The Run for Life
Like a biblical plague, millions upon millions of bodies roll forward, those who weaken are mercilessly torn to pieces and destroyed by cannibalistic comrades. Insect-style apocalypse? An image of hell? No, actually, American Mormon crickets are just following their natural foraging instincts.
When insects show up in droves, the human viewer often thinks of motifs from the religious founding books of mankind. Even today, mass incursions of African migratory locusts in search of fresh green are still too reminiscent of a much-quoted passage from the Old Testament, where hungry weeds devoured the whole of Egypt as a kind of divine punishment.
The Mormon crickets (Anabrus simplex) from western North America are not a completely different sight when they travel by the millions, as they do every few years. They march forward unstoppably - no road, no stream, no mountain and certainly no birds or other predators will stop them. As well, because with population densities of more than 100 individuals per square meter and troop lengths of more than one kilometer, almost every countermeasure is in vain.
But what drives these animals – which, contrary to their name, do not belong to the crickets but to the grasshoppers – forward? What makes them ravage entire crops and leave gardens plundered? It cannot be mere hunger, because they are extremely selective in their meal and affect the quality and nutritiousness of pasture land for cattle at most marginally: what is reminiscent of relatively difficult to digest grasses is ignored by the travel-loving insects. On the other hand, they will devour anything that promises some kind of rich protein-such as seed pods, flower petals, carrion, or even animal feces-or might satisfy s alt needs like urine-soaked earth.
This strange observation was enough of a spur for biologists led by Stephen Simpson of the University of Sydney to delve deeper into the migratory behavior of Mormon crickets. They therefore placed various feed samples of different nutritional values - each high in protein or carbohydrates - in front of an approaching army of locusts and observed the corresponding reactions of the animals.
The effect of moist cotton balls with different s alt contents was also tested; also how the hikers deal with immobile Mormon crickets that for some reason would not or could not continue walking. Because until now it was only known that the animals did not shy away from cannibalism if the opportunity arose. So far, however, the trigger for this has eluded the scientists' knowledge - as a result, they placed individuals on the route forcibly shut down because they were stuck and also removed one or both of their hind legs from particularly unfortunate creatures.
After the legions had passed through, the researchers then checked the bait laid out. And lo and behold: As with naturally grown food, carbohydrates were spurned, while protein bombs were gladly taken. Pure drinking water was also rejected, but the hikers were happy to drink liquids containing s alt. The biologists suspect that this greed for s alt and proteins, which has now been documented, is also the ultimate motivation for the cannibalistic activities of the Mormon crickets: Within just 21 seconds, the marchers attacked freshly killed conspecifics and ate them without exception – they make a good s alt - and protein depot that should not degenerate.
In contrast, living and therefore still mobile individuals took a full 165 seconds to attack. And of the 14 intact crickets, 13 managed to survive for more than two hours until they were freed from their predicament by the researchers - the animals fended off attacks by their opponents with powerful kicks of their jumping legs. However, the survival rate of the journeymen with amputated legs, who could no longer use this defensive weapon to its full extent, fell accordingly: If one foot was missing, only eleven of the 14 test subjects survived; if both were removed, then only five of them managed to do so 14.
Simpson and his colleagues therefore suspect two decisive criteria as the initial spark for the long march of the Mormon crickets: They set off when their original homeland only offers insufficient sources of s alt and protein because they have been overexploited accordingly. And once the animals are on the move, it is not advisable to stop, otherwise everyone can become a victim in a short time - movement as self-protection.
That's why (almost) nothing stops the animals anymore, they decided to leave. Then only God's help will help the plagued residents - or at least that of his envoys. Accordingly, the Mormon cricket is named after the Mormon faith group who were the first to document the locusts' rampant migratory drive as they headed toward devastating the crops of Utah's settlers. Legend has it that only the unexpected appearance of numerous kerfe-eating seagulls put an end to this spook and saved the Mormon mission.