Reproduction in dragonflies and damselflies
How dragonflies and damselflies reproduce is unique in the animal kingdom. The male has two separate sets of reproductive organs: one is for sperm production and the other for insemination of the female; there is no connection between the two.
The male dragonfly produces sperm near the tip of the abdomen, in segment 9. Before fertilisation the male must transfer sperm to a set of Secondary Genitalia situated at the opposite end of the abdomen, closer to the head, between segment 2 and 3.
Because of this, reproduction is not performed with abdomens ‘tip to tip’ as with other insects, and the female must connect her tenth segment to the male’s second segment to fertilise her eggs, aligning themselves in a so called ‘wheel’ posture.
Copulation
The male abdomen has special Anal Appendages at the tip, used as claspers to capture and hold the female in the ‘Tandem’ posture. In dragonflies, the female is held by the head. Damselfly females are held by the Pronotum, a shield-like plate located just behind the head. The shape of the claspers and pronotum are unique to each species, helping avoid interspecies hybridisation.
With the female held by his claspers, the male flexes his abdomen underneath him, bringing the tip to segment 2 for the transfer of sperm to his secondary genitalia. The male straightens his abdomen again to allow the female to manoeuvre into the wheel posture. This facilitates the connection the female segment 10 to the male segment 2, fertilising the eggs with sperm.
Dragonflies and damselflies may often be seen in tandem and wheel postures (‘in cop’), either at rest or flying. Some species like the Blue-tailed Damselfly – Ischnura elegans may remain coupled this way for several hours, but in species such as Broad-bodied Chaser – Libellula depressa copulation lasts only seconds and is done on the wing.
Egg laying – Ovipositing
Damselflies usually remain in tandem or with the male close by, while the female lays, or Oviposits, her eggs. In some dragonfly species such as hawkers, the female lays her eggs completely alone, but others remain in tandem similar to damselflies. There is no internal gestation period and fertilised eggs are oviposited immediately following copulation. Eggs are laid in or close to water, and the female may oviposit hundreds or thousands of eggs after successful breeding.
There are two distinct methods used by dragonflies and damselflies while ovipositing, each species relies on one method.
Exophytic ovipositors
Species that deposit their eggs in water are known as Exophytic ovipositors, the eggs sink to the bottom to eventually hatch in the sediments below. Darter and Chaser species do this in flight, and dip their abdomen into the water repeatedly, releasing eggs each time. In some species the female does this alone, but others stay in tandem. In tandem ovipositing the pair fly close over the water’s surface together. With remarkable control and synchronised precision, the male ‘flicks’ the female, dipping the tip of her abdomen below the water as she releases her eggs.
Endophytic ovipositors
Some species inject their eggs directly into submerged plants or other substrates like mud or rotting wood. These are Endophytic ovipositors, and include Hawker dragonflies and all damselflies. Emergent bankside plant and reed stems above the water line may also be used. Species like the Willow Emerald – Chalcolestes viridis oviposit into the bark of tree branches that overhang water, and the resultant larvae drop in to the water below when they hatch.
Some damselflies may completely submerge underwater for minutes at a time to find the most suitable location to lay their eggs. The male remains in tandem with the female and will assist in breaking free of the water’s surface tension to take to the air again.
Eggs hatch usually after a few weeks, but in some species they will hatch the following spring.
