Wednesday, October 15, 2008

Late sightings of Erythromma najas

The Red-eyed Damselfly (Erythromma najas) is a species of early summer, adults are mainly seen in late May and June.

Red-eyed Damselfly

Sightings in other months are not uncommon. Last year (2007), on the Dutch site sightings were reported from April 17. This year (2008) the first sighting was reported there on May 3.

But what about late sightings? Sightings in July and to a lesser extend August are not uncommon, although the number of sighted individuals declines. Personally I could report only a single imago in August this year and none in September. At the end of September somebody reported multiple individuals in an area quite close to where I have been watching dragonflies this year. Interesting information was that the number of individuals seemed to have slightly increased as compared with the previous weeks. These late Red-eyed Damselflies were not worn-out old individuals, they must have been emerged quite recently.

But even while paying extra attention to this species, "my" area looked still void of Red-eyed Damselflies. On October 11, I did some effort to get into the area of the reported sightings (it is private property and I don't want to enter that without permission). And yes, I was happy to spot one male. Although I did not succeed in taking a photo, it was exciting. But is it really that rare? Although most sites do not mention Erythromma najas as a species flying in October, British Insects (Watson, L., and Dallwitz, M.J.) says that "adults are on the wing from early May to early October.

It leaves us with some questions. It is not totally clear if this species has a one-year or two-year development cycle. Maybe it does not have a clearly defined seasonal cycle. The species is listed as a "trans-seasonal" species with an "asynchronous emergence" in some studies. I could not find a clear definition of these terms (so help me out if you can). So far I understand that although there is a clear seasonal peak, the species can get through the winter in different stages of development.

Also it seems that data from the UK show that in response to global warming, Erythromma najas is expanding its flight season in both directions: it is found both earlier and later in the season than in previous times. If global warming continues, we can probably expect more October sightings.

  • Historical changes in the phenology of British Odonata are related to climate (PDF)
  • Flight seasonality of dragonflies (insecta, odonata) in Northeastern Ukraine (PDF)
  • Saturday, October 4, 2008

    Some dragonflies in the Bohemian Paradise

    Last August (2008), I visited the Bohemian Paradise (Czech Republic). It was just for a holiday, not for a research project. On some days I have taken my camera and went searching for dragonflies. Here's a partly illustrated list of what I found.

    Aeshna cyanea
    Aeshna cyanea
    At several places I found the Southern Hawker (Aeshna cyanea). A small pond in the area of the Prachovský skály was full of them. Several patrolling males and a freshly emerged female.

    Sympetrum sanguineum
    Sympetrum sanguineum
    The Ruddy Darter (Sympetrum sanguineum) seems to be the most common Sympetrum species. I saw this species at many locations, including oviposition. The most common Sympetrum species in the Netherlands are S. vulgatum and S. striolatum - although the situation is of course dependent of the location.

    Somatochlora metallica
    Somatochlora metallica
    The Brilliant Emerald (Somatochlora metallica) is one of the species which still misses on my species list for the Netherlands. This one is photographed at the Sedmihorky pond.

    Aeshna mixta
    Aeshna mixta
    The Migrant Hawker (Aeshna mixta) is very common in the area.

    Ischnura pumilio
    Ischnura pumilio, male
    Ischnura pumilio, female
    There was a population of the Small Bluetail (Ischnura pumilio) at the edge of a pond with the name Komárovský rybník. This is another species which lacks on my list for the Netherlands. I was happy to photograph both male and female.

    Ischnura elegans
    Ischnura elegans
    The Blue-tailed Damselfly (Ischnura elegans) is a common species in the area.

    More species
    Some other species of which I did not take a decent photo.
    • Lestes viridis
    • Orthetrum cancellatum
    • Aeshna grandis
    • Sympetrum vulgatum
    • Calopteryx virgo, still missing on my list for the Netherlands as well.
    • Calopteryx splendens

    Friday, October 3, 2008

    My odonata report for 2008 (Netherlands)

    Now that the autumn has definitely arrived, it is time for a quick look back to my odonata observations of this year. It was my second dragonfly-year, I only started observing and photographing dragonflies in 2007.

    My main observation area was a semi-natural park just north of Utrecht (Netherlands) and my aim was not only to get an impression of the abundance of odonata species there, but also to make photos of each species. But I also looked a bit in other places.

