Just add water The garden insect that can turn into a plague Jeffrey A. Lockwood
The ravenous swarm stretches
as far as the eye can see.
It has no commanding general
or strategic plan;
its only goals are to eat, breed,
and move on—
a relentless advance that transforms
pastures and farms into barren wastelands.
These are desert locusts—
infamous among their locust cousins
for their massive swarms
and capacity for destruction.
But these insects aren’t
always so insatiable.
In fact, most of the time desert locusts
are no more dangerous
than garden-variety grasshoppers.
So what does it take to turn
these harmless insects
into a crop-consuming plague?
Desert locust eggs are laid
in the damp depths of desert soil,
in arid regions stretching
from North Africa to South Asia.
During the dry weather
typical in these ecosystems,
desert locusts live a solitary lifestyle.
Adolescent hoppers will spend
a few lonely weeks foraging for plants,
before growing wings,
reproducing, and dying.
But when a region receives
an abundance of rain,
the scene is set
for a startling transformation.
Increased moisture supports
more vegetation
for newly hatched hoppers to eat,
leading large groups to feed
in close proximity.
The frequent contact stimulates
their leg hairs,
triggering the release of a hormone
that causes them to actively cluster
even closer.
Gluttonous crowds of locusts
produce huge amounts of poop,
which carries a pheromone that furthers
their transformation.
The hopper’s diet shifts to include
plants with toxic alkaloids.
Soon, the locusts take on a striking
pattern that warns predators
of their newly poisonous nature.
Smaller groups merge
into bands of millions,
which mow down virtually all plant life
in a kilometer-wide swath.
Roughly every week they shed
and expand their exoskeletons,
growing to roughly 50 times
their hatching weight in just one month.
Finally, the metamorphosis is complete.
The adults beat their translucent wings
and take flight
as a full-fledged locust swarm.
In this gregarious phase, these
long-winged, brightly colored creatures
appear so different
from their solitary counterparts
that they were long thought
to be a separate species.
A typical swarm contains more locusts
than there are humans on the planet,
covering hundreds of square kilometers
in a dense cloud.
At these numbers, desert locusts
easily overwhelm their predators.
A large swarm can match the daily food
intake of a city of millions,
and flying with the wind,
the insect invasion can travel
up to 150 kilometers a day.
This living tornado can also
cross large bodies of water.
In 1988, a swarm even managed
to traverse the Atlantic Ocean.
The locusts likely formed rafts to rest
at night,
before fueling up in the morning with
a nourishing breakfast of their dead kin.
While flying over land,
they seek out moist soil to lay eggs.
Swarming mothers transfer their gregarious
condition to their offspring,
making it likely that the next generation
will form another swarm.
This means that while an individual
desert locust lives only three months,
a plague can last up to a decade.
The potential for a years-long plague
isn’t unique to desert locusts,
but the region they inhabit makes
the prospect particularly deadly.
Their habitat spans
some of the world’s poorest countries,
largely populated by people who grow
their own food.
By consuming crops and pastures,
these insects directly endanger
10% of humanity.
Fortunately, a desert locust plague
doesn’t last forever.
When a wet period ends,
vegetation becomes scarce
and egg laying conditions decline.
As existing swarms die off, new hatchlings
spread out in search of food,
creating enough distance to prevent
solitary locusts from transforming.
Human intervention can also help.
Researchers use satellite imagery
to identify regions at risk
of becoming locust hotspots
and alert local governments.
While most countries fight back
with chemical insecticides,
some regions have found success using
fungal diseases that are lethal to locusts
but safe for people and the environment.
Unfortunately, other modern practices
are exacerbating the threat.
Fields densely packed with a single crop
are like a table set for locusts.
And erratic weather caused by climate
change makes swarms harder to predict.
If we plan to discourage lonely locusts
from becoming catastrophic crowds,
humans need to cut carbon emissions,
rethink our agriculture,
and generally reconsider
our own ravenous appetites.