Our Window on Nature

. . . exploring the world around us

Watching Doodlebugs

Filed under: Bugs — Lowell Christie -- May 7, 2016 @ 8:16 pm

DoodlebugIt’s often much easier to find the tracks or marks a critter leaves than to discover the track maker. But sometimes you’re just not looking closely enough. Take the case of the doodlebug.

We had seen doodlebug holes and trails long before we knew who made them. They usually occur in sandy locations, and the holes are perfectly symmetrical cone-shaped depressions an inch or two deep. They look as though someone had poked a stick into the sand while strolling by. Often you will see multiple holes in an appropriate area. And hidden at the bottom of the hole is the doodlebug.

Doodlebug is just one of the nicknames for the creature that digs these holes. They are made by the larval stage of the family of insects called Myrmeleontidae, better known as antlions. It’s hard to tell whether the name antlion or doodlebug is more difficult to explain.

Antlion probably comes from their ferocity in eating ants and other small insects. And some think that doodlebug comes from the twists and turns of the trail they leave while looking for a suitable digging spot. It does somewhat resemble the aimless “doodling” you might create with pen or pencil when your mind is wandering. But there’s no question that either name is easier to say than Myrmeleon.

We first discovered antlions while living in our motorhome outside of Tucson, Arizona. Kaye had heard about them while working as a volunteer interpreter at the Arizona Sonora Desert Museum, and since we had sandy areas just a short walk from our site we decided to capture a few and study how they lived.

The capture itself was fairly simple.  After using a small trowel to transfer sand containing antlions into a cardboard box, we soon had a study plot sitting on the corner of our desk. Big mistake. The first thing we learned was that antlions, while digging their pits, throw sand out of the depression. And they throw it farther than we expected. We had sand on the desk, sand in the carpet, and before we got sand in the computer keyboard we decided to study the critters in their home environment.

A doodlebug creates its pit by moving backwards in an ever-decreasing circle. After defining the outside diameter of the pit, it uses its body as a bulldozer, gradually moving towards the center of the hole as it digs deeper. Using one leg to place loose sand upon its head, a sudden twitch throws the material out of the way.

When it finally reaches the center and bottom of the hole, the antlion buries itself in the pit and waits for dinner.  Because, you see, an antlion pit is a very well-designed trap. The sloped edges of the pit match the property of granular materials that engineers call the angle of repose.

If you have some sand (or salt or sugar) available, try this experiment. Pour the material into a small, tall pile. You’ll find that there is a physical limit to how steep the sloping edge can be. This is the angle of repose for that particular material. Any additional material added will cause a landslide.

The doodlebug creates this same slope for the edges of its pit, and any wandering insect venturing onto the slope ends up in the lion’s mouth. Just to make sure, when the antlion notices a visitor, it may toss additional grains of sand to encourage the preys decent. Whether the barrage actually hits its target is of little importance, since removing more material from the bottom of the pit undermines the sides, increasing the likelihood of an edible landslide.

Eventually, of course, the doodlebug grows up. Few people see the adult form of the antlion since it is only active in the evening. Although it resembles an adult damsel- or dragonfly, antlions belong to an entirely different insect order. They have worldwide distribution, and some live under dead leaves or wood instead of digging pits.  However the pit-digging doodlebug is certainly easier to find and much more fun to watch.

People studying antlions have discovered some fascinating facts. The pit itself can be dug in as little as fifteen minutes. Surprisingly, the size of the pit is not necessarily related to the size of the creature digging it. It turns out that the longer the antlion goes without food, the larger the pit it digs. There is also an odd relationship between the size of the hole and lunar phases; the hole is larger when built during the full moon.

With the antlion being so widespread, it’s not surprising that mention of it turns up in the literature of many countries. Mark Twain (Samuel Clemens) played with the folklore of the doodlebug as fortune teller when he had Tom Sawyer talking into a sandy hole in the ground saying:

“Doodlebug, doodlebug, tell me what I want to know! Doodlebug, doodlebug, tell me what I want to know!” The sand began to work, and presently a small black bug appeared for a second and then darted under again in a fright.

And that’s about what happens when you try to see the doodlebug in his den. They do their best to stay buried at the bottom, but if you look carefully you can sometimes see their oversized mandibles protruding from the sand as they wait for their prey.

We discovered a method for “extracting” a doodlebug from his burrow in a most unexpected source. In the transcripts from the Apollo 16 expedition to the moon, lunar module pilot Charles Duke was trying to describe one of the lunar craters to those back in Mission Control. He compared it to a doodlebug hole, but then had to explain what a doodlebug was to the mystified listeners.

Yeah, they burrowed in sand. And we used to have a rhyme. I can’t remember. You take a little piece straw off a broom and ‘Doodlebug, doodlebug, are you at home?’ And you’d spin this little piece of straw around in this little doodlebug hole and, if he was there, eventually you’d work him up to the top.”

We’re planning to try that the next time we go doodlebug watching.

FMCA0607

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