Of dragonflies…
“I love to see the sunshine on the wings of the Dragonflies… there is magic in it.” Ama H.Vanniarachchy
One of my favourite cartoons of all time is “The Rescuers”. The characters are simply fabulous – and Evinrude is no exception. Now “Evinrude Outboard Motors” was a North American company that built a major brand of two-stroke outboard motors for boats – and when you watch the clips in the info box, you will see where Evinrude got his name! Seriously, take the time to watch the clip – it is quite delightful! What, you may well ask, is Evinrude? Well – he’s a Dragonfly!!
Odonata is an order of flying insects that includes the dragonflies and damselflies. Around 6500 species (numbers vary according to source) are alive today, and they go back roughly 300 million years. According to the IUCN, “only a fifth of the nine million species of animal, plant and fungus thought to occur on earth are known. (The Odonata species) are generally considered well-known, but researchers have recently described 60 new species in Africa, the greatest number of newly described Odonota in about a century.”
Dragonflies are not Damselflies… Whilst the two suborders are often just called dragonflies, there are important differences that make damselflies distinct. Perhaps the most obvious difference is the way their wings lay when at rest. A dragonfly’s wings are spread out flat like an airplane when it is at rest, while a damselfly will fold its wings over its back. Other differences include the body shape (dragonflies have thicker bodies than the slender damselflies) and their eyes (damselflies have two distinct eyes while the eyes of dragonflies typically almost meet in the middle of their head). Aside: Google “damselfly eyes” for an interesting look at the difference.
Dragonflies, like all insects are cold-blooded / exothermic or ectothermic (the preferred term these days). The term ectotherm comes from the Greek “ektos”, meaning outside, and “thermos”, which means heat. As such, they must have sunlight to warm their bodies before they begin their day. On cloudier days, you may not see active dragonflies, whilst on a hot summer’s day, one can often find dragonflies flitting about a water source. The reality is that dragonflies need sunny warm weather to fly, and the temperature must be over about 20°C. If it is too cold, or even wet, they hide in the foliage. On colder days, dragonflies do something similar to shivering when they’re to cold to fly. This is called “wing-whirring” and consists of them vibrating their wings – presumably to warm up their wing muscles just enough to fly. See video in the info block.
Dragonflies have a rest state called “torpor,” which is similar to sleeping. During this state, their body cools down and they’re unable to fly around. During torpor, they are slow to respond to stimuli. It can take more time to react to danger, which can lead to their deaths if they’re not careful. They keep themselves safe by hiding in the vegetation, behind reeds, or even just clinging onto the undersides of leaves when they “sleep”. In general, dragonflies sleep at night, when the temperatures are lower, and it is harder for them to hunt. You can often see dragonflies that are slow and sluggish early in the morning or late in the evening.
On the opposite side of the scale, if they get too hot, different chemical reactions start taking place in their bodies that can result in death if they become severely overheated. Dragonflies use the “obelisk” (a tapering stone pillar) position to reduce their body temperature (see images above and below). By extending their abdomens upwards, they minimize the amount of sun hitting their bodies. If the obelisk position isn’t enough to cool the insect down, he’ll fly into a cool, shaded area – even if it means abandoning his territory for a while (because defending a territory isn’t worth risking death by overheating). They may occasionally also lower their abdomen, allowing it to hang down as they fly, to reduce body temperature.
Odonata are considered to be good bioindicators of environmental health and water quality – because all the species within this order are dependent on water for the development of their pre-adult stages (commonly known as nymphs, naiads or larvae). It obviously follows that water pollution has a negative impact on dragonflies due to their reliance on aquatic ecosystems throughout their life.
After mating the female dragonfly lays her eggs in or near the water (species dependent). The eggs take one to five weeks to hatch, and then the larvae (called nymphs) can live underwater for as long as two years. This is considered to be the longest stage in the life cycle of a dragonfly. Eventually an appropriate spot is found, and the nymph slowly pushes out of their shell body to emerge as an adult dragonfly. See the video in the info box.
Dragonflies are incredible flyers. They often hunt other flying insects, and so agility is key. To facilitate this, they can move and rotate each of their four wings independently. This enables these insects to fly backwards, up and down, turn on a dime and even hover. According to the Smithsonian, they are the fastest flying insects – with speeds of up to 56 km/h! When flying in a straight line, dragonflies can accelerate with up to 4 g of force. When they turn corners, this increases to 9 g!! Most humans would pass out with G forces of just four or five…
There are just so many more fascinating facts about these insects… In one study, dragonflies were observed to have up to a 95% success rate in capturing prey. For comparison, lions have about a 25% success rate. Some of them migrate – the individual globe skimmer (Pantala flavescens) flies more than 6,000 km! One could go on and on…
I hope we’ve piqued your interest enough to appreciate these phenomenal little creatures when next you see them in your garden!!
Jacqui Ikin & The Cross Country Team
INFO BOX:
The Rescuers – Evinrude:
Dragonfly Wing Whirring:
Dragonfly emerging:
An awesome field guide if you’re interested:
