Dragonflies and damselflies: nature’s mercurial insects

A kind of aerodynamic, multicoloured “helicopter” suddenly appears, slender and elegantly inquisitive, with two panoramic eyes, four wings, a wide thorax, and a cylindrical body that draws our attention to the adventure of life in aquatic habitats. Come get to know the Odonata.

On a mild, sunny afternoon, instincts idle and rest quietly at the edge of a lake with translucent, spring-like water. Now you can sit back and relax, away from the hustle and bustle of everyday city life. But just when we think that nothing and no one can upset this balance, a kind of aerodynamic, multicoloured “helicopter” suddenly appears, slender and elegantly inquisitive.

With two panoramic eyes, four wings, a wide thorax, and a cylindrical body, this creature draws our attention to the adventure of life in these humid habitats.

This fascinating insect, which “paints” patterns of unpredictable colours in the air, is our new BIOgallery guest: the dragonfly or damselfly (often confused with one another). The term “damselfly” is more commonly used for smaller, more delicate species, while “dragonfly” refers to larger species. Both instantly transport us to the heart of the biodiversity found in lakes, rivers, and other highly humid natural habitats.

In Portugal, there are around 65 species of dragonflies and damselflies, all belonging to the Odonata order, with names as simple as they are amusing. For example, the blue emperor (Anax imperator), the lesser emperor (Anax parthenope), the vagrant emperor (Anax Ephippiger), the blue hawker (Aeshna Cyanae), the migrant hawker (Aeshna mixta), the common darter (Sympetrum striolatum) or even the red-veined darter (Sympetrum fonscolombii).

Love is in the air

Curiously, dragonflies approach reproduction with a certain flair of performance art. When the female selects a male, they begin a nuptial flight dance. They immediately join together in the shape of a heart, with the male transferring sperm to the area under the abdomen known as the secondary genitalia. The tip of the abdomen has claspers, which the male uses to grasp the female’s head.

Procreation occurs when the female bends the tip of her abdomen to make contact with the male’s secondary genitalia. It is in this poetic and athletic manner that dragonflies mate, capable of doing so in flight for a few minutes or even several hours.

Long before love messages were flown by aeroplanes over our beaches, dragonflies had perfected the art of grand declarations in the sky.

Some species, such as the red-veined darter (Sympetrum fonscolombii) even lay their eggs during mating and wait between two and three months before hatching. Generally, all dragonflies lay their eggs in natural or artificial aquatic habitats, such as lakes, rivers, ponds, or even small garden ponds.

When they hatch, dragonfly larvae are voracious, with a predatory hunger that knows no bounds, feeding on the larvae of other insects, invertebrates, frogs, and even fish.

They are instinctively precocious and highly physical. The body of the offspring resembles that of the adult, being divided into three parts and with three pairs of legs. The vast majority leave their comfort zone at around three months old, but species such as the golden-ringed dragonfly (Cordulegaster boltonii) take to the air only after a year of juvenile development.

But before they can dream of taking to the skies, they must first shed their exoskeleton — a flexible yet resilient layer — that supports them and allows initial growth without reaching the adult stage. When the last layer of the exoskeleton is shed, the wings finally have space to emerge in triumph. That is when the true adventure in the air begins.

3, 2, 1, takeoff…

Some species, such as the red-veined darter (Sympetrum fonscolombii) even lay their eggs during mating and wait between two and three months before hatching. Generally, all dragonflies lay their eggs in natural or artificial aquatic habitats, such as lakes, rivers, ponds, or even small garden ponds.

When they hatch, dragonfly larvae are voracious, with a predatory hunger that knows no bounds, feeding on the larvae of other insects, invertebrates, frogs, and even fish.

This is one of the most important moments in the lives of these colourful insects. What was once a watery, idyllic, and comforting space becomes a veritable killing field, where the need for survival prevails above all else. Rivers, lakes and ponds can easily drown dragonflies if their first flight goes badly.

Nature rarely gives wings to empathy and almost never grants second chances. It is at this point that the dragonflies’ new membranes are really put to the test.

It’s all or nothing. With their eyes on the sky and instincts sharpened, they begin to beat their wings and find comfort in the unknown, gaining confidence and a sense of the future as they venture towards the blue horizon. The start is quick, the test a real success and they fly off into adulthood.

No safe haven

Unfortunately, with the advance of climate change and, above all, the impact of human development, it is becoming increasingly difficult for these beautiful insects to find a safe haven in which to land and rest their wings. To survive, they need freshwater, the quality of which has been declining, largely due to widespread pollution and poor management of water resources.

An example of this is the intensive extraction of water for agricultural purposes in the Mediterranean region, which has contributed to the disappearance of many habitats essential to the survival of this species. The indiscriminate cutting down of vegetation and the growth of tourism have also contributed to the substantial decrease in its natural spaces. Proof of this is the fact that these species are most threatened precisely in the most developed regions, such as Europe.

Currently, more than 50% of Odonata species are endangered, especially in Europe, where data shows that 46% are threatened with extinction and a further 21% are near threatened.

There is yet another problem, resulting from the excessive fertilisation of waters due to human activity. The high concentration of nutrients in areas of intensive agricultural activity promotes the proliferation of bacteria and decomposer algae, which consume much of the oxygen in the water, thus compromising the subsistence of dragonflies.

It is these situations that have led to a 29% decline in dragonfly and damselfly populations across Europe.

A mercurial planet

A recent study recently revealed that dragonfly larvae are the most ingenious and straightforward way to detect areas with high levels of mercury.

Over the years, fish and birds have been observed and analysed to detect the spread of this metal. However, because dragonfly larvae thrive in a wide range of wetlands, from water-rich areas to swamps and even desert areas, these insect offspring have risen to the top of evaluation rankings and are regarded as a standard of excellence in mercury detection.

This research is led by the “Dragonfly Mercury Project”, a project of scientists and ecologists studying the spread of mercury around the planet. The interest generated by this group has been overwhelming and impactful across multiple locations, bringing together all kinds of communities in search of dragonfly larvae.

Mercury is a toxic metal that is harmful to much of the animal life on planet Earth. Industrialisation has increased its presence in the atmosphere and turned it into one of the most dangerous chemicals for public health.

Due to the bioaccumulation inherent to the food chain, it can travel from insects to birds, from birds to fish, and from fish to humans. This is especially true for those who consume large fish, such as sharks or swordfish, in which the presence of this metal is particularly pronounced.

The human body is unable to break down mercury into a less toxic form, and the chemical is simply stored, potentially causing serious neurological and general health problems.

Did you know that…

• Dragonflies are the terror of mosquitoes and unsung heroes of the human population. It is estimated that they can eat up to 100 mosquitoes a day.
• The world’s smallest dragonfly, the “scarlet dwarf” (Nannophya pygmaea), is found mainly in Southeast Asia, in China and Japan. It is only 15 mm long.
• They have powerful mandibles. This fact is reflected in the name Odonata. This term comes from the Greek “odon” which translates to “tooth”. As they hunt in mid-air, dragonflies rely on efficient, lethal mandibles to ensure the immediate subduing of their prey.
• The prehistoric ancestors of dragonflies and damselflies were of frightening proportions, with wings spanning up to a metre in length (the Meganeuropsis permiana being the record holder). Such growth was possible because these insects possess a tracheal respiratory system and an open circulatory system, which limits their size according to the atmospheric concentration of oxygen. During the Palaeozoic Era, it is estimated that oxygen levels were so high that these species were able to grow to enormous sizes.