Special to the Reading Eagle: Mike Slater
A pair of milkweed beetles. Their antennae are sensory organs used to smell and taste.
The article last week in Berks Country about the big racks of antlers on the white-tailed deer at Kermit Fidler's farm got me thinking. I was reminded of the long "horns" some insects, such as beetles, carry around.
Proportionately, they are much bigger than the racks of those impressive bucks. Staghorn beetles and rhinoceros beetles have horns that may be one-third their body length or longer. Their "horns" are long, pointy projections of their exoskeletons from their head or sometimes their first thoracic segment. (Their wings are attached to the second and third thoracic segments.) In these large beetles, only the males have these horns and they use them when they fight for dominance just as big-horned mammals do. For the beetles, though, these duels are more like shoving or wrestling matches than head banging.
The long-horned beetles in the family Cerambycidae don't have horns but rather long antennae. The larger species in this family may have horns several inches long, from their heads to the tip of their abdomens, and have antennae that are more than twice as long as that. Many other species in this family have shorter, but still respectably long, antennae, such as the red milkweed beetle (Tetraopes tetrophthalmus). In these beetles, the eyes are relatively small and actually wrap around the base of the large antennae.
These antennae are pretty amazing-looking, but they aren't used for jousting to impress females. They are sensory organs that the insects use to smell and taste. One important use is for males to detect and locate receptive females of their own species from a distance. In some moths, the antennae serves as ears that can detect the frequencies bats use for echolocation of their prey, which include moths.
The large long-horned beetle is a white-spotted sawyer, or pine sawyer, that I photographed on a railing outside the Hawk Mountain visitor center. It is probably a male, as females have more white markings. I got help from my friends Karl Gardner and Ryan Woolwine to identify this picture and Karl tells me the larvae of this beetle eat the wood of dead or dying pines and other conifers. Their favorite trees in Pennsylvania are white pines and, farther north, balsam fir is another favorite. They apparently don't like healthy trees, possibly because healthy conifers leak sticky sap that hardens into resin when holes appear in their bark. Dying trees don't give off much of this gluey defensive liquid.
According to the U.S. Department of Agriculture, they aren't damaging to living trees very often, but can cause significant damage to pine logs after they are cut and waiting to be turned into pulp or boards. Sometimes lumbermen use insecticides to prevent this damage from the large larvae boring into the wood, but there is an organic way to reduce or prevent this damage. Keep cut pine logs in shade until they are ready to be used. Female beetles prefer to sit in the sun when they lay their eggs.
Also, these big beetle larvae will cannibalize their siblings and cousins if their burrows through the wood happen to intersect.
The red beetles pictured are more common around here. You'll find them on almost any common milkweed plant (Asclepias syriacus) in the summertime. Like monarch butterflies, these insects aren't affected by the cardiac glycoside toxins in the milkweeds. In fact, they keep them in their bodies as a defense against predators, while they advertise themselves as poisonous with their bright red color, which stands out against the green leaves. The larvae of the beetles feed underground on the roots of milkweeds.
Many smaller and less conspicuous long-horned beetles live around here. Many of them feed on flower pollen and act as pollinators of elderberries, spireas and other shrubs and herbaceous plants that bear their flowers in broad, flat clusters.
For help identifying long-horned beetles in the family Carambycidae, I recommend the "Field Guide to Northeastern Long-horned Beetles" by Douglas Yanega, 1996, published by the Illinois Natural History Survey. The survey covers 342 of the 344 species known east of the Mississippi River. Many pictures are online at www.bugguide.net (search for Cerambycidae), but there are so many that finding a match by chance can be difficult.
Mike Slater is a naturalist who lives in Brecknock Township, where he is an active member of the Mengel Natural History Society of Berks County and the Muhlenberg Botanic Society of Lancaster. He is also a member of the Baird Ornithological Club. Reach him at firstname.lastname@example.org.