A praying mantis attacking the worm animation (left), flinching (middle) and thrashing at a looming threat having become more aggressive after seeing a passing worm snack (right).
With a pair of beefed-up forelimbs ready for action, praying mantises look as prepared as any prize fighter, but these animals aren't just fighting for glory, the stakes are far higher: they're after dinner. Yet, even mighty praying mantises are vulnerable to larger predators, so there will be occasions when it would be wise to disregard a tasty treat to avoid ending up on someone else's menu. ‘Most behaviour needs to strike a balance’, says Jacob Bosse from Case Western Reserve University, USA. But it wasn't clear how much of an impact prior experience has on a praying mantis's reactions, so Bosse and colleagues, Gavin Svenson, Troy Bowers, Brendan Bourges-Sevenier and Roy Ritzmann (all from Case Western Reserve University, USA), decided to find out how Chinese praying mantises (Tenodera sinensis) responded to a threat after experiencing temptation.
Bosse displayed a tempting worm-shaped blob shuttling back and forth on a screen to provoke praying mantises into an attack and filmed their reactions. Analysing the praying mantises’ responses, the team saw that 30% flung themselves aggressively at the screen to capture the fake feast while 25% were intrigued by the bobbing animation. However, when Bosse and the team tried to frighten other mantises with a rapidly looming blob, 90% of the insects took some form of evasive action, from flinching and turning away, to stepping back; some even fell off their perch. But how would the insects react to the terrifying blob threat when they had just been wound up by a passing worm snack?
The team tempted the praying mantises with the TV worm on a screen before quickly activating the looming spot, and the results were surprising. The insects that had just reacted aggressively to the passing worm were less afraid of the looming threat – a few tried to get out of the way, ∼25% paid little attention, but ∼50% reared up and tried to repel the approaching threat, thrashing at it with their impressive forelimbs. ‘This thrashing response was unique to defensive trials that followed aggressive responses to simulated prey targets’, says Ritzmann. The praying mantises’ prior experiences dramatically impacted their reaction to a scary situation.
The scientists also tested the insects’ responses as they aged and, even though the youngest mantises didn't seem to be too interested in the shuttling worm, the animals became far more aggressive in middle age (11–25 days), enthusiastically assaulting the screen worm, before becoming mellow again as they aged. Ritzmann explains that this increase in the animal's aggression levels, especially the females’, is probably related to their time of life. ‘Middle age, when the mantises – in particular females – were most aggressively attacking prey, is when they were developing egg cases and probably needed more food’, he explains. In addition, the males were more passive than the females.
Finally, the researchers compared the reactions of wild praying mantises, caught on the Case Western Reserve University campus, with those of lab-reared animals – which had never faced a predator in their lives – and found the wild animals launched themselves aggressively at the passing animated worms without a second thought. ‘When they made the decision to attack, they tended to go right to it without dilly dallying around’, chuckles Ritzmann. In contrast, the insects that were reared in the lab seemed to ponder their lunch before attacking. ‘A lot of neuroethologists have told me anecdotal stories suggesting that lab-reared insects are more docile than wild caught, but this may be the first paper to actually test this’, says Ritzmann.
