Mai Po Wildlife

Invertebrates

Species of Interest - Four-spot Midget Mortonagrion hirosei

© Katherine Leung / WWF Hong Kong

Physical Description

A small black damselfly less than 2.5cm in length, with four distinctive apple green spots on the back of its thorax. Female Four-spot Midget can be one of two colour patterns: the four-spot morph and the orange morph. Freshly emerged adults are greyish in colour, but the four spots on its back are still visible as they are paler than other parts of the thorax.

Global Status and Distribution

The Four-spot Midget is listed as a vulnerable species on the IUCN Redlist. It was first discovered in a brackish water reedbed in Japan followed by Hong Kong and more recently Taiwan. It seems likely the species also exists in Mainland China.

Despite the discovery of populations in new places and an improvement to its conservation status, the Four-spot Midget is still under threat. In Japan, there has been a reduction in the damselflies preferred habitat type (reedbeds), and potentially suitable areas in Mainland China are being lost to city development, reclamation and dam construction. Intensive research projects and habitat (reedbed) re-establishment programmes are being carried out in Japan on the Four-spot Midget are at least increasing our understanding of the species.

Local Status

The Four-spot Midget has been recorded from 6 locations in Hong Kong. These are mainly coastal marshes at the north-east New Territory including Luk Keng, Nam Chung and Sha Po and at the north-west side – Mai Po Nature Reserve.

Within Mai Po, Four-spot Midget have been observed in reedbeds, on vegetated bunds of both freshwater pond and brackish gei wai and in the inter-tidal mangrove. More than 20 individuals were seen inside the inter-tidal mangrove in a single day, being the highest day count for the species in the Reserve.

Basic Ecology

The Four-spot Midget has a high tolerance to salinity and is usually associated with brackish water wetland habitats including reedbeds, marshes, paddy fields and mangrove. Its main flight period is from March to October and adults prey on smaller flying insects like midges (Chironomidae) and mosquitoes (Culicidae).

Within the WWF Mai Po Management Plan the Four-spot Midget has been highlighted for further research. Projects will be set up to investigate the distribution and abundance of this damselfly so that a management strategy can be formulated.