In a scene that was equal parts futuristic and biblical, a swarm of grasshoppers descended upon a giant pyramid in Las Vegas this weekend. Meanwhile, a true plague descended upon Yemen’s largest city, enveloping it in swarm of locusts. Each infestation will have very different consequences for the people living through them, but in both cases, it’s shaping up to be a very swarmy summer.
On the surface, these events bear one major resemblance: a large swarm of insects descending upon a human settlement. But there are some basic biological reasons why they differ. The Vegas swarm is a massive cloud of grasshoppers, whereas the Yemen swarm is a swarm of locusts.
The difference between locusts and grasshoppers is tricky but can be boiled down to a simple rule: all locusts are grasshoppers, but not all grasshoppers are locusts.
The Difference Between Locusts and Grasshoppers
A locust is a species of short-horned grasshopper that is capable of existing in either a solitary or highly social “gregarious” (that’s the scientific term) state.
Under certain environmental conditions, these normally solitary insects undergo physical and behavioral changes that mark their transition into gregarious locusts. They get darker (physically), begin to swarm, and become far more mobile. Desert locusts, for instance can fly between 5 and 130 miles in a day and have been known to cross the Red Sea.
The transition is a nice example of phenotypic plasticity, an organism’s ability to adapt its external appearance in response to the environment.
Locusts’ ability to transform is technically called “density-dependent phase polyphenism,” which means they can change their appearance depending on how many of them are around and in close contact with one another.
Notably (and somewhat confusingly), other, non-locust grasshopper species can also swarm, as the Las Vegas infestation shows.
Why Locusts and Grasshoppers Swarm
Some research suggests that overcrowding triggers a genetic response in the locust’s body that marks the beginning of the transformation into the gregarious state. Biochemically, that process may include the release of serotonin, as a team of scientists at Cambridge University demonstrated in 2009.
But for that to happen, something has to cause that overcrowding to start with.
Uncharacteristically heavy rain has been implicated in the Yemen locust infestation. According to a report from the Food and Agriculture Organization of the United Nations (FAO), heavy rainfall is helping them breed, increasing population density.
Wet weather is also being blamed for the swarms of grasshoppers in Las Vegas.
Jeff Knight, an entomologist at the Nevada Department of Agriculture, assured the The New York Times on July 27 that the Las Vegas-based swarm, which he says may last weeks, is not hazardous. People aren’t thrilled about them, he noted, but they won’t cause any lasting harm: “They don’t bite. They don’t sting. People don’t like them. That’s understandable.”
Meanwhile, across the world in Yemen, the FAO has issued warnings for large swarms of locusts that are sweeping the area and destroying crops, despite interventions to control them. Twitter videos show massive swarms descending upon the nation’s largest city, Sana’a. According to local reports, some people met the swarms with open nets, preparing to fry them up for a quick meal. The effects on local farmers, however, has been far more negative.
“All our crops were horribly damaged,” a farmer from the region told The National. “We stood helpless because we had nothing [we could do]… Alas, everything is gone.”
The locust swarm in Yemen swarm is a serious concern. The Las Vegas swarm, on the other hand, may seem similarly plague-like, but for most people passing by the Luxor pyramid, the similarities are just surface-level.