This Bug Only Warns You Not to Attack It After You Attack It

Nuytsia@Tas, Flickr // CC BY-NC-SA 2.0

Rile up a cat and it might arch its back, raise its fur, bare its teeth and start hissing at you. Kitty’s little tantrum is what’s known as a deimatic or startle display, a way of scaring or distracting a threat and buying some time to escape. Lots of animals have their own displays like this. Some are honest warnings about the animals’ defenses (like toxins), while others are just bluffs. Either way, the display only benefits an animal if it scares or stops a predator before an attack. There’s not much use in telling a predator how dangerous you are or trying to scare it off when it’s already chewing on your leg. It would make sense, then, for a startle display to be obvious and come before an attack.

And that’s usually how it works. But not for Australia’s mountain katydid (Acripeza reticulata).

These thumb-sized cricket cousins are slow and clumsy, and defend themselves by secreting bitter chemicals from their abdomens. These chemicals not only taste bad, but are toxic to birds and mammals (but are, oddly, aphrodisiacs for some insects). The katydids scare potential predators and advertise their toxins with a startle display that involves vomiting and flashing the vivid red, blue, and black stripes hidden beneath their dull brown wings. It’s impressive, but to zoologist Kate Umbers, the display seemed to be too little, too late, because it came after the bugs were attacked. 

In the field, Umbers found she could pick the bugs up no problem, and only after she grabbed them did they try to deter her or give any indication that they had other defenses. In this case, that was fine. Umbers wasn’t going to hurt the bugs, after all. But flashing a warning or startle display so late wouldn’t help them if they’d been snatched up in some animal's claws instead of a scientist’s hands.

Umbers was puzzled, and teamed up with Johanna Mappes (who has done some cool work with snakes that I’ve covered here before) to test the defensive reactions of 40 more katydids in the lab. Almost none of them reacted when the scientists blew on them, waved a book over their heads to look like a passing bird or tapped a pen near them. They only flashed their colors and puked when they were prodded or grabbed. 

As counterintuitive as a post-attack startle display is, Umbers and Mappes say it starts to make sense when you think about the katydid’s other characteristics. While most animals would startle a predator and then flee while it was distracted, the katydids can’t really do that. In addition to being slow and clumsy, the bugs can’t jump very far, and only the males can fly. What they do have going for them, though, is their chemical defenses and a set of tough, leathery brown wings that both shield their abdomen and blend in with leaves and stones on the ground. 

The researchers now think that the bug’s display isn’t too late, but just sits in a chain of defenses in a place that breaks with the way nature usually does things. They think the katydid relies on camouflage as much as possible to avoid predators. If it is spotted and attacked, its tough wings help it survive the initial attack and the combination of toxins and startle display deters a second attack. Holding off on the startle display instead of using it earlier like most animals would helps the bug avoid revealing itself to a predator that might not have actually noticed it.

Umbers and Mappes would like to test their hypothesis and see how the katydid’s defense suite fares against real predators, but there’s another problem they’ll have to solve first. No one seems to know what eats these katydids. Umbers did notice lots of ravens and magpies in the areas where the bugs are found, so they’re likely candidates. Both these birds tend to investigate prey with their beaks before chowing down, which would give the bug a chance to flash its colors after initial contact but before it’s really in danger of becoming lunch.