Enallagma boreale
| Enallagma boreale | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Enallagma boreale , male |
||||||||||||
| Systematics | ||||||||||||
|
||||||||||||
| Scientific name | ||||||||||||
| Enallagma boreale | ||||||||||||
| Selys , 1875 |
Enallagma boreale is a species of dragonfly from the family of the common dragonfly (Coenagrionidae), which is distributed in large parts of Canada and North America and can be very common in northern latitudes. Ponds and peripheral areas of larger lakes are populated with high proportions of vegetation protruding from the water. Enallagma boreale is a typical representative of the numerous group of blue-colored cup maids and is confusingly similar to the other members, especially the Enallagma annexum, which also has almost the same ecological requirements. The epithet boreal is derived from ancient Greek βορέας boreas what "cold" means and at the same time on Boreas refers, the Greek god of wintry north wind, and was the first to describe Edmond de Selys-Longchamps chosen as an indication of the distribution area.
features
Enallagma boreale is a typical slender dragonfly with a body length of 28 to 36 millimeters and a length of the rear wing of 17 to 22 millimeters. The males have a light blue basic color with large teardrop-shaped and also blue postocular spots on the body-facing side of the compound eyes . These are aligned with one another with the tip and connected to one another via a line. The eyes are dark on top, so that they appear to be covered by a cap. The median stripe on the upper side of the front body ( thorax ) is noticeably wide, while the lateral humeral stripes are narrow. On the underlying light blue thorax sides there are two thorax lateral stripes, the upper one is only very rudimentary or not at all, so that the thorax side surface appears as if it were not drawn. The elongated abdomen is provided with a typical slender vial mark. The lower end of the second segment has a broad, black, umbrella-shaped curved horizontal line, which in some specimens can extend to the end of the segment. In the case of representatives in the east of the distribution area, this horizontal line is significantly larger. On the other segments three to five there are black rings at the caudal end, the widest on the fifth segment. The majority of segments six and seven are black, the eighth and ninth abdominal segments are completely blue, and the tenth is black on top.
Northern populations, especially in the highlands of Alaska and Canada, have a much more extensive black pattern, the humeral stripes are significantly wider, the ante-humeral stripes can be broken. The drawing of the second abdominal segment looks like a large spot and touches the rear edge of the segment. The drawing of the middle abdominal segments is enlarged, more than half of the fourth and fifth segments are blackened. Some populations have a conspicuous irregular black markings on the sides of the eighth segment, which is actually blue.
The abdomen of the females is more powerfully built than that of the males and the upper side is predominantly dark in color, the abdominal segments only show a light ring at the front edge of segments three to eight. In front of the ovary, on the eighth abdominal segment, there is a protruding thorn. The light basic color of the dragonfly is most pronounced on segment eight, this can sometimes even be completely without black markings. Segments nine and ten are black. The eyes of the females are divided horizontally in color, the upper part is dark, the lower light brown, on the lower light part there is usually a dark horizontal stripe. The chest drawing corresponds to that of the male. As is not uncommon in the subfamily of the Ischnurinae , the females come in different color variants. There is an androchromic form, colored like the males, and a brown, heterochromic form.
Similar species
A relatively recent evolutionary split has led to a large number of species, some of which are very similar and difficult to distinguish, in North America. However, the cup youngsters are often formed from only one species, and once determined, it can be assumed that all specimens of this population only belong to this species. Preferences for different habitat types, which at first glance appear very similar, seem to separate them, even if these mechanisms are not yet fully understood.
Enallagma boreale and Enallagma annexum , whose distribution areas overlap over a large area, form a pair of species that cannot be distinguished in the field. Enallagma boreale and Enallagma annexum , as well as the likewise very similar Enallagma vernale, can only be distinguished by examining the male abdominal appendages, which differ in fine details . In E. annexum , a lip-shaped elevation can be seen in the enlargement of the male abdominal appendages; in E. boreale this is located on the inside of the cerci.
Enallagma civile is also very difficult to distinguish from Enallagma boreale , but its range only overlaps to a small extent with that of E. boreale . E. civile has longer upper abdominal appendages than lower ones, exactly the opposite of E. boreale, and the postocular spots and the markings on the upper side of the second abdominal segment that touch the posterior end of the segment are larger. Also Enallagma hageni and Marsh Bluet whose distribution areas rather with that of boreal Enallagma cover, you resemble, but are generally smaller with smaller Postokularflecken and have larger spots on the second abdominal segment. The male abdominal appendages also allow clear identification. With Enallagma clausum , the markings on the middle abdominal segments are usually less pronounced. The distribution overlaps with Enallagma carunculatum in some areas, but the males can be easily distinguished by the extent of the blackening of the middle abdominal segments and the different abdominal appendages.
The females of Enallagma boreale and Enallagma annexum are also very similar, a determination can be made by comparing the prothorax and its typical shape of the posterior margin. This is clearly developed in E. annexum , while in E. boreale it fuses with the thorax. The distinctly bright eighth abdominal segment does not occur in the females of other similar cup maids.
distribution
Enallagma boreale is distributed throughout western North America, the range extends from Alaska to the Mexican highlands of Durango , in the east it ranges from Labrador in the north to Iowa and West Virginia . E. boreale is less common than E. annexum along the immediate Pacific coast, and drier regions are generally preferred. In the south of the distribution area, mainly higher areas are settled.
Way of life
Enallagma boreale can become very common in northern latitudes. Ponds and the edge areas of larger lakes are populated with high proportions of vegetation protruding from the water, including cold tundrator bogs. In the east, E. boreale is apparently restricted to fish-free waters, not so in the west. The males can be found in large numbers near the water - typical of the cup maid - where they fly low over the open water in large numbers and rest in emersed vegetation . Pairs sometimes form far away from the water, often in open corridors in forest areas. Copulation lasts on average 23 minutes, followed by a search for suitable egg-laying sites. The eggs are laid in tandem and can also be continued under water. The average life expectancy of mature and reproductive adults is four days with a maximum of 17 days.
The flight time differs with the spread. In Yukon it is between May and July, in British Columbia it is between April and September. On the southern edge of the range in Arizona, it lasts from June to October. In the northeast of North America in Nova Scotia it lies between May and September and extends on the southern edge of the range, in Ohio , until June.
swell
literature
- Dennis Paulson: Dragonflies and Damselflies of the East, Princeton Field Guides , Princeton University Press, New Jersey 2011, ISBN 978-0-691-12283-0 .
- Dennis Paulson: Dragonflies and Damselflies of the West, Princeton Field Guides , Princeton University Press, New Jersey 2000, ISBN 978-0-691-12281-6 .
Individual evidence
- ↑ a b c d Dennis Paulson: Boreal Bluet. In Dragonflies and Damselflies of the West , pp. 88-90.
- ↑ a b c d e f g Dennis Paulson: Boreal Bluet. In Dragonflies and Damselflies of the East , pp. 98-99.
- ^ Jill Silsby: Subfamily Ischnurinae (Blue-tailed Damselflies). In Dragonflies of the World . Smithsonian, Washington 2001, ISBN 1-560-98959-9 , pp. 110-112.
- ^ A b Dennis Paulson: American Bluets. In Dragonflies and Damselflies of the East , p. 85.
- ^ Dennis Paulson: Vernal Bluet. In Dragonflies and Damselflies of the East , pp. 97-98.
- ^ Dennis Paulson: Northern Bluet. In Dragonflies and Damselflies of the East , pp. 95-97.
Web links
- Photos of Enallagma boreale - Boreal Bluet on odonata.bogfoot.net, with pictures