If gardeners do not pay attention, they can strip a tree before gardeners even have time to swear and spray.”Īdult cankerworms lay their eggs in late fall to early winter or early spring, he said. “I have seen them defoliate a small grove of Gambel oak in a matter of days.

“Often cankerworms can do major damage before anyone notices,” said Goodspeed. These markings act as a camouflage and make them very hard to detect, especially when they are small. Many inchworms or cankerworms are green with small dark strips running the length of their bodies, he said. The tree that gets the brunt of the attack from these caterpillars is the oak.” “I thought kids were voracious eaters, but they are mere amateurs compared to these caterpillars.

“It is amazing how much this small caterpillar can eat,” said Goodspeed. They look like they are measuring the leaf as they move along, which likely explains how they got the name inch or measuring worm. With this type of anatomy, they form a loop as they creep along leaves, said Jerry Goodspeed, Utah State University Extension horticulturist. They have legs only on the front and back of their bodies. Cankerworms and other similar insects are called inchworms because of the way they move.

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