Lake darner (Aeshna eremita)

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Lake darner fact file

• Description
• Biology
• Range
• Habitat
• Status
• Threats
• Conservation
• Find out more
• Glossary
• References
• Print factsheet

Lake darner description

A large and brightly coloured dragonfly, the lake darner (Aeshna eremita) is the largest Aeshna species in North America ^{(2) (3) (4) (5)}. Like other darners, the lake darner has clear wings and large eyes that meet on top of the head ^{(5) (6)}. Its abdomen is long and slender ^{(2) (5)} and somewhat resembles a darning needle, giving this species its common name ⁽⁵⁾.

The male lake darner has a pair of blue to green stripes on either side of its brown thorax, with a pale spot or streak between the stripes and a rounded notch in the middle of the stripe nearest the head ^{(2) (3) (5)}. The lake darner’s face is yellow-green with a black line across it ^{(3) (4) (5)}, and the eyes are turquoise ⁽²⁾. Aeshna species are often known as ‘mosaic darners’ due to the mosaic-like pattern of blue spots along the top of the abdomen ^{(2) (3) (5)}. In the male lake darner, these spots are usually blue on a brown background ⁽³⁾, and may appear darker at cool temperatures ⁽⁵⁾.

The female lake darner is slightly smaller than the male ^{(3) (4)} and is variable in colouration. Most females have green or yellow-green stripes and spots, but a few have similar blue markings to the male ^{(2) (3) (4) (5)}. Intermediate females with green spots on the top of the abdomen and blue spots on the sides also occur ⁽⁵⁾.

Although similar in appearance to the related Canada darner (Aeshna canadensis), the lake darner can be distinguished by its larger size, the black line across its face, the notch in its thorax stripe, and a lack of pale spots beneath the abdomen ^{(2) (4) (5)}.

Size

Length: 6.6 - 7.9 cm ^{(2) (3)}

Hind wing length: 4.1 - 5.2 cm ^{(2) (3)}

Lake darner biology

A strong flier ⁽³⁾, the adult lake darner may be active throughout the day and continue flying until dark ⁽²⁾. In the far north of its range, it may even be active under the midnight sun ^{(2) (5)}. Like other darner species, the lake darner hangs in a characteristic vertical position when perched ^{(2) (5)}, but unlike most other darners it does not hover during flight ^{(2) (6)}.

The male lake darner is not territorial, and it flies over open water or along lake shores in search of females with which to mate. It usually avoids entering vegetation, except when searching for a female ^{(2) (6)}. As in other dragonflies, the male lake darner may guard the female while the eggs are laid, to prevent her from mating with other males ^{(8) (9)}.

The female lake darner has a well-developed ovipositor, a tube-like structure at the end of the abdomen which is used to lay the eggs. As in other Aeshnidae species, the female lake darner is able to use the ovipositor to slice into water plants and lay eggs one at a time into the stems ^{(2) (3) (5) (6)}. The eggs are also sometimes laid onto floating logs or in root tangles at or just below the water’s surface ^{(2) (6)}.

The larvae of the lake darner, known as nymphs, have a streamlined body shape and excellent eyesight. They are opportunistic and voracious predators, often climbing aquatic vegetation to stalk their prey and attacking any animal smaller than themselves ⁽³⁾, including insect larvae, small crustaceans, tadpoles and even small fish ^{(6) (8)}. As in all dragonflies, the larva of the lake darner catches its prey by shooting out the fiercely hooked lower jaw, known as the labium, which impales the victim and drags it back to the mouth ^{(8) (9)}. The larvae of most Aeshna species take about two to four years to develop into adults ⁽³⁾.

The flight season of the lake darner, when the adults emerge and are active, usually runs from June to October ^{(2) (3) (4) (5)}. Like the larva, the adult lake darner is an opportunistic predator and will catch almost any soft-bodied flying insect ⁽⁶⁾.

Lake darner range

The lake darner occurs across northern parts of North America, from Alaska east to Labrador and Newfoundland in Canada, and south to New York, Massachusetts, Michigan, Wisconsin, Minnesota, North Dakota, Colorado, Utah and Washington in the United States ^{(2) (3) (4) (7)}.

