Lots Of Evidence Of Twig-Girdler Beetles
Ro Wauer, April 27, 2003, The Victoria Advocate, © 2003
There is lots of evidence of twig-girdling beetle activity of late. Hundreds of twigs from my cedar elm trees litter the ground. More are added to the number each windy day as the twigs break off from the larger twigs and fall to the ground. A close examination of each twig reveals a blunt end. That evidence suggests that it is the result of a twig-girdler beetle, a species of longhorn beetle of the family Cerambycidae.
Although the South Texas twig-girdler beetle is only about an inch in length with antennae about the same length as its body, it is able to cut twigs that may be almost an inch thick. Evidence of their work is fairly easy to detect; the cut twigs are all neatly severed with a blunt edge, rather than being jagged as if they were torn off by the wind or by a bird. Also, the newer twigs still support leaves, although these will wither and die soon afterward. The twigs break where they are girdled and fall to the ground. Thus the cause of the clutter we see this time of year.
Twig-girdler beetles spend considerable time as larvae within the fallen twigs. In spring, the larvae pupate within the stems, and the adults emerge a few weeks later. After mating, female twig-girdlers fly into a nearby tree, lay their eggs on the tips of the twigs, and then crawl down the twig and cut a circle around it. This action will kill the isolated twig tip, apparently a condition better suited for certain stages of the insect's development. The adults then fly off. When the eggs hatch, the resultant larvae burrow into the twig and consume the dying wood; they may remain there for a period of two to three years.
Longhorned beetles are a members of a huge group of insects with more than 24,000 species worldwide, and 1,100 in North America. They range in size from 1/8-inch to the five-inch Titanus giganteus of Brazil, a huge reddish brown creature that may be 1 1/2-inch wide. Some species possess antennae that are two to four times the length of their body. One 3-inch species that lives in New Guinea possesses antennae that may grow to seven inches in length.
All of the longhorned beetle larvae feed on wood from either live or dead trees. During the larval or grub stage they are sometimes considered delicacies by various native peoples. They are especially prized in Australia and South America. The larvae are extracted and toasted until brown and crisp, somewhat like certain cocktail snacks. Recent reality TV shows have utilized some of these creatures, both alive and dead.
Since longhorned beetles usually fly at night, they are not regularly encountered. Finding these fascinating creatures in their natural settings will require careful observations, since most are about the same coloration as the woody material that they inhabit. And to experience a tasty larva will require even more effort and considerable patience to examine a cut twig, extract one of the tiny inhabitants, and toast it to a crispy brown. It's a special treat somewhere!