8 February 2020 | New Scientist | 29Swarm of death
Photographer Ben Curtis
Agency AP Photo
THIS farmer can only watch in
dismay as locusts in swarms of
biblical proportions devour her
crops outside Katitika village
in Kenya. It is the worst invasion
by desert locusts (Schistocerca
gregaria) in decades to hit Kenya,
Ethiopia and Somalia, destroying
crops in an area already facing
food insecurity. Somalia has
declared a national emergency.
Hundreds of millions of locusts
are forming swarms bigger than
cities. Stopping them will require
the aerial spraying of pesticides,
which could cost $70 million,
says the United Nations Food and
Agriculture Organization (FAO).
It fears locust numbers could
grow some 500-fold when rains
arrive in March, bringing new
vegetation. An adult can eat its
body weight in food daily, and a
Paris-sized swarm can eat as much
in a day as half the population
of France, according to the FAO.
Desert locusts are usually
solitary, but rain after drought
can cause a surge in vegetation,
and locust breeding. As the
wingless nymphs, known as
hoppers, get crowded together,
the stimulus of frequent physical
contact triggers changes to
their colour and behaviour.
Hoppers change colour as they
become gregarious. Flying
adults also change colour, turning
pink if immature or yellow if
mature. The locusts here look
immature, so can’t yet produce
a new generation. ❚
Chris Simms