Tiny piece of wire shows how the butterfly makes a beeline for its dinner

Their movements around the garden seem no more than delicate, random meanderings but butterflies can spot promising areas for nectar from up to 200 metres away and can purposely avoid places unattractive to them.

Their movements around the garden seem no more than delicate, random meanderings but butterflies can spot promising areas for nectar from up to 200 metres away and can purposely avoid places unattractive to them.

Using radar tracking devices which are attached to the insect's back, scientists at the Rothamsted Research Institute in Harpenden, Hertfordshire, yesterday said they had become the first to plot the exact path of butterfly flight.

Transponders - 16mm pieces of wire weighing just 12 milligrams (less than 5 per cent of the insect's weight) were attached to 30 peacock and tortoiseshell butterflies, enabling their movements to be plotted accurately, via a radar dish, from up to one kilometre away.

Scientists had previously monitored butterflies by the naked eye - impossible from more than 100 metres - or by marking and collecting butterflies, a technique that only tells researchers if a butterfly is in an area and not why or how it got there. But by use of the transponders, a radar tracking team relayed specific location details to field researchers who found themselves able to keep up with the butterflies as they fluttered through a field. The insects were found to be undertaking fast, directed flights to potential feeding sites. While between foraging missions, they undertook looping "orientation" flights.

"Though this does not establish what is going on in their brains, it does show how butterflies can see a potential area of forage and decide if it looks familiar or suitable," said one of the researchers, Lizzie Cant. "They are intent on reaching forage and not just blown in by the wind."

The harmonic radar technology used to track the butterflies was developed to observe the tsetse fly in Africa, then used by Rothamsted scientists to observe bee flight in the UK. Its application to monitor the flight patterns of a butterfly is compared by Rothamsted to watching the moving "blips" on a ship's radar screen. Attaching the transponder is a delicate process, involving the removal of fine "hairs" on the creature's back, applying a thin layer of paint onto which the transponder - mounted on a sticky pad - can be applied.

Ms Cant said the research would enable conservationists to protect butterflies which, along with bees, were important pollinators of wild flowers. "Butterflies provide a crucial service to plants in many ecosystems," said Ms Cant. "This research will help us to understand a little more about how they survive in a countryside that is becoming more and more fragmented."