Locusts are just certain kinds of migratory grasshopper - but in large enough numbers, these bugs go bad. With the right weather and plenty of food, their population booms and those harmless hoppers change. They develop longer wings, a black and yellow color scheme and a ravenous appetite... and then they swarm
Let's take a look at...
- How Harmless Grasshoppers Become a Plague: What starts a swarm?
- Controlling the Swarm: What can we do about them?
- Cannibals Driven by Fear and Hunger: What keeps a swarm moving?
- An Edible Threat: Are there uses for locust swarms?
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| Locusts can eat their bodyweight in food each day... (abel12579) |
How Harmless Grasshoppers Become a Plague
Locust swarms aren't a thing of the distant past. Between 2019 and 2022 a massive outbreak struck East Africa, the Arabian Peninsula and the Indian subcontinent.
Sure, we have technology and pest control methods that our ancestors did not... but a swarm can cover an area the size of a city and can travel 100 miles in a single day. Infestations can also multiply at a horrifying rate - each locust generation can be 20 times the size of the last. The 2019-2022 outbreak was the worst to hit East Africa in 70 years - and that's because it takes very specific conditions for locust populations to spiral out of control.
The average locust prefers being solitary (and for good reason - more on that later) but if presented with an abundance of food and wet, sandy soil in which to lay eggs, their population can explode. Get enough of them in the same place and both their behavior and physical form will change.
Researchers found that tickling the back legs of locusts (faking being jostled by companions) floods them with serotonin, which seems to act as a chemical signal. The insects become gregarious (more social) while developing longer wings alongside a black and yellow color scheme. They also become ravenous, seeking out any source of food that they can.
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| Pesticides can only do so much... (Eric Brehm) |
Controlling the Swarm
So how much damage can a locust do? Well, a locust on the move can eat their own body weight in food each day. That may not seme like that much, but an outbreak can contain hundreds of billions of the hungry insects.
It's also very hard to stop locust swarms - spraying them with pesticide can make crops unsafe for human consumption... though researchers are looking in to using bioweapons like Metarhizium acridum, a fungus that attacks and kills locusts but seems safe for humans. Some researchers believe sequencing the locust genome could reveal other weaknesses specific to the insects.
Other groups are looking for stranger solutions. A German-designed solar-powered electrical net that can scare off or even electrocute the insects has seen limited testing, though having to manually drag it through crops has disadvantages all of its own.
A lower tech solution is the "hopperdozer" - a wheeled or runner-mounted screen that can be dragged across a field. Insects startled by the approaching contraption jump, hit the screen and tumble into a trough of kerosene and water to die.
There's also the potential of using animals to eat the flying pests. China has used ducks for pest control in the past and contemplated sending 100,000 of the hungry birds against locusts in Pakistan. Apparently a single duck can gobble up around 200 locusts in a single day!
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| Groups of locusts tend to become cannibals... (christels) |
Cannibals Driven by Fear and Hunger
So you might be thinking that hunger drives a locust swarm - that's accurate, but not the whole story. I mentioned earlier that the average locust prefers being solitary... and that's because locusts are cannibals.
A locust is a good source of protein and salt, making them an attractive meal. Solitary individuals avoid much of this risk (you can't be cannibalized if you don't encounter another locust) but that changes during a swarm. The gregarious locust is surrounded by other insects, ones that are biologically hardwired to become ravenous.
Researchers simulated swarms and modeled the chances of a locust being cannibalized. They found that the movement of a swarm dramatically reduced the odds of becoming dinner, with any individual that broke off or fell behind running the highest risk of being eaten.
Locusts also have a fear of being approached from behind by another locust (not surprising really, given the whole cannibalism thing) which can create a feedback loop. A locust will attempt to move forwards to get away from the insect behind it, while the insect behind it will attempt to keep up and thus not fall out of the "swarm" and make a tempting target. Researchers found that cutting the nerves in the abdomen of locusts (making it harder for them to feel the approach of another locust) reduced the amount of group movement and increased the amount of cannibalism!
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| Well, we eat prawns... (Chantal Lim) |
An Edible Threat
It's true that locusts can devastate crops... but the insects themselves are edible.
The insects are used as food (either animal or human) in sixty-five countries and have a surprisingly high nutritional value. They are well suited to human consumption (beating out many traditional meats) but getting people to try entomophagy (insect eating) has its own issues. Researchers have looked into a mixed approach, using ground locusts to enrich bread with promising results. That said, using pesticides can render locusts unsuitable to human consumption.
Even if they don't take off as a foodstuff, locusts are rich in oil and chitin. The chitin (taken from the exoskeleton of the locust) can also be used to make the biopolymer chitosan - a substance that could be useful in both industry and biomedical science!
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