Jeffrey Hahn, Extension Entomologist
There are two basic types of cicadas, dog day (also called annual) and periodical cicadas. Dog day cicadas, Tibicen spp., do not have a synchronized life cycle so there are some that emerge every year in Minnesota. Periodical cicadas which do not occur in Minnesota spend 13 or 17 years as a nymph in the ground and then emerge together in tremendously large numbers.
While cicadas are present here from July into September, they are more often heard than seen. They produce a high-pitched sound during the day that resembles a powerline hum. Only the males produce this sound in order to attract females. They produce this hum by vibrating a membrane in an internal air chamber.
More commonly, people see the immature nymphs. They are dark brown and similar in appearance to the adults except that they lack wings. Some people think they look like beetles (perhaps because of their stout shape and that they lack wings) The nymphs are subterranean during their lives spending four to eight year underground feeding on tree roots.
Once they emerge from the ground, they climb up objects such as trees, posts, fences, and even the sides of buildings to finish their development. When cicada nymphs molt into adults, they leave behind 'cast skins'. Sometimes it is not until these empty shells are closely examined that some people realize that these are no live insects.
Fortunately, cicadas are not harmful or dangerous to people, pets, or property in any stage. While they do feed on trees, they do not cause any noticeable injury. If you see cicadas, just ignore them and they will eventually go away on their own. No control is necessary.