Dragonflies: Hong Kong's Vibrant Guardians Against the Mosquito Menace

An ancient predator hunts in the streets and wilderness of Hong Kong. With a lineage stretching back some three million years, these stalwarts of time remain almost unchanged from the era of the dinosaurs! Yet, we hardly seem to notice them, even when they pass by us in plain sight.

Don’t let their tiny stature fool you though, for these winged jewels of the city actually provide a highly valuable service to us humans!

As one of nature's most effective hunters, dragonflies, and even their larvae, predate heavily on mosquitoes!

In fact, according to a 2023 study conducted by the Journal of Animal Ecology in conjunction with the British Ecological Society, there is "strong evidence that dragonflies/damselflies can be effective biological control agents of mosquitoes, and environmental planning to promote them could lower the risk of spreading mosquito-borne diseases in an environmentally friendly and cost-effective manner."

Dragonflies are essentially mosquito assassins, so if you see one in the wild, be thankful that these gorgeous insects help control diseases like Dengue Fever from rampantly spreading!

1. Eye on the Prize: A dragonfly's head is mostly dominated by two massive eyes. These compound eyes consist of up to 30,000 individual lenses (ommatidia), providing nearly 360-degree vision and allowing them to detect movement from almost every angle.
2. Voracious Hunters: Dragonflies are among the most efficient hunters in the insect world, with a hunting success rate of 90% to 97% when capturing prey.
3. Vanquishers of Mosquitoes: Adult dragonflies can consume hundreds of mosquitoes daily, significantly impacting mosquito populations. Their larvae (nymphs) also prey on mosquito larvae in aquatic environments.
4. Monster Appetites: In their nymph stage, dragonflies can eat an average of 40 mosquito larvae per day, reducing the larval population by approximately 45% in controlled environments.
5. Acrobatic Fliers: Dragonflies can fly at speeds of up to 35 miles per hour (56 km/h), making them one of the fastest flying insects.
6. Unique Flight Mechanics: They possess two pairs of wings that can move independently, allowing for exceptional maneuverability, including hovering, flying backward, and making sharp turns.
7. Versatile Hunters: Dragonflies use two primary hunting strategies—patrolling, where they fly along specific routes, and hawking, where they perch and wait to ambush prey.
8. Calculating Predators: When chasing prey, dragonflies can calculate the trajectory of their target and adjust their flight path accordingly, ensuring a high likelihood of interception.
9. Lifespan Variability: While adult dragonflies typically live for a few weeks to a few months, their nymphs can survive underwater for up to five years, depending on the species and environmental conditions.
10. Testy About territory: Many male dragonflies are territorial and will defend their hunting grounds aggressively against rivals, often engaging in aerial displays to assert dominance.
11. Diverse Diets: Besides mosquitoes, dragonflies feed on various insects, including flies, moths, and even smaller dragonflies, showcasing their adaptability as predators.
12. Ecosystem Indicators: The presence of dragonflies is often an indicator of a healthy ecosystem since they require clean water bodies for breeding and hunting.
13. Cultural Significance: In many cultures around the world, dragonflies symbolize change and transformation due to their remarkable life cycle from nymphs to adults.
14. Environmental Benefits: By controlling mosquito populations, dragonflies play a crucial role in reducing the spread of mosquito-borne diseases such as malaria and dengue fever.
15. Unique Mating Rituals: Dragonfly mating involves unique aerial displays where males will often grasp females by the neck while flying in tandem—a formation known as a "heart" shape during copulation.

There are more than 130 documented species of dragonfly in Hong Kong. Two of these species are endemic to our little city, meaning they can’t be found anywhere else in the world!

For a full list of Hong Kong dragonfly species, check out the document below:

Notable Dragonfly Species in Hong Kong

These are the the Fukienogomphus choifongae and Leptogomphus hongkongensis. You can find photos pf both species here.

In addition to our two endemic species, there are also a couple of dragonflies in Hong Kong that are unique on a novel level. Firstly, we have the Nannophya pygmaea or Scarlet Dwarf Dragonfly – the smallest dragonfly species in the world! Adults measure in at just 1.5 cm long with a wingspan of about 2 cm.

