Friday, July 15, 2005
Red Milkweed Beetle
When and where found: I found the one in the photo at Foss Farm on July 1
Identifying characteristics: The red milkweed beetle is red with black spots and is about half to three quarters of an inch long. Like all members of the longhorned beetle family, it has antennae which are at least half as long as its body. There are no rings on the antennae — this helps distinguish the red milkweed beetle from some other Tetraopes species. Another characteristic shared by the Cerambycidae is a region of tiny grooves called a stridulitrum. It is on the thorax and you can't see it, but if you pick up a beetle in this family it will use the stridulitrum to make a squeak or chirping sound. You don't have to squeeze the beetle — just holding it is enough to cause the sound. I found it to be a high-pitched buzz and I had to hold the beetle very close to my ear to be able to hear it.
Food: Both larvae and adults of the red milkweed beetle feed on various milkweed plants. The beetles at Foss Farm were on the common milkweed, Asclepias syriaca. Although this is the staple in the red milkweed beetle diet, the beetle does not care for the sticky milky juice that oozes from any cut surface on the plant. It prepares its veggies for dinner by first severing the central vein in the leaf, usually about a third of the way back from the leaf tip. This prevents the milky juice from reaching the tip of the leaf where the beetle goes to dine. If you look at a stand of common milkweed, you will probably find several leaves missing their tips. If you then look under the leaf, you will see the mark on the vein where it was cut.
Other milkweed insects: If you find a red and black insect on a milkweed plant, it might be the milkweed bug. You can easily tell the beetles from the bugs by looking at the way the wing covers meet. In beetles, the wing covers don't overlap but just touch each other making a straight line down the center of the abdomen. The wing covers of milkweed bugs overlap making a pattern of triangles on their abdomens. The best-known milkweed visitor is the Monarch butterfly. The caterpillar is easy to recognize by the white, black and yellow bands.
References: Richard E. White, Peterson Field Guide to Beetles; Douglas Yanega, Field Guide to Northeastern Longhorned Beetles.
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