Cottonwood Borer

The cottonwood borer is a large and visually striking member of the longhorn beetle family (Cerambycidae), named for its close association with cottonwood, poplar, and willow trees, in whose roots and lower trunk its larvae develop. Its size and dramatic black-and-white pattern make it one of the more recognizable longhorn beetles in North America.

Adults are most often encountered resting on the bark of host trees during the summer months, where their bold coloring provides some camouflage against dappled light and shadow on tree trunks. The species belongs to the subfamily Lamiinae, the flat-faced longhorns, a group characterized by a downward-angled head and often elaborate antennal length.

As a wood- and root-boring insect, the cottonwood borer contributes to the natural process of tree decline and decomposition, particularly in stressed or mature trees, and is part of the broader community of insects associated with riparian cottonwood forests.

• Adult: 25–38 mm, a large, robust longhorn beetle with a strongly mottled black-and-chalky-white checkerboard pattern across the elytra and pronotum.
• Antennae are long, banded black and white, and typically as long as or longer than the body.
• Legs are thick and marked with the same black-and-white pattern as the body.
• Lookalikes: its unique bold checkerboard coloring, large size, and consistent presence on cottonwood or poplar bark distinguish it from other longhorn beetles, which tend to be more uniformly colored or striped.

Found across much of the central and southern United States, particularly in riparian zones, floodplains, and windbreaks where cottonwood, poplar, and willow trees grow. Adults are active during the warmer months, typically mid to late summer, and are usually seen resting or walking on the lower trunk and exposed roots of host trees.

Larvae tunnel into the roots and lower trunk of cottonwood and related trees, feeding on the wood tissue as they develop, which can weaken heavily infested trees over time. Adults feed lightly on twig bark and petioles but spend much of their time resting on tree trunks or seeking mates. As root and wood borers, they are part of the natural insect community that contributes to the decline and eventual decomposition of aging or stressed cottonwoods.

Females chew small pits into the bark near the base of the tree or exposed roots and lay eggs individually within them. Larvae hatch and bore into the root and lower trunk tissue, feeding and developing over one to two years depending on climate. Mature larvae pupate within the wood, and adults chew their way out and emerge during summer. The species generally completes one generation every one to two years.