Despite being just 4.5cm long, banded demoiselles and beautiful demoiselles are Britain’s largest damselflies. Often mistaken for their dragonfly relatives, these insects form their own group within the order Odonata. Easy ways to spot the difference are their slender bodies and slow, gentle, fluttery flight. Damselflies also fold their wings vertically when resting, while dragonflies hold theirs out to the side. 

Another wing-related clue is that, for damselflies, both pairs are roughly the same size and shape. Dragonflies, by contrast, tend to have hindwings (nearer the tail) that are broader and shorter than their forewings (nearer the head). This is reflected in the names of their sub-orders: Zygoptera (damselflies) means "even/paired wings", while Anisoptera (dragonflies) means "uneven/unequal wings".

If you can get a closer look, you might see another key distinction. Both dragonflies and damselflies have short antennae, and so rely on their sight to navigate and find food. Their eyes have a compound structure comprised of many tiny lenses, which gives them a very wide view of their surroundings. But while dragonfly eyes often meet in the middle, damselflies have eyes on the sides of their heads.

Pictured below from left to right (click to expand): Male banded demoiselle / Female banded demoiselle / Male and female beautiful demoiselles.

Like many wildlife species, demoiselles are sexually dimorphic, which means that the sexes are visually distinguishable from each other. The males are inky blue with a turquoise sheen (both species), while the females are metallic green (banded) or greenish-bronze (beautiful). Due to these similarities, the two species look very alike at first glance, but luckily they can be identified by their unique wing colours.

The wings of the males are dark all over (beautiful) or have a dark "fingerprint" patch across the middle (banded). In females, the difference is more subtle and can be trickier to notice against background vegetation: their wings are brown (beautiful) or pale green (banded), with a faint white spot at the tip. In fact, demoiselles are the only British damselflies whose wings have colour!

Pictured below from left to right (click to expand): Female beautiful demoiselle laying eggs / Demoiselle larva.

Demoiselles start their lives as eggs, which the females inject into the stems of plants like water crowfoot – they may even go below the surface to find a good spot. Two weeks later, the young hatch as larvae; a life stage that lasts for two years. They spend this time among submerged plants, eating smaller invertebrates and hiding from predators. In the higher flows of winter, they may hunker down in mud, silt, and gravel on the stream bed.

When they are fully grown, the larvae climb up "emergent" plants - these are ones that root in the water but extend above the surface. Once in the fresh air, the larvae shed their exoskeletons and take to the sky on their newly unfurled wings. In flight, both species are fierce predators that catch other insects with their six bristly legs. You might also see them basking in the morning sun, or sheltering in vegetation as night falls or wet weather arrives.

For the most part, though, demoiselle adulthood is about reproduction. The males take and defend small territories, performing aerial dances to attract passing females. If the wooing goes well, each pair forms a “wheel” or “heart” shape for mating, and he leads her to a good egg-laying site. Look out for this amazing spectacle between April and October, but especially on bright, dry, windless days between May and August.

The lush plant life of our chalk streams makes them great habitats for both demoiselle species. Of the two, the beautiful demoiselle is more sensitive and in particular need of the gravelly bed, consistent temperature, and clean, oxygen-rich water that our chalk streams provide.

This means that if we want to give these incredible insects a home, we need to keep our chalk streams healthy by tackling pollution and agricultural runoff, reducing water abstraction, creating a balance of light and shade, and letting vegetation flourish along the riverbanks.

If you’d like to learn more about chalk stream wildlife, and how we're working to protect chalk streams, check out the Watercress and Winterbournes scheme - there are lots of ways to explore and get involved!

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