Among the Instars: Nehalennia irene
Hello bug folks! This week’s focus is on damselflies, slender insects with aquatic nymphs and winged adults who flit around near stream pools, lakes, and wetlands. They are closely related to dragonflies and fall within the same taxonomic order of Odonata. By appearance, they can look very different though. Nymphs are usually long and slender with three caudal lamellae (tails) at the end of the abdomen, and adults are similarly slender with two pairs of wings that are held either together along the back or out at an angle when at rest. Dragonflies, in contrast, are much chunkier in both life stages; nymphs have five points at the end of their abdomen rather than tails, and adults are thicker with wings held out horizontally when at rest. All odonates are voracious predators; nymphs will eat just about anything underwater including other insects, tadpoles, and small fish, and adults eat any flying insects they can catch while in flight themselves.
Nehalennia irene, a damselfly in the family Coenagrionidae
Characteristics of Nehalennia irene and related species
The image for this week is an example of a small damselfly found all across America: Nehalennia irene. This family (Coenagrionidae, also known as narrow-winged damselflies) is the most successful and widespread of all damselflies, which occur all over the world and in most freshwater habitats. The genus Nehalennia consists of five species in North America, with only two of those species occurring north of Florida: N. gracilis in the eastern half of the continent and N. irene widely distributed. I love the name Nehalennia and dove into that a bit further. Turns out, it’s named after a river goddess from the Rhine region. The origin of the name isn’t well defined, but one possible translation from Celtic is “she who is at the sea.”
Ecology
This particular species is known as a sedge sprite and the has distinct black spots along the edge of each lamellae, almost spreading into bands towards the tips. Adults are known to be small with metallic green and blue coloring, and they usually fly in and around dense vegetation in unpolluted marshes, bogs, fens, and ponds, making them difficult to spot.
Taxonomy of Nehalennia irene
Damselflies in this family are usually either my best friend or my worst nightmare to try and identify. Most often, specimens I’ve seen are very immature and can only be identified to the family level. Samples collected in September or October are the most likely to host these immatures. The other challenge is that genus level and further identification requires the lamellae to be intact. The extreme delicacy of these structures results in them breaking off either during life or the collection process. The keys I use most rely on lamellae structures and coloring for many of the key couplets, so a specimen missing tails usually can’t be accurately identified.
I haven’t seen this species in many samples, but much of that can be attributed to immature specimens and the fact that many of samples I’ve processed came from streams or rivers whereas this guy prefers still waters.
Do you have a favorite damselfly? Let me know in the comments below or contact me via email! This image will also available for purchase as a print in my shop.
Sources
Westfall, M.J. and M.L. May. 1996. Damselflies of North America. Scientific Publishers, Gainesville, Fl.
Wisconsin Odonata Survey: Nehalennia irene (wiatri.net)
Sedge Sprite (Family Coenagrionidae) | Field Station (uwm.edu)