making the antennae seem to disappear. One potential hitch about doing this is that there is a gray area along their body where the thorax is connected to the abdomen, and a black antenna would be visible against this gray background. To counteract this, the Moneilema have a gray segment in an otherwise black antenna, and this gray segment exactly matches the color and position of the gray area between the thorax and the abdomen. When the Moneilema do their headstand, they look just like the Tenebrionids with defensive secretions.

Finally, there are the Carabid beetles. Some of these beetles are also black, and are roughly the same size and shape as the Eleodes. For example, the beetle Scaphinotus petersi looks superficially like some of the Eleodes, but runs quite fast and low along the ground, instead of walking relatively slowly like the large Tenebrionids described above. I am not aware of any of the Carabid beetles doing a headstand display. although many Carabids have defensive secretions. They seem to rely on speed to get away from their predators. Some Carabids such as the bombardier beetles (Brachinus) have defensive secretions that mix in an internal chamber and literally explode out of the rear of the beetles in a hot burst (100 degrees Centigrade) of fluids.

An interesting question is how this mimicry might have evolved.  For a predator to learn that a beetle is distasteful, the predator has to first taste the beetle, something that often proves to be fatal to the beetle. We have to assume that a small mutation that makes a non-toxic beetle look slightly more like a toxic one is enough to lower predation pressure on that beetle, and over millions of years the mutations that result in closer convergence are those that survive in the gene pool through natural selection. Personally, I have to marvel at how good that convergence can be in this beetle mimicry system and in other insects with Batesian and Mullerian mimicry.

Watching Beetles

I was walking my dog around our local pond when I noticed two people, a man and a woman, peering down at something on the path. I stopped well behind them to give them space. At the same time, I tried to see what it was that they were observing. At first, I could not see anything. Then, suddenly, I noticed a black dot moving on the path. Now I knew what had captivated their attention.

They were looking at a Tenebrionid darkling beetle (Eleodes longicollis, family Tenebrionidae). This beetle is black, completely flightless, and about 26 mm long (a little longer than one inch).  As they would get close to the beetle, it would do a headstand, lifting its butt up into the air and standing very still. After a while, sensing no movement, the beetle would lower its butt down and start to move along the path, Fascinated, the people would move closer, casting their shadows on the beetle, which would stop and raise its butt up again. Clearly, the people were engrossed in watching this behavior.

I thought of coming up to them and telling them a few facts about these beetles.

I wanted to tell them that these beetles have defensive secretions, made up of quinones and hydrocarbons, that they squirt out of glands near their anus at predators who try to eat them. This is a great defense against predatory birds and small mammals. However, it doesn’t work against the carnivorous Grasshopper Mouse (Onychomys leucogaster). Experienced mice come up to a beetle that is doing a headstand defensive display, grab the beetle with their front paws, turn the beetle around, and stick the beetle’s butt into the sand. With the beetle’s defenses immobilized, the mouse chews off the beetle’s head, and then proceeds to eat at leisure down to the level of the defensive glands. Some mice go on killing sprees. Sometimes you can find a row of 10 or more beetles stuck with their butts into the sand, positioned like telephone poles, all with their heads chewed off but otherwise uneaten.

The defense doesn’t work against Striped Skunks (Mephitis mephitis) either. When a skunk comes across a beetle doing its headstand display, the skunk first sniffs the butt end of the beetle. If the skunk detects the odor of defensive secretions, he then starts to roll the beetle around in the sand with his front paws. Meanwhile, the beetle is releasing its defensive secretions. Periodically, the skunk will stop the rolling and take a small taste of the beetle. If there are still defensive secretions present, the skunk will shake his head vigorously several times and then continue rolling. Once the beetle has exhausted its supply of secretions, the skunk proceeds to eat it.

However, the beetle’s secretions work well against Harvester Ants (Pogonomyrmex rugosus). The ants have a disk-shaped area around their nest opening, onto which foraging workers drop seeds and bits of vegetation that they pick up anywhere within about 100 meters (300 feet) of the colony. Other workers emerge from the nest, pick up these seeds and droppings, and take them down inside.  The Tenebrionid beetles come into these disk-shaped areas and feed on the seeds and vegetation that the ants have brought. If the ants try to sting or otherwise attack them, the beetles spray minute quantities of defensive secretions, with great accuracy, at the approaching ants, causing them to immediately stop, curl up into a C-shape, and start cleaning themselves. On days when the ants are particularly aggressive, you can see a beetle leisurely feeding while perhaps 10 or more ants are frantically cleaning themselves nearby.

I wanted to tell these people all of that. But I didn’t. Instead, I waited until the beetle left the path completely and was lost in the surrounding vegetation, and then I walked past them, merely saying Hello.

Sometimes, there is a place for lots of information. Other times, there is a place for simply watching and appreciating what nature has to offer.