Cicadas and Locusts are often confused or considered the same thing, but they are very different. This confusion – usually seen with the identification of periodical cicadas as locusts, has been traced back to early North American colonists as researched by the College of Agricultural Science at Pennsylvania State University. With their ingrained religious teachings, they were familiar with the concept of plagues of locusts from Biblical accounts. When the swarms of periodic cicadas appeared, they assumed that these insects, indigenous to North America and therefore unfamiliar to them, were locusts.
All cicadas are members of the Homoptera order. Cicadas are related to crickets, but while crickets eat plants, cicadas have mouths which are designed to extract the juices from plants. The two types of cicadas are annual and periodical. Annual cicadas appear every Summer. Periodical cicadas appear every 13 or 17 years in large numbers. The body of the cicada is hardy and they have large eyes and broad heads. The wings of a cicada have a clear membrane that runs through them.
Periodical cicadas are typically darker than annual cicadas, sometimes being black. Periodical cicadas are only found in North America, and are aptly named, as they are a phenomenon that is experienced only every 13 or 17 years. Maturing underground with depths reaching up to two feet deep, periodical cicada adults emerge in large numbers and can be shocking to see. While the cicadas are 13 or 17 years old when they emerge, they will only last four weeks once they leave the ground.
Periodical cicadas have many predators, including birds, rodents, snakes, lizards, fish, raccoons, cats and dogs, opposums and other mammals eat cicadas while they are abundant. Their species survival is called predator satiation, and relies on the large number of their population to be released at selected times in order to sate predators in a way that distracts them from the cicadas which are able to lay eggs. Think of it as a “safety in numbers” strategy.
Given their feeding behavior, despite their foreboding presence, they do minimal damage to plants and trees. The bulk of the damage done by cicadas is to new or young trees whose branches are not yet developed enough to handle the weight of masses of cicada eggs that are left on them.
Locusts are a type of grasshopper and are therefore more readily recognized by their behavior instead of relying on body characteristics. Most grasshoppers are solitary and placid. The swarming behavior is a response to overcrowding of the grasshopper population. With such dense numbers, there is less space to move and increased tactile stimulation of their hind legs causes an increase in the production of the chemical serotonin in their bodies. This increase of serotonin causes the locusts to change color, often shifting their color scheme to yellow and black, eat more, become more aggressive, and breed more readily. This mutation can occur in a timeframe of as little as two to three hours.
Locust swarms can cover great distances and are easily tracked because of the visual created by such large numbers. In 1954, a swarm was tracked which originated in Northwest Africa and migrated all the way to Great Britain.
Unlike cicadas, which drink the juice from plants, locusts eat plants at accelerated speeds. This can be devastating to crop farmers and the community members that rely on those crops for jobs and food. A locust swarm can be 400 square miles in area, and contain up to 80 million locusts into just one half of a square mile. Similar to the behavior of humans shopping while preparing for an emergency, this feeding frenzy is a type of panic response. The overcrowding that changed the swarm from grasshoppers to locusts informs their interaction with crops and they fear food shortages, driving them to eat as much as quickly as possible. Locust swarms are found all over the world and the physical characteristics can shift depending on the climate and landscape.
Scientists speculate that the swarms could serve as a survival mechanism meant to help avoid predators, by appearing to be a large cohesive unit. Spiders, birds, lizards, and foxes are all natural predators to grasshoppers and locusts, but the swarms naturally ward off much opportunity.