This time, a blog post about a damselfly that is very common in the Netherlands. Perhaps even the most common species in our country: the blue-tailed damselfly (Ischnura elegans). This small blue damselfly can be found in almost any body of water, whether it’s a tiny garden pond, on the shores of a lake or small forest pond. This species seems to feel at home everywhere, especially in nutrient-rich, clear freshwater with some variety in vegetation along the banks. Sometimes you can even find them in brackish water and polluted water doesn’t seem to bother this damselfly either. Something other dragonfly and damselfly species tend to avoid.

Bluetails

This damselfly belongs to the genus of bluetails (Ischnura), also known as forktails, of which 72 species occur worldwide. They are part of the family of so-called pond damselflies (Coenagrionidae), which includes 1,143 different species worldwide. This makes it the largest dragonfly family worldwide. With fifteen species, this family also represents a significant portion of native dragons and damsels in the Netherlands. Well-known representatives of this family include the azure damselfly (Coenagrion puella), the large red damselfly (Pyrrhosoma nymphula), and the small red damselfly (Ceriagrion tenellum).

Scarce blue-tailed damselfly

Characteristic for the blue-tailed damselfly is the bright blue eighth segment of its abdomen, the lantern. This is where this damselfly gets its Dutch name lantaarntje from. The rest of the abdomen is completely dark to black. All members of the genus Ischnura have a blue-coloured segment on the abdomen, in most cases the eighth or ninth. Besides the blue-tailed damselfly, there is only one other damselfly from this genus in the Netherlands, namely the scarce blue-tailed damselfly (Ischnura pumilio), see also the photo alongside. This is a relatively rare species that is on the rise from the south. I saw and photographed it in the summer of 2024. The male of this species also has a bright blue segment, but only the ninth and a small part of the eighth. Confusion with the blue-tailed damselfly is therefore possible. In the females, the difference between the blue-tailed damselfly and the scarce blue-tailed damselfly is clearer. Because the latter lacks the blue segment on the abdomen, which is not the case with the female blue-tailed damselfly.

More or less blue

Because of that black abdomen and only the bright blue penultimate segment, it’s almost impossible to confuse it with any of the other common blue damselflies, such as the aforementioned azure damselfly, the variable damselfly (Coenagrion pulchellum) and the common blue damselfly (Enallagma cyathigerum). Their abdomens are black, with some species showing more blue than others, which is one of the key distinguishing characteristics. But none of these species has a black abdomen with only one blue segment. Incidentally, the thorax of the female blue-tailed damselfly can be — in addition to blue — green, purple, orange, or brown. And there are colour variants where the female not only has a brown thorax, but also a brown lantern. This variant has the advantage that the female is much less conspicuous to predators. In the blue colour variant, the females look very similar to the males, with a blue thorax and a blue lantern.

Mating for hours

The blue-tailed damselfly flies from May to September, and during that time, it mates vigorously. Adult blue-tailed damselflies don’t live very long: males average five days, while females last a maximum of eleven. Mating is quite a challenge, as it can last several hours. Sometimes even up to seven hours! And it takes so long for a reason. The first thing the male does during mating is remove the sperm of any competitor who has previously mated with the female. This way, he can be sure that it’s his offspring that will soon be flying around. Although that’s never certain in this case, another male could mate with the female after he has. The female lays eggs alone, not in tandem, as is the case with most other damselfly species. Because the female is on her own, another male could easily appear between mating and egg laying, who in turn will mate with the female.

Troublesome males

The eggs are usually laid in floating, dead plant material. But the female also uses living plants that protrude above the water. She often lays her eggs late in the day, when the male population is calmer and she’s not constantly being harassed. This is why mating often takes so long. The longer a male holds onto the female during mating until late in the day, the less likely she is to be fertilised by another male. The blue colouration, which makes a female resemble a male, does work to her advantage in this regard. They appear to be less harassed by males.

Cannibalistic larvae

The larvae emerge relatively quickly after laying eggs. Just like all damselflies and dragonflies, the larvae feed on other aquatic organisms, such as fly and mosquito larvae. They also feed on larvae of their own species and other damselfly species. The larvae usually remain in the water for a year and overwinter there. Under very favourable weather conditions (and sufficient food in the water, of course), larval development can take as little as three months. This second generation of damselflies then emerges at the end of summer and can sometimes be seen until October. This has been observed in other countries, and it’s likely that this second generation also occurs sporadically in the Netherlands. As temperatures rise, this phenomenon is likely to become more common.

Graceful abdomen

The scientific species name of the blue-tailed damselfly literally means “graceful abdomen.” The genus name Ischnura comes from the Greek ischnos = thin and ura = tail. And the species name elegans comes from Latin and says it all: it naturally means elegant or graceful. The blue-tailed damselfly certainly has a graceful abdomen, just like other members of the damselfly family. The scientific name was first described in 1820 by the Belgian entomologist Pièrre Léonard Vander Linden (1797-1831). Between 1820 and 1825, he published several scientific articles on dragonflies. Initially, Vander Linden did not consider the bluetails a separate genus but classified them within the larger family of pond damselflies. This family was then called the Agrionidae, which is why the blue-tailed damselfly initially had the scientific name Agrion elegans. Later the bluetails were classified into a separate genus under the pond damsels.

Sources and more information:

• British Dragonfly Society
• Wikipedia
• Grunsven, Roy van – Strijd tussen de seksen bij lantaarntjes – Vlinders 4 – 2023 “Battle of the sexes in blue-tailed damselflies” (in Dutch)
• Katsman, J. – Fotogids van de Libellen van Nederland – Eerste druk 2019 (in Dutch)
• Bos, F. – Wasscher, M. – Reinboud, W. – Veldgids Libellen – KNNV Uitgeverij – Zesde druk 2012 (in Dutch)