Serotonin Changes Locusts From Shy Loners to Swarming Pests

By Eliza Strickland | January 30, 2009 8:52 am

locustsLocusts are prompted to band together in enormous, destructive swarms by the same brain chemical that is linked to happiness in humans. A fascinating new study has found that locusts that are about to swarm experience a sudden surge of serotonin, the same neurotransmitter that’s targeted by antidepressant drugs. “Here we have a solitary and lonely creature, the desert locust. But just give them a little serotonin, and they go and join a gang,” observed Malcolm Burrows [AP], one of the study’s authors.

Researchers say the findings may lead to methods to block the formation of locust swarms. These infestations, which can cover hundreds of square miles and involve billions of vegetation-munching insects, can devastate agriculture and cost tens of millions of dollars to control [The New York Times].

Because locusts usually avoid each other, it’s only dire circumstances that bring them together in buzzing hordes. For instance, unpredictable desert rains cause vegetation blooms, which in turn makes locust populations skyrocket. But as the rains abate and fertile land shrivels up, locusts crowd together in the remaining green patches. Eventually, the swarm trigger goes off and the locusts take to the skies—”a strategy of desperation driven by hunger,” [National Geographic News], says coauthor Stephen Rogers. When they make that behavior shift they also change appearance dramatically, going from light green to dark brown.

In the study, reported in Science [subscription required], researchers were studying the changes in locust behavior and tested them for a variety of chemicals. The only change they found was that when the insects were swarming, they had about three times more serotonin in their systems than when they were living as solitary creatures. So the scientists took some solitary locusts and injected serotonin into them. Sure enough they changed in appearance and flocked together. The Dr. Jekyll to Mr. Hyde transformation took only a few hours [AP].

The researchers also investigated what conditions spurred the serotonin surge, and found that the sight, smell, and touch of other locusts when the insects are crowded together are all cues. Indeed, the scientists found that tickling the insects’ back legs for a couple hours could induce the locusts to make more serotonin [AP], because they interpreted that stimulus as the jostling of other insects. Finally, when researchers injected a serotonin-blocking drug into locusts in a crowded enclosure, the insects didn’t change color and showed no inclination to swarm.

Related Content:
DISCOVER: Hunger on the Wing
DISCOVER: Locust Plague Sweeps Across Africa

Image: Tom Fayle

  • Rosiecee

    It is interesting that the locusts become less of a loner type and more aggressive. This happens also in humans when they are exposed to antidepressants, especially the antidepressants known as SSRIs.

    Go to where there are over 2,800 cases, with the full media article available, involving bizarre murders, suicides, school shootings [47 of these] and murder-suicides – all of which involve SSRI antidepressants like Prozac, Zoloft, Paxil, etc, . The media article usually tells which SSRI antidepressant the perpetrator was taking.

  • nick

    Okay, you know how we’re totally trying to grow bio-engineered crops with drugs in them? Grow bio-engineered crops that have anti-serotogenic drugs in them – then when the swarm descends on your crop, it’ll eat a short meal, come down off serotonin, get bored and wander off, no longer swarming.

  • Eric

    and then we eat the the same crops and have our minds completely drugged also. Great idea Nick.

  • Rob

    I get depressed and hungry just thinking about such Frankenfood. But anybody noticed that ecstasy driven Raves and Plagues of Locust have the same trigger – over stimulation of serotonin? Metaphorically tidy at least… Maybe a new bio weapon, spray ecstasy all over the little buggers, a good supply of which can be confiscated from any give swarm of Ravers…

  • Jeff

    Nick not sure how well that would working seeing as the food is meant to be consumed by people, unless of course you agreed to take my portions : )

  • KK

    An interesting note is that locust is actually a food source for certain cultures. So this might be a safe way to use this fact to help improve harvest of locusts (and subsequently improve in controlling their number).


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