By Nicholas Walton BBC News, Zagreb

The bees are trained to associate explosives with food

"We started this because our citizens are exposed to serious risks with mines," explains Professor Nikola Kezic, as honey bees buzz around his head.

"Luckily we also have a long tradition of keeping bees and making honey. Our solution makes use of what we have."

Croatia, like Bosnia-Hercegovina and the other countries of the former Yugoslavia, has a big landmine problem, inherited from the wars of the 1990s.

More than 1,000 sq km (380 sq miles) of Croatian countryside are thought to be contaminated by the mines.

About 250,000 mines are still buried, and more than 100 people have been killed by them in Croatia since 1998.

Lure of food

Removing mines is slow and very expensive. And even after the de-miners have done their work, some may remain in the soil.

Field testing is the next step after trials in the tent

Training the bees to find mines takes place in a large net tent pitched on a lawn at the university's Faculty of Agriculture.

A hive of bees sits at one end, with several feeding points for the bees set up around the tent.

But only a few of the feeding points contain food, and the soil immediately around them has been impregnated with explosive chemicals.

The idea is that the bees' keen sense of smell soon associates the smell of explosives with food. So far this has proved successful.

Prof Kezic says bees can quickly be trained to detect explosives

The first day or so is spent in the large net tent, getting the bees used to associating the smell of TNT with food.

After that several bees are taken out of the colony and tested to see if they react correctly when presented with extracts of explosives.

"This year our work is to increase the bees' sensitivity to the smell of TNT," says Prof Kezic. He warns that it will take time before they are sure the system is reliable enough to use properly.

Painstaking method

Once the technique has been shown to be reliable, the idea is to use the bees on areas that have already been de-mined.

Parts of Croatia are still littered with mines laid in the 1990s

The bees will be expected to settle on areas of ground that smell of explosives. If they land on an area where no landmine was discovered earlier, the de-mining team will investigate to make sure they have not missed one.

If the technique proves a success it might provide a cheap and easily available resource for de-mining teams all over the Balkans.

Other animals have been used before to detect explosives.

Gambian giant pouched rats are used in several African countries, including Mozambique, to find mines. Like the bees in Croatia, they are trained to associate the smell of TNT with food.

Dogs are also used to find landmines and to sniff out hidden explosives, for instance in airports. But unlike rats and bees, the weight of sniffer dogs means that they can be at risk of setting off the mines they are trying to detect.

Dogs have also been used for offensive operations in wartime. In World War II the Soviet Red Army trained dogs to run underneath enemy tanks. The dogs had petrol bombs strapped to their backs which ignited when they knocked against the enemy vehicles.

In the Croatian countryside bee-keeping has been popular for centuries. Delicious pots of honey and other produce can be bought directly from the bee-keepers at roadside stalls all over the region.

Despite many years of working with bees, Prof Kezic has not lost his enthusiasm for them. His office, full of charts, diagrams and models of bees, is testament to his interest in these social insects.

And in his fridge there is further evidence of what makes bees so special: pots of honey and some delicious honey-flavoured raki, the local strong alcohol.