Is There a Difference Between a Cicada and a Locust?
In spring and summer when insects become active once again, two bugs that we sometimes hear about are cicadas and locusts (especially when there's a significant "swarm" expected). Sometimes, people use the two words interchangeably for the same insects. Is this acceptable, or is there a difference between a cicada and a locust?
Yes, there is a difference between a cicada and a locust.
Cicadas and locusts are in fact different insects. They aren't even from the same order. They are often confused with each other due to their behavior. Locusts swarm, and periodic cicadas are often thought to swarm. However, cicadas don't actually swarm - they just happen to be above the ground in large numbers at the same time. The association between cicadas and locusts goes back to colonial times. When periodical cicadas showed up in large numbers, the colonists assumed they were experiencing a "locust plague", similar to the ones in the Bible.
What's a locust?
A locust is a type of grasshopper from the family Acrididae. These insects do in fact swarm when they reach adulthood, and they cause significant damage to crops and fields (even as nymphs). The only distinction between a locust and a non-locust grasshopper is the swarming behavior. Locusts don't always swarm, however. They do so after periods of wet weather, which leads to areas of overcrowding (when the plants begin to die, the locusts all make their way to the remaining food). Then, the insects bump into each other and activate hormones. The hormones cause them to change color, breed even more, and synch up their growth and egg-laying. When they run out of food in their area, they'll all fly together in a swarm to find something else to eat. They can travel up to 100 miles each day.
What's a cicada?
A cicada is an insect from the order Hemiptera and superfamily Cicadoidea. There are over 2,500 known species of cicadas, and they live throughout much of the world. Cicadas spend most of their lives underground, where they live off the xylem of plants. When they come close to the end of their lives, they emerge from the ground to mate. Adult cicadas are most recognizable by their prominent eyes, and many species have transparent wings. Each cicada species has its own mating song, which is "performed" by the males using structures called tymbals. Some cicada songs can be as loud as 120 decibels, which puts them among the noisiest insects. This loud noise has an added benefit for the cicadas - it keeps away predators such as birds.
Are there different types of cicadas?
Some cicadas are annual and show up every year, and others (the ones that are often confused with locusts) are periodic. Annual cicadas are also known as "dog day" cicadas, since they are most common during the "dog days" of late summer. They're greenish in color, can be as large as 2 inches, and are heard more often than they're seen. They have a lifespan of 2 - 5 years.
Periodical cicadas are the ones most often mistaken for locusts. They show up earlier in the year than annual cicadas - in spring when the temperature of the soil at 8 inches below ground reaches 63 degrees Fahrenheit. Their lifespan is 13 or 17 years, and the cicadas in a particular region that have their life cycles synched are grouped into a "brood." An example of this is "Brood II", which is due to emerge in much of the East Coast in 2013. When millions of cicadas are active at the same time, it can certainly seem like a swarm.
Unlike locusts, cicadas don't destroy crops. They don't sting, and they generally don't bite. However, they have been known to mistake a human for a tree, and it hurts if they poke you with their proboscis while looking for food. Even though they generally are not harmful, they can be annoying to many people, mainly due to the noise. Due to the huge numbers of cicadas that are active at once, the sound of a cicada invasion can be deafening. Those who live in an area with an emerging brood may wish to consider using earplugs or noise-canceling headphones during the weeks the insects are active.
References and more information
Questions & Answers
What do cicadas eat?
Cicadas feed on the xylem, or fluid, of trees and shrubs.