Sussex Dragonfly Group

Downy Emerald
Cordulia aenea (Linnaeus, 1758)
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Suborder: Anisoptera
Family: Corduliidae

Downy Emerald
Cordulia aenea

Suborder: Anisoptera
Family: Corduliidae

The two Emerald Dragonfly species can be found at the same site, patrolling fairly sheltered heathland ponds or hawking high in the woodland canopy, rarely settling. As a result, distinguishing between them can be a frustrating task. The Downy Emerald usually goes for the more open areas, flying very low, regularly turning back and forth, and hovering. It appears shiny black in flight, except for the transparent wings. Both sexes have a bronze-green downy thorax and a dark metallic green abdomen, which is club-shaped in the male and rounded in the female. Young newly breeding adults have beautiful greenish yellow eyes and bronzey abdomens going duller with age. The female lacks the conspicuous ovipositor (vulvar scale) of Somatochlora metallica.

Cordulia aenea
1 / 7
teneral male
Photo: David Sadler
Cordulia aenea
2 / 7
female
Photo: David Sadler
Cordulia aenea
3 / 7
female
Photo: David Sadler
Cordulia aenea
4 / 7
male
Photo: David Sadler
Cordulia aenea
5 / 7
male
Photo: David Sadler
Cordulia aenea
6 / 7
male
Photo: David Sadler
Cordulia aenea
7 / 7
mating
Photo: David Sadler

More images

National status
A nationally rare species, and listed in the British Red Data Book on Invertebrates. With a stronghold in south-east England, it has an otherwise scattered distribution from Devon to the Scottish Highlands.

Status in Sussex
Thinly but widely and inconsistently scattered across the county including the south east from where the 1965-1978 survey had no breeding records (Chelmick 1979). Listed in the Sussex Rare Species Inventory.

Distribution at 1km scale

Cordulia aenea distribution (all)
Cordulia aenea distribution pre 1980
Cordulia aenea distribution 1980 - 1989
Cordulia aenea distribution 1990 - 1999
Cordulia aenea distribution 2000 - 2009
Cordulia aenea distribution 2010 - 2019
Cordulia aenea distribution 2010 on

Historical records
All authorities (e.g. Lucas and Bloomfield 1905; Craven 1922) seem to agree that the first record for Sussex is by Unwin who found one near Horsham in June 1846. However, up until 1945 there had been only three localities recorded in West Sussex (Dannreuther 1945), and it seems to have fared only slightly better in East Sussex (Chelmick 1979). In the north and west of the county Chelmick (1979) considered it widespread and common.

Flight times
Early May - late July. The flight time appears to have moved forward slightly during the decade to 2020.

Phenology (adult)

Cordulia aenea phenology (all)
Cordulia aenea phenology pre 1980
Cordulia aenea phenology 1980 - 1989
Cordulia aenea phenology 1990 - 1999
Cordulia aenea phenology 2000 - 2009
Cordulia aenea phenology 2010 - 2019
Cordulia aenea phenology 2010 on
Cordulia aenea habitat
1 / 1
Downy Emerald habitat near Lavender Platt, Ashdown Forest
Photo: Simon Linington

Habitat
Preference for nutrient-poor, acidic, tree-lined or woodland (usually deciduous) ponds, lakes and canals. Occasionally, slow-flowing rivers and streams, with trees and overhanging branches.

Conservation
Since the larvae live in the slowly decomposing vegetation at the bottom of (usually still-water) body, dredging could pose a serious threat. A further threat comes from nutrient enrichment of water caused by run-off from adjacent cultivated land or fertilised pasture. Loss of woodland ponds or clearance of their tree-lined fringes poses problems for the adults.

Similar species
This species is only likely to be confused with the Brilliant Emerald in Sussex. Ultimately, identification boils down to the amount of yellow on the upper face (frons), the shape of the tail / anal appendages and in females, the presence or absence of a ‘vulvar scale’ that protrudes at right angles below the tip of the abdomen. Appearance in flight, flight times and behaviour are also pointers but not infallible.

The Downy Emerald lacks the extensive yellow on the frons of the Brilliant Emerald. The anal appendages of the male Downy Emerald are blunt and outward-pointing whereas those of the Brilliant Emerald are pointed and inward-pointing. The appendages of the female Downy Emerald are shorter than those of the Brilliant Emerald though being a relative difference this is of limited value. Thankfully, the Brilliant Emerald has a distinct vulvar scale below the tip of the abdomen (see photos under that species).

The Downy Emerald appears quite dull in coloration when in flight compared to the more iridescent green abdomen of the Brilliant Emerald but caution needs to be applied. The Downy Emerald starts its adult life with brighter colours and the Brilliant Emerald’s coloration dulls as it ages. Additionally, the Downy Emerald tends to fly with its abdomen arched up from the base whereas Brilliant tends to fly with a flatter abdomen.

The Downy Emerald flies earlier than the Brilliant Emerald and the latter flies later in the year though there is considerable overlap so, again, caution needs to be applied when using this criterion for identification.

