Longhorn beetles are a very large family of insects (Cerambycidae) with over 26,000 species! While they can vary greatly in size, color, and shape, they share some distinctive common traits: they are wood-boring insects, with extra long antennae. Unlike some other beetles, longhorns have antennae that are as long or longer than the length of their bodies! This guide will help you identify the most commonly seen longhorns of Hawai’i island.
The Queensland Longhorn beetle is a pest of numerous trees including cacao, avocado, citrus, kukui, and more. QLB is rather large, sometimes more than 1.5 inches long (not including antenna). They are solid brown with a velvety appearance. Their most telling feature is the pair of large spines on their thorax (the body segment behind the head). This picture shows that their size does vary a bit, but even the smaller ones are generally still larger than the majority of the other longhorns you might encounter in Hawaii.
The plumeria borer (also known as the plumeria stem borer), is a pest to plumeria, burrowing into the tree and damaging or killing branches. It has also been know to use cacao or kukui as a host plant (similar to QLB). This beetle is the stockiest of the longhorn beetles in this guide, although only about a half-inch long. They have a mottled brown color, and upon close inspection you can spot tiny spines on the thorax.
The lantana longhorn is a “helper” because it feeds on the lantana plant, which is toxic to people and livestock. They were released as a biocontrol to help control lantana in Hawaii’s pastures. P. spinipennis are about 1 inch long, mostly brown, and have a pair of spines on thorax. The easiest way to ID a lantana longhorn is through the four white markings on its back.
Cercium unicolor doesn’t have a common name. It’s one of the smaller longhorns, reaching only about 1/2 inch long. They are solid brown and look “fuzzy,” with no markings or spines. They bore into a variety of host plants, but are not known to be a major pest in Hawaii.
The monkeypod round headed borer is a pest to monkeypod trees. They are about 1 inch long. Their head and thorax is a dark brown and their back is a lighter shade with two symmetrical black lines. Their thorax is rounded with no spines.
The eucalyptus longhorned borer is a pest to eucalyptus trees. They are about 1 inch long with a black body and brown legs, and distinctive brown markings on their back. Unlike the other longhorns, each antenna segment has a spike on the side.
Unlike the other longhorn listed here, the koa longhorn beetle is native to Hawaii! They are slightly larger than the QLB, making them the giants of this guide. They are black or dark brown with no colored markings or spines. Their wings are leathery and veiny-looking. They are sometimes mistaken for a B-52 cockroach, especially in flight. They are most likely to be found in areas with populations of koa trees nearby.