YAMAGUCHI (Kyodo) The number of an endangered dragonfly known for the golden crests on its wings has tripled since 2003 in one of its habitats -- thanks to the city of Ube, Yamaguchi Prefecture.

There were 50 of the 4- to 5-cm-long dragonflies during a count last year, after numbers fell to as low as 18 in 2003 at a reservoir in the city where construction work was under way.

The dragonflies, known by the zoological name Libellula Angelina and called Bekko Tombo in Japanese, inhabit ponds with clear water, light reeds and grassy surroundings.

The number of the dragonflies totaled about 300 in 1998, helped by the once favorable atmosphere around the reservoir, which was dug in 1829 for agricultural use.

Prompted by the decline noted in 2003, the city government started efforts to prevent the dragonfly's extinction by mowing excessively dense grass in the area.

This is the first case in Japan that the number of the rare dragonfly has grown due to environment protection measures.