Enallagma hageni
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| Enallagma hageni | ||||||||||||
| ( Walsh , 1863) |
Enallagma hageni is a species of dragonfly from the family of the common dragonfly (Coenagrionidae), which is widespread in Canada and northern North America and can become very common in northern latitudes. Open swamp areas, lakes and ponds with dense vegetation and also bog pools are settled. Enallagma hageni is a typical representative of the species-rich group of blue-colored cup maids . It is confusingly similar to the other members of the genus, especially the Enallagma ebrium, which is almost identical in ecological requirements. The first description of the species was made by Benjamin Then Walsh in 1863, the specific epithet honors the entomologist Hermann August Hagen .
features
Enallagma hageni is a typical slender dragonfly with a body length of 27 to 33 millimeters and a length of the hind wings of 15 to 21 millimeters and thus belongs to the small representatives within the group of blue-colored cup maids. The males have a light blue basic color with drop-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. On the upper side of the thorax there is a broad black median stripe with slightly narrower, light ante-humeral stripes on both sides. The following dark humeral stripes are of similar width. On the light blue sides of the thorax underneath there are two short black stripes, the upper one is, as is typical for the cup maids, only very rudimentary or not at all, so that the side surfaces appear as if they were not marked. The elongated abdomen is provided with a typical slender vial mark. At the lower end of the second segment there is a black point, which in most specimens merges with the adjacent caudal ring. There are also narrow black rings on the other segments three to five, which expand dorsally and increase in width towards the rear segments. Segments six and seven are predominantly black on the upper side, with the tapering drawing touching the ring of the segment in front. The eighth and ninth abdominal segments are unmarked and therefore blue, the tenth completely black on top.
The abdomen of the females is more powerfully built than that of the males and the top is completely covered with a black torpedo-shaped drawing, so that the abdominal segments only show a light ring at the front edge of segments three to eight. There is a protruding spike in front of the ovary on the eighth abdominal segment. 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 blue form, colored like the males, as well as the either pale brown or greenish colored heterochromic forms. The eyes of the females are divided horizontally in color, the lower part is brownish or greenish, the upper part brown. On the lower light part there is usually a dark horizontal stripe.
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 only formed from 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.
Males of Enallagma hageni can hardly be distinguished from those of Enallagma ebrium , a differentiation can only be made on the basis of the male abdominal appendages, the details of which can possibly be perceived when viewed from close up. In E. hageni , only a single horizontal spine can be seen in the lateral view, while in E. ebrium the cerci fork into two outgrowths of about the same length.
The females, too, are practically identical to the females of E. ebrium and can only be distinguished by the shape of the prothorax and its typical shape of the rear edge. In E. hageni , this is largely upward and bulges clearly above the thorax, while in E. ebrium the areas are flat.
The very similar males of Enallagma annexum , Enallagma boreale , Enallagma civile and Enallagma vernale are also very difficult to distinguish from Enallagma hageni , as well as from E. ebrium . However, these are significantly larger and, with the exception of E. civile , the mushroom-shaped pattern of the second abdominal segment does not merge with the adjoining ring , at least in the area where the distribution overlaps with E. hageni . Other common blue slender vials are characterized by larger black portions on the middle abdominal segments. The females of E. hageni can also be confused with the females of Enallagma anna , Enallagma carunculatum , Enallagma civile and Coenagrion resolutum , which also have a completely black upper side of the abdomen.
distribution
The distribution area of Enallagma hageni extends west of the Rocky Mountains from the southern Northwest Territories to Wyoming and east over Maryland and Indiana to Nova Scotia ; in mountainous regions south to Georgia .
Odonatological records by Francis Whitehouse from 1918 for Alberta , in which species such as Enallagma carunculatum , Enallagma clausum and Enallagma ebrium and also Enallagma hageni are missing, suggest that they have expanded their territory significantly to the north in recent decades need to have.
Way of life
Enallagma hageni can become very common in the northern latitudes. Open swamp areas, lakes and ponds with dense vegetation and also bog pools are settled. In the north, E. hageni is usually the most common dragonfly species in large lakes.
The males rest on stalks of the swamp vegetation or algae mats near the water and fly - typical for the cup maids - over the open water. The dragonflies gather near the water to mate, the mating wheels reach the reproductive water in the afternoon. The mating takes an average of 22 minutes, then the dragonflies remain in tandem for an average of 58 minutes until they lay eggs. According to DuBois, the eggs are laid with the male attached without the female completely submerging. Paulson, on the other hand, states that the female usually goes underwater without a male attached and spends up to half an hour laying eggs in various floating dead or living plant stems. The males usually stay above the surface of the water and wait for the females to reappear, but mating with other searching males often occurs and reaches the resurfaced females first and pulls them out of the water. It takes three weeks for the larvae to hatch, their development takes almost a year, with overwintering in one of the last larval stages.
The flight time of the adults differs with the distribution. In the northwest of the range in British Columbia it lies between June and July, in Alberta it extends into August and in Nebraska until September. E. hageni hatches in Ontario in May and flies into September, in Québec and Wisconsin from June to September and in New York between May and August.
Naming
The first description of the species as Enallagma hageni , which is valid today, was made in 1863 by Benjamin Dann Walsh . The specific epithet , from which the American common name " Hagen's Bluet " is derived, honors the Prussian entomologist Hermann August Hagen , who published a large part of his work on North American dragonflies before he was ever in America. The naming by the amateur entomologist Walsh, who also translated one of Hagen's manuscripts from French into English, came before Hermann August Hagen came to America to teach at the University of Cambridge / Massachusetts and later at Harvard University.
swell
literature
- John Acorn: Damselflies of Alberta, Flying Neon Toothpicks in the Grass. University of Texas Press, Austin 2011, ISBN 978-0-88864-419-0 .
- 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 0-691-12281-4 .
- Robert DuBois: Dragonflies & Damselflies of the Rocky Mountains. Kollath + Stensaas Publishing, Duluth 2010, ISBN 978-0-9792006-8-7 .
Individual evidence
- ↑ a b c d e f g h Dennis Paulson: Hagen's Bluet. In: Dragonflies and Damselflies of the East. Pp. 104-105.
- ^ 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.
- ↑ a b c Robert DuBois: Hagen's Bluet. In: Dragonflies & Damselflies of the Rocky Mountains. Pp. 116-117.
- ↑ Robert DuBois: Marsh Bluet. In: Dragonflies & Damselflies of the Rocky Mountains. Pp. 114-115.
- ^ Dennis Paulson: Marsh Bluet. In: Dragonflies and Damselflies of the East. Pp. 103-104.
- ↑ a b Dennis Paulson: Hagen's Bluet. In: Dragonflies and Damselflies of the West. P. 91.
- ↑ a b John Acorn: Hagen's Bluet. In: Damselflies of Alberta. Pp. 92-94.
Web links
- Photos of "Enallagma hageni" - Hagen's Bluet on odonata.bogfoot.net, with pictures