Have you ever witnessed a dragonfly skimming the surface of the water? There is a Chinese idiom metaphorising this behaviour to describe one doing superficial work without attention to detail. This behaviour can be seen in certain dragonflies where they skim over the water and dip the tip of their abdomen into the water effortlessly in the blink of an eye to lay eggs. The hatched nymphs rely on freshwater resources for growth, so you can always spot dragonflies around freshwater habitats such as streams, ponds and marshes.
Contrary to the norm, the Mangrove Skimmer (Orthetrum poecilops poecilops) is a rare exception that inhabits mangroves. They are relatively uncommon in Hong Kong and their populations are mainly concentrated in the northeastern parts of the New Territories. They have also been recorded in Tung Chung and Tai O on Lantau Island. They are often found in mangroves with freshwater inflow. Due to the limited research on this species, their habits and habitat requirements are still baffling us and remain mysteries. For example, it is uncertain whether the nymphs of Mangrove Skimmer can adapt to brackish water in mangroves. It was only in recent years that their nymphs were recorded for the first time in Hong Kong. Their discovery from brackish marshes and mangroves demonstrated their tolerance to salinity and confirmed the importance of mangroves as their living and breeding grounds.
The males of the Mangrove Skimmer have pale blue synthorax and abdomen, which is very similar to another common dragonfly species in Hong Kong, the Marsh Skimmer (Orthetrum luzonicum). However, the Mangrove Skimmer has a signature alternated black and white markings on its forehead, and its first to third abdominal segments are significantly swollen compared to the rest of the segments. In contrast, the Marsh Skimmer lacks such markings on the forehead, and its first to third abdominal segments are not as swollen as Mangrove Skimmer's do. Moreover, the Marsh Skimmer is often found in abandoned paddies and freshwater marshes rather than mangroves. As for the females of Mangrove Skimmer, they differ from the males in colouration and have yellow synthorax and abdomen.
The Mangrove Skimmer is listed as Vulnerable on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. Their habitat requirements are specific, as both adults and nymphs inhabit mangroves. Therefore, they are highly susceptible to the impacts of urban development, pollution and habitat destruction. This highlights the significance of mangrove conservation work for these species that depend on mangroves for survival.
If you wish to catch a glimpse of this dragonfly that resides in mangroves, bring along your binoculars, visit the mangroves in Tung Chung and Tai O from May to August when the weather warms up and try your luck!