There are some behavioural differences between the two species though again care should be taken and not too much reliance placed on them.

The two Emerald Dragonfly species can be found at the same site, patrolling fairly sheltered heathland ponds or hawking high in the woodland canopy, rarely settling. As a result, distinguishing between them can be a frustrating task. The Downy Emerald usually goes for the more open areas, flying very low, regularly turning back and forth, and hovering. It appears shiny black in flight, except for the transparent wings. Both sexes have a bronze-green downy thorax and a dark metallic green abdomen, which is club-shaped in the male and rounded in the female. Young newly breeding adults have beautiful greenish yellow eyes and bronzey abdomens going duller with age. The female lacks the conspicuous ovipositor (vulvar scale) of Somatochlora metallica.

Cordulia aenea
1 / 7
teneral male
Photo: David Sadler
Cordulia aenea
2 / 7
female
Photo: David Sadler
Cordulia aenea
3 / 7
female
Photo: David Sadler
Cordulia aenea
4 / 7
male
Photo: David Sadler
Cordulia aenea
5 / 7
male
Photo: David Sadler
Cordulia aenea
6 / 7
male
Photo: David Sadler
Cordulia aenea
7 / 7
mating
Photo: David Sadler

National status
A nationally rare species, and listed in the British Red Data Book on Invertebrates. With a stronghold in south-east England, it has an otherwise scattered distribution from Devon to the Scottish Highlands.

Status in Sussex
Thinly but widely and inconsistently scattered across the county including the south east from where the 1965-1978 survey had no breeding records (Chelmick 1979). Listed in the Sussex Rare Species Inventory.

Distribution at 1km scale

Cordulia aenea distribution (all)
Cordulia aenea distribution bre 1980
Cordulia aenea distribution 1980 - 1989
Cordulia aenea distribution 1990 - 1999
Cordulia aenea distribution 2000 - 2009
Cordulia aenea distribution 2010 - 2019
Cordulia aenea distribution 2020 on

Historical records
All authorities (e.g. Lucas and Bloomfield 1905; Craven 1922) seem to agree that the first record for Sussex is by Unwin who found one near Horsham in June 1846. However, up until 1945 there had been only three localities recorded in West Sussex (Dannreuther 1945), and it seems to have fared only slightly better in East Sussex (Chelmick 1979). In the north and west of the county Chelmick (1979) considered it widespread and common.

Flight times
Early May - late July. The flight time appears to have moved forward slightly during the decade to 2020.

Phenology (adult)

Cordulia aenea phenology (all)
Cordulia aenea phenology pre 1980
Cordulia aenea phenology 1980 - 1989
Cordulia aenea phenology 1990 - 1999
Cordulia aenea phenology 2000 - 2009
Cordulia aenea phenology 2010 - 2019
Cordulia aenea phenology 2020 on
Cordulia aenea habitat
1 / 1
Downy Emerald habitat near Lavender Platt, Ashdown Forest
Photo: Simon Linington

Habitat
Preference for nutrient-poor, acidic, tree-lined or woodland (usually deciduous) ponds, lakes and canals. Occasionally, slow-flowing rivers and streams, with trees and overhanging branches.

Conservation
Since the larvae live in the slowly decomposing vegetation at the bottom of (usually still-water) body, dredging could pose a serious threat. A further threat comes from nutrient enrichment of water caused by run-off from adjacent cultivated land or fertilised pasture. Loss of woodland ponds or clearance of their tree-lined fringes poses problems for the adults.

Similar species
This species is only likely to be confused with the Brilliant Emerald in Sussex. Ultimately, identification boils down to the amount of yellow on the upper face (frons), the shape of the tail / anal appendages and in females, the presence or absence of a ‘vulvar scale’ that protrudes at right angles below the tip of the abdomen. Appearance in flight, flight times and behaviour are also pointers but not infallible.

The Downy Emerald lacks the extensive yellow on the frons of the Brilliant Emerald. The anal appendages of the male Downy Emerald are blunt and outward-pointing whereas those of the Brilliant Emerald are pointed and inward-pointing. The appendages of the female Downy Emerald are shorter than those of the Brilliant Emerald though being a relative difference this is of limited value. Thankfully, the Brilliant Emerald has a distinct vulvar scale below the tip of the abdomen (see photos under that species).

The Downy Emerald appears quite dull in coloration when in flight compared to the more iridescent green abdomen of the Brilliant Emerald but caution needs to be applied. The Downy Emerald starts its adult life with brighter colours and the Brilliant Emerald’s coloration dulls as it ages. Additionally, the Downy Emerald tends to fly with its abdomen arched up from the base whereas Brilliant tends to fly with a flatter abdomen.

The Downy Emerald flies earlier than the Brilliant Emerald and the latter flies later in the year though there is considerable overlap so, again, caution needs to be applied when using this criterion for identification.

There are some behavioural differences between the two species though again care should be taken and not too much reliance placed on them.