Lake darner habitat

The lake darner typically inhabits wooded or sparsely vegetated lakes and ponds, although it can also be found around marshes, bogs, fens and slow-flowing streams ^{(2) (3) (4) (5) (6)}. This species feeds around forest openings and may perch on tree trunks, branches or sometimes on the ground ^{(2) (4) (5) (6)}.

Lake darner status

The lake darner has yet to be classified by the IUCN.

Lake darner threats

No major threats to the lake darner are currently known. However, in parts of its range the wetland habitats on which many dragonflies rely have been heavily impacted by human activities, such as increasing development and flood control measures ⁽³⁾.

Lake darner conservation

There are no specific conservation measures currently known to be in place for the lake darner.

Find out more

Find out more about the lake darner:

• Montana Field Guide - Lake darner:
  http://fieldguide.mt.gov/detail_IIODO14060.aspx

More information on dragonflies and on insect conservation in North America:

• Moore, N.W. (1997) Dragonflies: Status Survey and Conservation Action Plan. IUCN/SSC Odonata Specialist Group, IUCN, Gland, Switzerland and Cambridge, UK. Available at:
  http://data.iucn.org/dbtw-wpd/edocs/1997-042.pdf
• The Xerces Society:
  http://www.xerces.org/

Authentication

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
arkive@wildscreen.org.uk

Glossary

Abdomen

In arthropods (crustaceans, insects and arachnids) the abdomen is the hind region of the body, which is usually segmented to a degree (but not visibly in most spiders).

Crustaceans

Diverse group of animals with jointed limbs and a hard chitinous exoskeleton, characterised by the possession of two pairs of antennae, one pair of mandibles (mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, woodlice and barnacles.

Larvae

Stage in an animal’s lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.

Nymph

Stage of insect development, similar in appearance to the adult but sexually immature and without wings. The adult form is reached via a series of moults and the wings develop externally as the nymph grows.

Ovipositor

The egg-laying organ of a female insect, consisting of a tube-like structure at the end of the abdomen. In worker bees and non-reproductive female wasps, it is modified into a sting.

Territorial

Describes an animal, a pair of animals or a colony that occupies and defends an area.

Thorax

Part of the body located between the head and the abdomen in animals. In insects, the three segments between the head and the abdomen, each of which has a pair of legs.

References

1. Integrated Taxonomic Information System (ITIS) (August, 2012)
   http://www.itis.gov/
2. Paulson, D. (2009) Dragonflies and Damselflies of the West. Princeton University Press, Princeton, New Jersey.
3. Proche, J. and Runyan, S. (1996) Dragonflies of the Family Aeshnidae in British Columbia: Biological Notes and Field Key, Based on Specimens in the Royal British Columbia Museum Collection. Royal British Columbia Museum, Victoria, British Columbia. Available at:
   http://www.royalbcmuseum.bc.ca/content_files/files/aeshnidae_of_bc.pdf
4. Royal British Columbia Museum and the Spencer Entomological Museum (2004) Aeshna eremita (Lake Darner). In: Odonata Distribution Maps Based on Data from the Royal British Columbia Museum and the Spencer Entomological Museum. Royal British Columbia Museum and Conservation Data Centre, Victoria, British Columbia. Available at:
   http://www.env.gov.bc.ca/wld/documents/odonates/IO_AESERE.pdf
5. Dunkle, S.W. (2000) Dragonflies through Binoculars: A Field Guide to Dragonflies of North America. Oxford University Press, New York.
6. Montana Field Guide - Lake darner (August, 2012)
   http://fieldguide.mt.gov/detail_IIODO14060.aspx
7. Paulson, D. (2011) Dragonflies and Damselflies of the East. Princeton University Press, Princeton, New Jersey.
8. Moore, N.W. (1997) Dragonflies: Status Survey and Conservation Action Plan. IUCN/SSC Odonata Specialist Group, IUCN, Gland, Switzerland and Cambridge, UK. Available at:
   http://data.iucn.org/dbtw-wpd/edocs/1997-042.pdf
9. O'Toole, C. (2002) The New Encyclopedia of Insects and their Allies. Oxford University Press, Oxford.