Robin’s carpenterworm (Prionoxystus robiniae), A Very Large Micromoth

Robin’s carpenterworm

Photo by Bill Reynolds

Micromoth is an artificial grouping having no taxonomic equivalent. The name suggests that these are small moths, and indeed most have a wingspans of less than ¾″. However, micromoths are not distinguished by size but by wing venation and the female reproductive tract.

Carpenterworms are wood-boring micromoths. The caterpillars feed by boring into the cambium layer of a tree. This creates galleries and tunnels under the outer bark that decrease the value of the wood and can sometimes kill the tree. Wood has little nutritional value. As a result, the caterpillars take 3 or 4 years to complete their life cycle. They pupate in the spring of their final year and emerge as adults between May and July.

Robin’s carpenterworm (Prionoxystus robiniae) is a medium-sized moth but a very large micromoth. Adults are 11 ⁄16″ to 1¾″ long with a wingspan of 17 ⁄16″ to 3⅜″. They are similar in size and appearance to sphinx moths and are often misidentified as such. They are distinguished by their large size, heavy body, abdomen that extends well beyond the hind wings, light gray wings with a net-like overlay of thin dark lines, accessory cell and 2 complete anal veins on the forewing, 3 anal veins on the hindwing, and yellowish-orange patch on the hindwing of the male.

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