Orb-weaver spiders may manipulate their prey's behaviour to help them attract more prey to their webs, according to a new Current Biology study.

This is the first time we've seen spiders use such manipulative techniques to get their dinner.

An orb-weaver spider grapples with a firefly caught in its web. Credit: Xinhua Fu

It's almost sunset in the paddy fields of Wuhan Province, China, and, as they do every evening, orb-weaver spiders (Araneus ventricosus) are starting to build their webs.

At the same time, fireflies (Abscondita terminalis) are beginning to flash in the fading light, with the aim of attracting mates. Females emit single flashes to attract males, while males emit multiple flashes to attract females.

Orb-weaver spiders eat fireflies, but only the males. This is because only the males can fly and therefore get trapped in webs.

During a recent study of the region's bug life, a team of scientists noticed something strange, though. The spiders didn't always eat the male fireflies straight away. What's more, male fireflies caught in webs seemed to flash in an odd way, almost as if they were flashing like females.

There's an obvious advantage for the spiders when trapped male fireflies flash like females – other males will come to the web because they think they are flying to a mate, which means more food for the spider. But the scientists wanted to test if this was really happening, and if it was, whether the spiders were causing the change in the male fireflies' flashes.

And so, armed with video cameras and notepads, the scientists began their experiment to test whether the spiders were manipulating the behaviour of their prey.

As the researchers suspected, trapped male fireflies did indeed flash like females. What's more, when a spider was present in the web with the male, a higher number of male fireflies flew to the web. These results suggest that the spiders really were manipulating the trapped male fireflies so that more males would fly to the web.

But how were the spiders changing the behaviour of the fireflies?

The spiders would usually bite the fireflies when they became trapped in the web, and the team suggests that their venomous bite might somehow cause behavioural changes in the fireflies.

How exactly this might work is currently unclear, but the team are hoping to shed some light on it. "We will explore the mechanism behind spider manipulation," Professor Daiqin Li, behavioural ecologist and an author of the study, tells BBC Wildlife Magazine.

Professor Li says they are also interested in exploring whether related spider species, some of which feast on fireflies too, might manipulate their prey in a similar way.