The Wingless Canker Worms

What’s in a name? One answer to this well-known query may be found in the host of names given to the caterpillars or larvae of a large family of moths. There are various common, general and local names applied to these insects, among which we find "spanworms," "measuring worms," "inchworms," "measurers," "loopers" and "surveyors." Scientifically their family name is Geometridae meaning "earth measurers." Their peculiar gait having gained for them all of these names, because they seem to measure the road over which they travel, thus we find that a number of different names may mean virtually one and the same thing.

Geometrid caterpillars are so constructed that they cannot proceed after the usual fashion of such creatures. They differ from other caterpillars, most of which have five pairs of false legs or claspers, in having two pairs, which are set closely together at the very end of the body. When one of these caterpillars wishes to move, it clings very firmly with its six true legs which are on the segments close to the head; it loosens the grasp of its claspers at the hind end and draws them close to the true legs, so that the body between is arched into the form of a loop. The claspers are then fixed tightly to the object on which the caterpillar is moving, and the body is stretched out again in order to find a fresh foothold for the true legs. This mode of progression is not ungraceful, and the caterpillar forming its loops in quick succession gets along at a remarkable pace.

Many of these caterpillars spend their time stretched out at full length with the body motionless and rigid. Often at an angle to the twig or leaf on which they are clinging by the hinder two pair of claspers, they look amazingly like a short or broken twig. Their skins are never hairy but are colored brown like bark with tints of yellow, green and gray, knobbed or scarred like buds and leaf scar, and withered or furrowed just like the bark of branches and twigs. Thus we learn that Nature in dressing up some of her children in masquerade attire has a definite purpose, which in this instance is a very effective case of protective resemblance.

In this rigid, motionless attitude they so exactly resemble the twigs that not only birds and other enemies are deceived but even insect students are often misted arid take the caterpillars for twigs. This is one reason why they are not more often noticed, although they are common all over the country. Feeding upon the foliage of a great variety of plants, a few of the Geometrida are troublesome pests. Perhaps the best known of these are the "canker worms." The moths of most of the species are known by their slender bodies, small heads, and very broad wings, which are also frail and thin. The female moths of some of the species, such as the "canker worms," are wingless.

By: davidbunch

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