    Winter Damselfly in February
    First thing that happened in 2008 was that I found a some Winter Damselflies (Sympecma fusca) on a location where they get through the winter. I was inspired to search them, when I read messages on a forum by people who had been finding them in relatively dry forest/heather fields. After looking on a map for suitable locations, I was happy to find about 10 adult Winter Damselfies on a sunny February day.

    Sympecma fusca

    My main observation area for 2008 was in the Noorderpark (also often called Gagelpolder). I concentrated on the area near the Ruigenhoek Fortress, but sometimes I looked in other parts of the area too. Throughout the year, I counted 25 different species in the Ruigenhoek area and one additional species from another part of the park. Here is the list of species, with some remarks. The date refers to the first sighting.

    Sympecma fusca (couple), laying eggs
    Sympecma fusca, oviposition
    Brachytron pratense
    Brachytron pratense
    Aeshna isoceles
    Aeshna isoceles
    Libellula quadrimaculata
    Libellula quadrimaculata
    Anax imperator
    Anax imperator, female
    Crocothemis erythraea
    Crocothemis erythraea, female
    Lestes viridis
    Lestes viridis
    Sympetrum vulgatum
    Sympetrum vulgatum
    • Pyrrhosoma nymphula (April 21). Quite a common species in the area.
    • Coenagrion pulchellum (April 26). The most abundant species in early spring.
    • Sympecma fusca (April 26). The Noorderpark is one of the few known locations near Utrecht where this species reproduces.
    • Ischnura elegans (May 2). This species is very common everywhere, no surprise.
    • Erythromma najas (May 3). Also common in the area and reproducing. In an area close by, fresh individuals have been observed in late autumn. But I have not seen any late individuals in the Noorderpark.
    • Brachytron pratense (May 3). The first anisoptera species at the location. Some exuviae indicated reproduction.
    • Libellula quadrimaculata (May 3). The most abundant anisoptera species in spring.
    • Cordulia aenea (May 3). Reproduces at the location.
    • Libellula depressa (May 10). Although a common species in the Netherlands, I only observed a few at this location. The location does not seem to provide the right habitat for this species.
    • Orthetrum cancellatum (May 12). Very common, most abundant anisoptera species in the summer.
    • Anax imperator (May 19). Easily recognized, in the summer there are always some around.
    • Aeshna isoceles (May 19). Quite common at the location.
    • Enallagma cyathigerum (June 2). Appeared quite late at this location, and although common since then even until September, I did not see the large numbers which can be found at other locations.
    • Lestes sponsa (June 10). During the year I spotted only a few individuals, but they appeared fresh. Around Utrecht city this species is not very common, but it looks like a small population is present at this location.
    • Sympetrum striolatum (June 10). Sometimes hard to tell apart from S. vulgatum. The latter species is very common at the location, but among them there are often one or a few S. striolatum individuals.
    • Lestes viridis (June 22). Common species in late summer and early autumn.
    • Sympetrum sanguineum (June 22). Always a few of them in summer.
    • Aeshna grandis (June 22). Easily recognized. Oviposition observed more than once.
    • Crocothemis erythraea (June 23). This species is still rare in the Netherlands although it is expected to become more common due to climate change. On two occasions I saw (and photographed) a female at the location.
    • Sympetrum vulgatum (July 4). Most common species at the location in late summer and autumn. It is hard to estimate numbers, but it would not surprise me if would be hundreds.
    • Erythromma viridulum (July 14). Enough of them in late summer, oviposition no exception.
    • Sympetrum flaveolum (august 3). This year there was an influx of S. flaveolum into the Netherlands. Some individuals ended up in the Noorderpark.
    • Aeshna mixta (August 6). Lots of them in late summer.
    • Aeshna cyanea (September 9). The only species I did not succeed to photograph at the location.
    • Sympetrum danae (September 11). There are some large populations not too far away, and it is not unexpected to have some individuals visit this location.

    As I mentioned, there was one more species which I only found in another part of the Noorderpark. That was Aeshna viridis, a rare species in the Netherlands (and even in Europe). I was happy to make this flight photo.
    Aeshna viridis

    New species on my list
    Four of the species above were new on my personal life list for the Netherlands: Crocothemis erythraea, Erythromma viridulum, Sympetrum flaveolum and Aeshna viridis. On other locations I did add some more new species to that list: Leucorrhinia rubicunda, Leucorrhinia dubia, Platycnemis pennipes and Lestes virens. The total length of my species list for the Netherlands is now 34. That is only about half of the species listed for the Netherlands. But although I keep track of the species, I am not much of a species hunter, but concentrate on areas close by.


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