If you wish to see this incredible species, you can try your luck in far-flung areas of Hong Kong like Kau Sai Chau, Pat Sin Leng, Yung Shu O, Cheung Sheung, Tai Tong and Tin Fu Tsai.

The second novel species in Hong Kong is the Agriocnemis pygmaea, otherwise known as the Pygmy Dartlet, Wandering Midget or Wandering Wisp (which is my favorite of the three names). This species is technically classified as a damselfly, with adults reaching a maximum body length of 1.9 cm and with the wings measuring in at 1.1 cm.

You can find this species in the Hong Kong Wetland Park!

For a full list of dragonflies in Hong Kong provided by the Agricultural Fisheries and Conservation Department, check out the excel file below.

Dragonflies of Hong Kong List

Dragonflies and damselflies, both belonging to the order Odonata, exhibit several key differences that distinguish them from one another. Here are the main distinctions:

Size and Body Structure

• Dragonflies are generally larger and have thicker bodies compared to damselflies. Their bodies typically exceed 2 inches in length, while damselflies are usually between 1.5 to 2 inches long and have a more slender, delicate appearance.

Eyes

• Dragonflies possess larger eyes that often touch or nearly meet at the top of their heads, providing them with a wide field of vision. In contrast, damselflies have smaller eyes that are separated by a noticeable gap.

Wings

• When at rest, dragonflies spread their wings perpendicular to their bodies, while damselflies typically fold their wings back along their bodies. Additionally, dragonfly wings are usually broader at the base compared to the more slender wings of damselflies.

Flight Behavior

• Dragonflies are known for their strong and agile flight, capable of rapid movements and hovering. They often exhibit a direct and fast flight pattern. Conversely, damselflies tend to flutter and float more gracefully through the air.

Taxonomy

• Dragonflies belong to the suborder Anisoptera, which means "different wing," indicating the varying shapes of their forewings and hindwings. Damselflies fall under the suborder Zygoptera, meaning "same wing," as their forewings and hindwings are similar in shape.

Dragonflies require fresh water to complete their growth cycle. After females lay eggs near suitable bodies of water, the larvae can spend up to five years growing. Dragonfly nymphs are voracious predators, feeding on a variety of aquatic organisms, including mosquito larvae, small fish, and other invertebrates. When ready, they go through an “emergence” where the larvae shed their exoskeletons and become dragonflies!

Because a dragonfly’s lifecycle is so reliant on freshwater habitats, you can easily spot dragonflies in public parks with water features or while hiking. Seek out the following types of habitat for a higher chance of spotting dragonflies in the wild:

1. Freshwater Ponds: Dragonflies are commonly found in freshwater ponds, where they lay their eggs and hunt for insects. These ponds provide a rich habitat for both adult dragonflies and their aquatic nymphs.
2. Streams and Rivers: Sandy and rocky streams, such as the Tung Chung River, are ideal locations for dragonflies. This river is one of the few large natural rivers remaining in Hong Kong and hosts a variety of dragonfly species. The recent discovery of the Asiatic blood tail (Lathrecista asiatica) near this river highlights its ecological significance.
3. Marshes and Wetlands: Seasonal marshes and wetlands are critical habitats for dragonflies, offering abundant food sources and breeding grounds. These areas are essential for maintaining biodiversity, as they support various dragonfly species, including the Hong Kong Clubtail (Leptogomphus hongkongensis), which prefers muddy gravel areas in small wooded streams.
4. Reservoirs: Dragonflies can also be found around reservoirs, where they benefit from the still waters that provide perfect conditions for laying eggs. The surrounding vegetation offers perching spots for adults to scout for prey.
5. Mangroves: Certain species, such as the Mangrove Skimmer (Orthetrum poecilops), inhabit mangrove ecosystems, particularly in areas like Tung Chung and Tai O on Lantau Island. These unique habitats support dragonflies that have adapted to brackish water conditions.
6. Waterfalls: Dragonflies are often spotted near waterfalls, where the combination of flowing water and surrounding vegetation creates an ideal environment for hunting and reproduction.