Why locust swarms seem to hit those who are already suffering the most

With a swarming locust consuming its own bodyweight in food every day, the many-tonne swarms can utterly destroy a farmer's livelihood. But why is it that they seem to target farms that already aren't doing well?

According to new research, it all comes down to nitrogen. The Oedaleus asiaticus in Northern Asia strongly prefers foods with low protein and high carbohydrate content, which are plants that grow in soil with low amounts of nitrogen. This runs counter to much of the accepted wisdom, that high nitrogen/high protein plants would be preferable to the insect, because it would allow them unfettered growth.

Swarming locusts seem to much prefer plants grown in low nitrogen soil — which can be caused by erosion, overgrazing, and overfarming. Places where the farmers can't afford fertilizer, where bad weather has destroyed topsoil, or with a large amount of livestock suddenly become major targets. In fact, for Inner Mongolia, the paper says:

The hypothesis that low plant N can stimulate locust outbreaks is also supported by observations that O. asiaticus population explosions occur exclusively in pastures heavily grazed by live- stock.

What this also means is that there's a potentially straightforward way to lessen the impact of locusts. If an emphasis is placed on maintaining nitrogen levels — through traditional crop rotation, fertilization, or moving grazing stock more readily — it could lead to massive drops in the damage caused by the insects. The researchers even note that nitrogen fertilized plants significantly cut the insect's lifespan. If this same principle holds true for more locust species, it might be the start of a major change in fighting the destruction they cause.

Photo courtesy of Arianne Cease