Naturespeak A naturalist's view of the world

July 10, 2009

Within An Inch of Life

Filed under: Uncategorized — wykes @ 9:03 pm

The odd measured gate of the geometer caterpillar is performed as if  it were laying out a property line. Whether down the length of your finger or  across the green surface of a leaf, the “earth measurer”  appears to pace out its route with careful precision. First, the body extends out to full length, tiny forelegs grab the surface, and then the back end is slowly brought forward to catch up with the head end – resulting in a highly arched mid body. Each “step” is equal and geometrically precise. There are actually over a thousand different kinds of these creatures in North America, but they all mark distance the same way. These larval members of Geometer family are better known as loopers and spanworms, but their whole public persona is based on the well-known title of inchworm. Everyone knows an inchworm when they see it…or hear about it.

Frank Loesser, the popular composer of such wartime ditties as “Heart & Soul,” “Praise the Lord and Pass the Ammunition,” and “I Don’t Want to Walk Without You” penned “The Inchworm” in 1951. You know it.  “Inchworm, inchworm measuring your marigolds” and ” Two and two is four, four and four is eight…etc.” has become part of our culture nearly as familiar as the “Itsy bitsy Spider.”  Until someone writes a song about the plain looking adult moths, the child star status rendered upon the larvae will have to do.

The inchworm look is distinctive owing to the lack of legs in the middle part of their body. Most caterpillars have 16 legs – a set of six just behind the head, a set of eight at mid body, and two more to finish off the hind end. When operating on all 16 cylinders, the average caterpillar chugs along at an even linear rate. Inchworms typically have only ten legs -the requisite six prolegs behind the head and a cluster of four at their bum end.  They are forced by this stick figure anatomy to walk the way they do.

One of the advantages of being twig-like is that they are very good at, well, looking twig-like. When danger threatens, they can “go twig” and straighten out. Smooth green inchers end up looking like broken leaf stems and the brown ones become perfect imitations of dead sticks. Some even embellish their camouflage with warty bumps and lichen like clusters. Not everyone, or everything,  is fooled by this act, however.

I stumbled across a large inchworm (more like an inch-and-a-quarter worm) in the middle of a sandy two tract road the other day. Instead of blending in, the neon green larvae stood out like a sore thumb. It was apparent that the creature was paralyzed and within an inch of his life, but not apparent who was responsible for rendering it so. After a few minutes a medium sized black wasp with a dramatic red waist band returned to the scene of the crime and answered the question (see below and here). It was a Sand or Thread-waisted wasp (Ammophila sp.). These burrowing wasps paralyze moth larvae as food for their young. They stuff them down a burrow, lay a single egg upon them, and then stop up the tunnel. When the junior wasp hatches they feast upon the flesh of their not-quite-dead burrow mate.

This wasp was exceedingly nervous about my presence and paced around the limp prey as if walking on a hot griddle. The burrow entrance was located only a few centimeters away from the head end of the larvae. It gave a half-hearted effort to drag the inchworm to the entrance, but it soon took off . I waited with the helpless little “worm” for a few minutes and attempted to explain what will happen next (see here). I ventured that he probably wouldn’t  feel a thing, although I certainly couldn’t say that with any real authority. Quoting Mr. Loesser’s song, the best I could manage as a eulogy was to say that “You and your arithmetic, you’ll probably go far.” 

There are a lot more inchworms in the world than there are sand wasps, so they’ve definitely got the advantage of numbers.

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