The Garden is abuzz at the moment, teeming with insects of every colour and shape – butterflies, moths, bumblebees, solitary bees, caterpillars, grasshoppers and crickets to name but a few. But, among the biggest and most impressive of all are the dragonflies, zooming around at high speeds!
Dragonflies can be recognised by their large bodies and two narrow pairs of wings with complicated patterns. Dragonflies are similar to damselflies and both belong to the same order of insects, Odonata. Here are a few key differences between these two groups:
- Damselflies are smaller than dragonflies.
- Dragonflies rest with their wings open, while damselflies rest with their wings closed.
- The eyes of a dragonfly meet at the top of the head, while the eyes of a damselfly do not touch.
However, these characteristics may be hard to distinguish from afar especially when they’re moving very fast. The simplest way to tell apart dragonflies and damselflies is while they’re in flight – dragonflies are far more robust, their flight is strong and purposeful and they often fight with each other in the sky. Damselflies on the other hand are much smaller and more delicate, with a weak and fluttering flight. Both groups of insects are amazing to see and can be found in a variety of wetland habitats, especially those with good water quality.
Dragonflies are remarkable creatures, being some of the first winged insects to evolve more than 300 million years ago – they pre-date the dinosaurs by nearly 100 million years!
A few clues to the ancient lineage of dragonflies can still be observed today: they have very complicated and intricate patterns on their wings, that isn’t seen in later insects which have very few veins in their wings. In addition, the wing muscles of dragonflies are connected directly to their wings, allowing them to move each wing independently, which enables a spectacular display of aerobatics! This is also why dragonflies make such a noise when they fly past, as they have a much slower wing beat of 30-40 beats per second, compared to midges that beat their wings at 1,000 beats per second.
Another incredible feature of dragonflies is their vision. They have huge compound eyes, comprised of 30,000 individual facets – the largest eye to body size ratio of all animals. Dragonflies can even see faster than we do; whereas humans see 60 images per second, dragonflies see around 200 images per second. This allows them to see, react to and capture other insects mid-flight, which requires 80% of the brain to process this visual information!
The dragonfly lifecycle is also very interesting, with an aquatic larval stage that can last more than five years. The males of some species are highly territorial and engage in constant battle to defend suitable breeding sites. Males and females come to together to mate in a ‘wheel’ position, and can often be seen flying around like this. The females then lay fertilised eggs in submerged vegetation or directly into the water. The following spring, the eggs will hatch and the larvae will emerge – dragonflies spend most of their lives as nymphs underwater, feeding on other insect larvae, tadpoles and even small fish. During their time underwater, the larvae undergo 5-14 moults before they’re ready to crawl out of the water and shed their skin one last time to complete their metamorphosis into adulthood. Larval development typically takes one or two years, however this depends on the species, water temperature and the amount of available food.
When the nymph is fully grown, it climbs up out of the water to find a suitable place to emerge. They redistribute their body fluids so that the skin on the back splits open and the adult dragonfly slowly emerges, leaving behind the empty skin, called the exuvia. It takes a while for the wings and body to expand and harden so, at this point, they are very vulnerable; it has been estimated that up to half of emergences are unsuccessful due to predation. Newly-emerged dragonflies are immature (called ‘tenerals’); they are thinner, paler and weaker in flight and it takes a few weeks of feeding and good weather before they are fully mature and ready to search for a mate.
Dragonflies are truly amazing insects with fascinating life histories. Keep a look out for some of the species that we have here at the Botanic Garden:
- Emperor Dragonfly (Anax imperator)
- Southern Hawker (Aeshna cyanea)
- Common Hawker (Aeshna juncea)
- Migrant Hawker (Aeshna mixta)
- Common Darter (Sympetrum striolatum)
- Black-tailed Skimmer (Orthetrum cancellatum)
- Broad-bodied Chaser (Libellula depressa)
- Four-spotted Chaser (Libellula quadrimaculata)
- Golden-ringed Dragonfly (Cordulegaster boltonii)
References:
British Dragonfly Society https://british-dragonflies.org.uk/odonata/life-cycle-and-biology/#:~:text=Mating%20in%20dragonflies%20is%20unique,abdominal%20claspers%20(tandem%20position).
BBC Earth https://www.bbc.com/reel/video/p035dt53/dragonflies-see-the-world-in-slow-motion
WWT https://www.wwt.org.uk/discover-wetlands/wetland-wildlife/dragonflies-and-damselflies/