MAY
2008

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

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Check out these books by Tom Turpin:

Flies in the face of fashion

What's Buggin You Now?

 

 

 

05-22-08

Download the audio of On Six Legs: MP3, WMV.

Insects Do Strange Things for Good Reasons


Insects, it seems, do some strange things. At least from the human perspective some insect behaviors appear a bit odd. Chances are that any insect behavior, no matter how strange it seems to humans, is somehow related to survival of the species.

Why do ants march in a line? Most of us have at one time or another noticed ants traveling along the same path. The route the ants follow may not be a straight line, and most of the time ants are traveling in both directions. Such behavior is the result of ants marking trails with formic acid. Generally this happens when scout ants leave the nest in search of food. Ants on a food-finding mission mark the route as they go, so that they can find their way back to the nest.

So when ants discover food, such as at your picnic table, the ant grabs the food and carries it back to the nest by following the chemical odor on the trail. Other foraging ants follow the same trail and soon there is a parade of workers going back and forth to the food source with each ant remarking the path with dabs of formic acid.

Why do insects fly to lights? It has long been recognized that some insects are attracted to lights. That is why collectors, pest managers and homeowners can use lights to lure insects to traps. But scientists have yet to explain the biological reason for such behavior. But there are hypotheses.

One is that insects use light from the moon and stars to navigate when they fly at night.

Relative to a little flying insect such light sources remain stationary, at least over a short period of time. So if an artificial light such as a fire or electric light bulb shows up in view, the insect's navigation system gets fouled up. The insect tries to maintain a constant angle of flight relative to the earthbound light as it passes by and ends up flying into the light.

Another hypothesis is that night-flying insects orient toward holes in the landscape, such as the space between two trees based on concentration of ultraviolet light. An artificial light appears to be an environmental open space to a flying insect, according to this line of thought. The duped insect loses its orientation and mills around in the vicinity of the light. Some people call moths "millers" because these insects "mill around the light" like a grain miller going in circles to grind grain on a millstone.

The cockroach poet archy in his poem, "the lesson of the moth," asks a moth that is flying around a light "why do you fellows pull this stunt?" The cockroach didn't get an answer but ended up admiring the moth anyway, because, "I wish there was something I wanted as badly as he wanted to fry himself."

Why do processionary caterpillars follow each other in a line? These old-world caterpillars become moths as adult insects, but, as caterpillars, they earn their name by crawling head to tail over bare ground in lines of up to 300 individuals. Apparently this procession of caterpillars is searching for soft soil in which to form their cocoons.

Why the caterpillars move head to tail while touching each other is not understood, but the behavior has been described in writing since at least 1736. Even French entomologist Fabre wrote about these insects in his essay, "The Life of the Caterpillar." This we do know: The caterpillars have stinging hairs, as anyone who has touched them can attest. So maybe this behavior helps call attention to the fact that they are dangerous to touch.

To humans, ants following trails, moths flying to lights and caterpillars crawling head to tail across the ground might seem like strange behavior. To the insects, it is all about survival!

 

 

Writer: Tom Turpin
Editor: Olivia Maddox