Carnivorous plants conjure up all sorts of terrifying imagery, thanks in large part to productions like Little Shop of Horrors. They’re seen as unthinking, vacuous bottomless pits, consuming anything and everything that comes their way. Well, the “unthinking” part might be technically true, but researchers at Bristol University have found that at least when it comes to pitcher plants, some finesse is involved in tricking their prey.

The pitcher plant’s mechanism is pretty basic: The plant produces nectar that attracts ants. The ants approach the nectar but fall victim to the plant’s slippery inner surface, which causes them to fall into the plant’s base where enzymes await to slowly digest them. Come for the sweet meal, stay for the grizzly acidic death. However, the plant has some tricks up its sleeve with regards to exactly when the surface is slick.

“The plant’s key trapping surface is extremely slippery when wet but not when dry.  For up to eight hours during dry days, these traps are ‘switched off’ and do not capture any of their insect visitors.  At first sight, this is puzzling because natural selection should favour traps that catch as many insects as possible,” explained lead researcher Dr Ulrike Bauer.

Though the straightforward approach seems to make more sense, experiments reveal why it doesn’t. The researchers observed the plants tended to capture large batches of ants of the same species, so they caused some plants to be artificially slippery all the time. They found that those plants didn’t capture ants in the same groupings as the unfettered ones, instead pulling in random assortments of insects.

It turns out that being too greedy actually hurts the plant in the long run. Ants, being relatively intelligent social insects, use scouts to suss out everything from potential building sites to new food sources. Were the plants to stay slick all the time, the scouts would never return to the colony and would therefore never bring with them an even larger corps of potential ant meals.

“By ‘switching off’ their traps for part of the day, pitcher plants ensure that scout ants can return safely to the colony and recruit nest-mates to the trap.  Later, when the pitcher becomes wet, these followers get caught in one sweep.  What looks like a disadvantage at first sight, turns out to be a clever strategy to exploit the recruitment behaviour of social insects,”  Dr Bauer said.

How the pitcher plants have the wherewithal to make the switch is as-yet unknown.