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Mystery Insect (05/12/16)

This large worm (or larva) about 2 inches long was found tunneling into the heartwood of an old ash tree near Minot, ND.

Mystery Insect

This large worm (or larva) about 2 inches long was found tunneling into the heartwood of an old ash tree near Minot, ND. The homeowner was concerned that it was emerald ash borer; however, it is NOT an emerald ash borer larva. See NDSU Extension bulletin on E1634 Emerald ash borer. It was identified as a carpenterworm (or carpenter moth, Prionoxystus robiniae). They attack a variety of trees including ash, black locust, cottonwood, elm, oak and willow. Larvae feed on the sapwood and, as they mature, on the heartwood. Larval feeding injury creates large tunnels about ⅜–½ inch wide in the wood. Trees damaged by carpenterworms are more susceptible to limbs breaking during wind storms. They have a long life cycle of 3-4 years in ND. They attack only sick or old trees, so the best defense is keeping the tree healthy.

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Janet J. Knodel

Extension Entomologist

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