Commentary

Bob Wilson: Nothing little about inchworm’s appetite

July 11, 2014 

Citizens, the enemy is at the gates. And maybe in your house before long.

An army of inchworms, having taken Charlotte, is moving on Durham, hungrily eyeing the city’s thousands of aging willow oak trees. Those leafy oaks are in for the fight of their lives.

Many of the trees were planted in Durham and at Duke University in the 1930s.

As staff writer Jim Wise found, these senior citizens are already under stress in their urban environment. Many may fall – literally – to the inchworm invasion.

The call has gone out from a Duke-Durham initiative for volunteers to mount a defense with sticky bands placed around the tree trunks. The last resort and the one nobody wants: pesticides.

All this to combat a misnamed caterpillar that is, yes, about an inch long. Everybody has seen these little green guys arching along or hanging from a silk thread.

In small numbers, they’re not a threat. But when they show up by the millions, we got trouble in the Bull City.

So, exactly what is an inchworm, also called a cankerworm?

It’s the larval stage of the geometer moth. The wingless female lays her eggs on the underside of leaves. When the eggs hatch, the voracious, newly minted inchworms find a bounty awaiting them.

Children through the ages have been fascinated by the inchworm, an oddity in the caterpillar world because it has no feet along its middle, only at the front and back.

The inchworm appears benign in children’s stories and in a song written about them by lyricist Frank Loesser:

Inchworm, inchworm,

measuring the marigolds,

you and your arithmetic,

you’ll probably go far.

Inchworm, inchworm,

measuring the marigolds,

seems to me you’d stop and see

how beautiful they are.

Sort of hits you in the heart, no? But the pragmatic inchworm sees the marigolds not as splendor but as a buffet.

However, befitting its name, the lowly inchworm has inspired mathematical wonderment. Consider this problem from “Math Fun Facts:

You have a rubber band one meter long. An inchworm starts at one end and moves at one centimeter per second. The band stretches another meter each second (the inchworm moves with it). So does the inchworm ever reach the other end?

I won’t go into the math, but yes it does. Unfortunately, it takes so long that the universe would go dark before the inchworm crosses the finish line.

A bit faster is an exercise routine that emulates the inchworm. Of course, it’s called the inchworm exercise:

Kneel on a mat and balance yourself with your hands at the width of your shoulders. Do the same with your feet.

Head down, butt high, walk forward. Repeat exercise. (This is not one to videotape, lest it show up on “America’s Funniest Videos.”)

As you can see, the life of an inchworm isn’t one to envy in an animal world that values speed as a defense against predators. The inchworm isn’t defenseless – it can simulate a twig and rappel with a silk thread – but it is usually easy game for birds, wasps and other predators.

This year’s invasion of inchworms is well beyond the ordinary. For one thing, the usual natural controls are out of synch. Spring is coming earlier, which means inchworms appear before the migrating songbirds that feed on them.

Hence the coordinated tree-banding initiative planned for September. Some neighborhoods in Durham began banding last year, and their effort became the seed for the larger, city-wide program.

Everything rests on interrupting the geometer moth’s reproductive cycle by stopping the females from reaching the leaves and subsequent defoliation of a tree by inchworm larvae. The sticky band defense may seem a bit primitive, but it’s inexpensive and it works.

Which brings us back to the misbegotten romance of the inchworm. The Seattle Nature Preschool, an online site, tells kids that inchworms love to eat oak tree leaves.

“Maybe we can find some inchworms by finding an oak tree and looking at its leaves!”

Oh, yeah, we can help you with that one.

Bob Wilson lives in southwest Durham.

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