Cicadas and locusts are not the same insect, despite often being mistaken for one another when they appear in large numbers. They belong to entirely separate biological orders. While both insects can generate intense natural spectacles, the differences in their anatomy, life cycle, and behavior are profound. The confusion between the two is rooted in a historical misapplication of terms rather than any true biological similarity.
Distinct Biological Classifications
The difference between these two insects lies in their scientific classification, which dictates their body structure and function. Cicadas belong to the order Hemiptera, commonly known as the “true bugs,” which includes insects like aphids and leafhoppers. True bugs are defined by their specialized mouthparts, modified into a straw-like rostrum designed exclusively for sucking fluids.
Locusts, conversely, are short-horned grasshoppers and fall under the order Orthoptera, alongside crickets and katydids. Their physical structure includes powerful hind legs adapted for jumping. Locusts possess strong mandibles, or chewing mouthparts, which they use to shear and consume solid plant tissue. This difference in feeding apparatus places them in two distinct evolutionary groups.
Defining Differences in Behavior and Life Cycle
The behavioral patterns of the two insects demonstrate a clear separation in their ecological roles. Cicadas are known for their exceptionally long, subterranean life cycles, with nymphs of the periodical species spending 13 or 17 years feeding on xylem fluids from tree roots. Adult cicadas feed minimally by sipping tree sap, which generally causes little damage to mature plants.
Locusts have a short life cycle lasting only a few months and are notorious for their aggressive feeding habits. When population density is high, they undergo a complete behavioral and physical transformation called phase polymorphism, switching from a solitary phase to a gregarious swarming phase. This switch is triggered by the release of the neurotransmitter serotonin, which fuels their intense appetite and coordinated movement.
The sounds produced by the two insects rely on entirely different anatomical mechanisms. Male cicadas generate their loud, characteristic buzzing using a pair of complex, ribbed membranes on their abdomen called tymbals. The rapid flexing of these tymbals, amplified by air sacs, is a mating call known as cymbalization.
Locusts produce sound through stridulation, a process where they rub one body part, such as a leg or wing, against another to create a chirping or scraping noise. The large-scale appearance of cicadas is a synchronized emergence for mating. A true locust swarm is a highly mobile, coordinated migration of millions of insects capable of consuming vast fields of crops in a single day.
Why the Terms Are Confused
The misnaming of cicadas as “locusts” is a historical legacy stemming from the early colonial period in North America. When European settlers first encountered the massive, synchronized emergences of periodical cicadas in the 17th century, they were unfamiliar with the insect. The sheer number reminded them of the biblical plagues of locusts that destroyed crops in the Old World.
The term “locust” was thus mistakenly applied to the periodical cicada, particularly the 17-year species, and the name stuck in common vernacular. True locusts, which are swarming grasshoppers, were historically present in North America, such as the now-extinct Rocky Mountain locust, but they are generally absent today. The name “17-year locust” remains a common, though scientifically incorrect, label for the periodical cicada.