The beautiful demoiselle (Calopteryx virgo) is a species of damselfly belonging to the family Calopterygidae.

In the final stage (F-0-stage), larvae are 3.5–4.6 millimetres long and weigh about 4 milligrams, slightly smaller than those of the banded demoiselle.

[6] These large, dark damselflies have small, lateral, hemispherical eyes; two pairs of wings similar in shape; and a slender abdomen.

The wings have a dense internal network of veins, and can be transparent or uniformly colored at their basal area.

[6] This species is similar to the banded demoiselle (Calopteryx splendens), another British damselfly with coloured wings.

[7] Beautiful demoiselle are distributed across all of Europe with the exception of the southwestern Iberian Peninsula, the Balearic Islands, and Iceland.

Regular findings come from areas up to a maximum height of 980 m above sea level; occasionally, they may be found up to 1,200 meters in altitude, such as in the Alps.

In the northern part of their range, such as in Norway and Finland, they are also found near medium-sized rivers or even larger streams.

Because of this, it is extremely rare to find them in barren locations, flat expiring banks, or areas with a smooth stone floor.

This species prefers cooler, shadier areas of the water, with an optimal summer average temperature between 13 and 18 °C.

They prefer cool, shady waterways, with a more or less strong current, and near-natural vegetation and bank structure.

Due to their broad wings, the beautiful demoiselle can be blown away by the wind more easily than other species of damselflies.

They are characterized by an increased flow and a suitable oviposition substrate in the potential breeding sites.

The size of the territories and their distance apart is dependent on the population density as well as availability of suitable habitat.

Females will fly over the water in search of suitable nesting places, passing through the territories of males along the way.

The eggs are laid in the stems of aquatic plants at or below the water level, where the female can submerge for up to 90 minutes.

In the Middle East, the larval development of the beautiful demoiselle usually takes 6–8 weeks, mainly due to the preference for cooler waters.

This includes the larvae of black flies, midges, stoneflies, and mayflies, and they may also feed on amphipods.

This differs from the banded damselfly, who have thin-skinned tracheogenic appendages which make them less sensitive fluctuations in oxygen supply.

Males will stay in sunlit areas throughout the day, typically reaching the water in the early morning.

In shaded environments, the damselflies will arrive later, and are usually seen basking on the top of surrounding vegetation.

Females fly over the waters throughout the day in search of suitable nesting sites, and both sexes will engage in hunting, advertising, mating and egg laying during the warm midday hours.

Male beautiful damselflies do not range far from their breeding, hunting, and resting areas, only going a relatively small 20–100 metres (66–328 ft).

It is completely absent in major cities and industrial centers, and even in regions with strongly pronounced agricultural use it is found only rarely.

Because of this, the Red Data Book (1998) of Germany classifies it as endangered in some states, even in danger of extinction.

In addition, the larvae have less to hold onto the current, and the algae and dirt particles settle into their gills restricting respiration.

Fast growing plants, such as meadowsweet (Filipendula ulmaria), the stinging nettle (Urtica dioica) or Himalayan balsam (Impatiens glandulifera), may cause the area to become overgrown.

Additionally if tree growth on the waters edge results in a closed canopy, the damselflies will lack the necessary sunlight.