Animals
Millions of the bugs, native to the U.S. West, are blanketing sidewalks and devouring vegetation.
ByLiz Langley
Published June 22, 2023
• 5 min read
Hordes of Mormon crickets—technically a type of shield-back katydid and not a cricket at all—have been migrating through Elko, Nevada and other areas of the West in recent weeks, creating a scene like something from a scary movie.
These flightless, thumb-sized, omnivorous cannibals have been covering sidewalks, eating up vegetation and each other. They don’t bite, but they do literally stink.
Len Coop, an entomologist at the Oregon State University describes their fragrance as a “musky, sickening odor,” and notes “they probably smell worse when you crush them because it releases a lot more scent,” an inevitability when they’re covering roads like an undulating carpet.
If you’re driving on a smaller road and your window is down, says Greg Sword, an entomologist at Texas A&M University,“it sounds like you’re driving over bubble wrap.”
(Watch swarms of millipedes join ranks to survive.)
Where did they come from?
Mormon crickets got their name during a mid-19th century migration into the Salt Lake area in Utah where they destroyed the crops of Mormon settlers. As they feasted, they chirped like crickets.
These invaders, though, are not invasive.
“They’re indigenous, native to the Great Basin mountain range system and the high desert of all these western states,” Coop says. They’re successful at these elevations because they tolerate cold temperatures well.
Mormon crickets breed once a year and their eggs, often laid just under the sandy soil, can tolerate below-freezing temperatures. They hatch the following year, or at high elevations where it’s colder, they may hold out for a second year.
After hatching they’ll go through eight growth stages as nymphs. In that stage, they may be solitary, chowing on grasses, shrubs, and herbaceous plants.
But when the population booms and food is scarce, they migrate, moving forward in large masses during the daytime when temperatures are mild and stopping when temperatures fall at night.
The migration changes them from loners to “gregarious,” social insects, Coop says. Young members of the migrating group change color to green, orange, or brown and march together.
Sex roles also change on the road: When the crickets are stationary and food is abundant, the males compete for females to mate with and give a spermatophore, a nutritious package passed along with the sperm during mating, Sword says.
When food is scarce and the crickets are moving, however, females compete for access to the males and this now-valuable nutritional resource for their offspring.
Where are they going?
Mormon crickets don’t have a predetermined destination, like monarch butterflies that migrate from North America to Mexico. They simply keep moving forward in search of food and possibly in order not to get eaten by the crickets behind them. Sword and his colleagues also found evidence in a 2005 study of external factors—such as wind direction or the movement of individuals—changing the direction of the group.
Along the way, they eat a lot of vegetation, including crops, gardens, and rangeland livestock forage. A 1937 infestation caused $500,000 in damages, over $10 million in today’s currency. In 2001, the Los Angeles Times reported $25 million worth of damage to crops including wheat, barley, and safflower.
“They don’t just eat everything down to the ground [on rangelands],” Sword says, but are discriminating, starting with nice, soft seed heads and flowers. However, if they find a farm, like an alfalfa field, they’re an immediate threat to someone’s livelihood.
In addition to providing new food sources, migration provides safety in numbers. Lone crickets are easy targets, but the larger the group the better the chance that a predator will grab somebody else.
Mormon crickets are cannibals
In a 2006 study in the journal PNAS, Sword and his team tried to determine what the insects were looking to eat.
What they were missing in their diet was protein and salt—two dietary needs that can be met by eating their fellow crickets.
“Put two in a bucket, and you’ll only see one in the end,” Sword says. In under an hour, one will have eaten the other.
Their cannibalism is more opportunistic than the result of predatory behavior. If one is injured, it will likely get eaten. They also scavenge their fallen, or squished, comrades.
(Cannibalism in animals is more common than you think.)
Appreciating the spectacle
The bugs haven’t always been considered a headache.
Native Americans appreciated them as a food source, and today, edible insects are increasingly considered a new, sustainable form of protein.
And while they may be a nuisance for many, Sword admires their ability to survive.
“You get these groups of millions and millions of insects all marching across the desert in the same direction in a seemingly coordinated fashion,” he says. “From a science perspective, it’s remarkable.”
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