Soldier beetles are beneficial insects that are common in many North American gardens and are often mistaken for an unwanted pest. Chauliognathus pensylvanicus are peaceful insects that feed on flower pollen and the occasional aphid, so are more than welcome residents in your perennial border. The species name pensylvanicus is not a mis-spelling. At the time of its naming Pensylvania was an accepted spelling (1774) and as long as it wasn't the result of a typographical error, the spelling is accepted. However, in modern times, pennsylvanicus is also commonly used.
These beetles are also known as Leatherwings, because their elytra are semi-flexible, unlike most beetles that have elytra that are hard and shell-like. Elytra are the pair of rigid wings that cover the actual flying wings of members of the Coleoptera family. The name ‘soldier beetle' was adopted because several members of the genus Chauliognathus have red and black coloration, similar to many military uniforms of the 17th and 18th Centuries.
Chauliognathus pensylvanicus and their cousins of the same genera are often mistaken for fireflies, which are close relatives. All of these beetles are peaceful and do not sting or bite humans. They feed on flower pollen and Chauliognathus pensylvanicus prefers the pollen of Solidago species (goldenrod) and it is actually nicknamed the Goldenrod Soldier Beetle. The image at left also proves that they have a taste for my giant cockscomb pollen. (Celosia argentea var. cristata)
These are day-flying beetles that prefer sunny areas and can be found in great numbers enjoying the pollen of many different plants. Since they do appear in groups, many gardeners naturally assume that they are unwelcome invaders and run for the pesticide. However, they are totally harmless to your garden and yourself. When disturbed, they may secrete droplets of a milky liquid, which in fact is a defensive mechanism. Birds, rodents, other predatory insects and spiders all seem to avoid these beetles and it is probably because of this secretion which tests confirm contain dihydromatricaria acid, an acetylenic compound. This makes them highly un palatable.
The larvae are also good guys. They can be found in leaf litter and soil, where they overwinter in rotten trees, loose bark and forest floors. They feed on caterpillars, soft-bodied insects, grubs, corn earworms, other larvae and grasshopper eggs, making them pint-sized heroes in my book. The larvae will pupate and emerge from late spring through late summer, depending on the species, but the Chauliognathus pensylvanicus is usually most numerous in late summer because they enjoy the goldenrod. Its close cousin the Margined Leatherwing, (shown at right) Chauliognathus marginatus, appears so similar that many mistake them for the same insect, but the Margined Leatherwing flies in late spring and early summer. It can be distinguished from the Goldenrod Leatherwing because the black area on its head and pronotum is a continuous band, instead of the single spot on its goldenrod-loving cousin.
Both of these beetles are beneficial predators and excellent pollinators. They are peaceful and harmless visitors in your garden, so welcome them whenever you see them.