Having spent two years as aquatic larvae, or nymphs, banded demoiselles live only a few weeks as winged adults. Reproduction is now their top priority. During mating, the male uses claspers at the tip of his abdomen to grasp the female behind her head tightly enough to resist the attempts by other males to dislodge him – they are now said to be ‘in tandem’.
If the pair manage to avoid any interlopers and settle, the male flexes his abdomen to encourage the female to loop her abdomen round to interlock with him, forming the ‘wheel’ position. The male removes any sperm that the female has already received, then inserts his own.
Mating lasts less than five minutes in banded demoiselles, though can take longer in other damselfly and dragonfly species. Afterwards the pair separate, but the male guards the female from rivals while she lays her eggs. The female pushes these into plants in the water, so searching for patches of emergent vegetation in slow-flowing waterways is often the best way to spot this fascinating behaviour.
7 KEY SIGNS YOU NEED TO LOOK OUT FOR
1. Display colours Male demoiselles are territorial and display to the bronzy-green females by flicking their wings open to show off the bright blue patches – both when perched and also in flight, seeming to flutter like a butterfly.
2. Strong thorax This section between the damselfly’s head and abdomen houses the massive muscles that power its wings. The thorax is a very robust, rigid structure with internal bracing to withstand the forces exerted by the muscles.
3. Compound eyes Damselflies and dragonflies have large compound eyes with many facets. This provides enough resolution to detect and capture insect prey in flight. Damselfly eyes are separated on either side of the head; those of the larger dragonflies join in the centre.
4. Spiny legs The legs of banded demoiselles are covered in long spines. This is an adaptation to help catch prey – a demoiselle positions its legs in front of its head, forming an efficient ‘net’ to scoop up insects in midair.
5. Male claspers The twin claspers at the end of the male’s abdomen fit the female’s pronotum, a shield covering the front part of the thorax. They are strong enough to keep a pair firmly coupled during flight.
6. Two pairs of wings All members of the Odonata – that is, damselflies and dragonflies – have four wings. The two pairs move independently, giving great agility – the insects can hover and even fly backwards.
7. Sperm-transfer organs The male has secondary genitalia under the second and third segment of his abdomen. With the female in the tandem position, he transfers sperm here from his sperm-storage reservoir. She receives the sperm when they are in the ‘wheel’ position.
MORE BANDED DEMOISELLE BEHAVIOUR TO SEE
AGGRESSION Pairs are mobbed by solo males trying to displace their coupled rival. They can even be driven into the water.
LAYING Females insert their eggs in aquatic vegetation, which hatch in about 10 days. The larvae emerge as adults after 18 or so moults.
SUBMERGENCE Females often submerge entirely to find suitable egg-laying sites – they may rely on trapped air bubbles to breathe.