Published in Yard & Garden Line News, September 1, 2003
People have noticed large numbers of soldiers beetles, Chauliognatha pennsylvanicus in gardens this summer. They are about ½ inch long, yellowish to tannish brown with soft wing covers. They have a black head, black legs with a black spot behind the head and an oval, black spot on each wing cover. Their wing covers do not completely cover the body, leaving a couple of abdominal segments exposed. Their head is clearly visible and like other beetles they have chewing mouthparts. Soldier beetles are related to fireflies but lack the light-producing organs that fireflies possess.
Soldier beetles overwinter as larvae. During spring they are active in leaf litter, plant debris, loose soil, and other areas where high humidity occurs. They are predaceous, feeding primarily on insect eggs and larvae. Larvae resemble miniature alligators, are usually dark colored and can grow up to 3/4 inch long. Even though the adults are very conspicuous, people would rarely, if ever, see soldier beetle larvae.
Larvae pupate apparently sometime in early summer with adults first emerging in late July. They are active through August and into September. Adults will lay eggs some time at the end of the summer which shortly hatch into larvae. They remain in this stage for the winter. There is one generation a year.
Adult soldier beetles are commonly found on plant foliage and flowers of many (many) types of herbaceous plants. Just a few examples of where they have been seen include goldenrod, helianthus, coneflower, tansy, zinnia, marigold, and globe thistle. They feed primarily on pollen and nectar. There have been reports in the literature that they are also predaceous but current researchers believe that these observations are erroneous.
Soldier beetles are very active and readily fly, often resembling wasps in flight. They can also resemble bees by moving quickly and often between flowers. Because of their frequent contact with flowers, soldier beetles are important pollinators. Flowers must bring out the romantic side of soldier beetles as they are often found mating on them.
Although they are vulnerable out in the open, soldier beetles protect themselves by secreting defensive chemical compounds to make them a less tasty treat. In fact their yellowish color is thought to be a warning signal to predators that they don't taste good, much in the same way as monarchs are colored orange to advertise their distastefulness.
Some gardeners become concerned when they see so many beetles. They figure too many of one insect can't be good. But fortunately in this case, that isn't true. They do not damage flowers or other plants and are also harmless to people, making it unnecessary to control them. In fact they are beneficial because they are predators (larvae) and pollinators (adults). Just ignore them and they will go away on their own.