The obelisk posture is a
handstand
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A handstand is the act of supporting the body in a stable, inverted vertical position by balancing on the hands. In a basic handstand, the body is held straight with arms and legs fully extended, with hands spaced approximately shoulder- ...
-like position that some
dragonflies
A dragonfly is a flying insect belonging to the infraorder Anisoptera below the order Odonata. About 3,000 extant species of true dragonfly are known. Most are tropical, with fewer species in temperate regions. Loss of wetland habitat threa ...
and
damselflies
Damselflies are flying insects of the suborder Zygoptera in the order Odonata. They are similar to dragonflies, which constitute the other odonatan suborder, Anisoptera, but are smaller and have slimmer bodies. Most species fold the wings along ...
assume to prevent overheating on sunny days. The
abdomen
The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the torso. ...
is raised until its tip points at the sun, minimizing the surface area exposed to solar radiation. When the sun is close to directly overhead, the vertical alignment of the
insect
Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pairs ...
's body suggests an
obelisk
An obelisk (; from grc, ὀβελίσκος ; diminutive of ''obelos'', " spit, nail, pointed pillar") is a tall, four-sided, narrow tapering monument which ends in a pyramid-like shape or pyramidion at the top. Originally constructed by Anc ...
.
Function and occurrence
Dragonflies may also raise their abdomens for other reasons. For instance, male
Blue Dasher
The blue dasher (''Pachydiplax longipennis'') is a dragonfly of the skimmer family. It is the only species in the genus ''Pachydiplax''. It is very common and widely distributed through North America and into the Bahamas.
Although the species nam ...
s (''Pachydiplax longipennis'') assume an obelisk-like posture while guarding their territories or during conflicts with other males, displaying the blue
pruinescence Pruinescence , or pruinosity, is a "frosted" or dusty-looking coating on top of a surface. It may also be called a pruina (plural: ''pruinae''), from the Latin word for hoarfrost. The adjectival form is pruinose .
Entomology
In insects, a "blo ...
on their abdomens to best advantage.
[Corbet, 285-287.][Clifford, 192-193.] However, both females and males will raise their abdomens at high temperature and lower them again if shaded. This behavior can be demonstrated in the laboratory by heating captive Blue Dashers with a 250 watt lamp, and has been shown to be effective in stopping or slowing the rise in their body temperature.
Celithemis eponina
The Halloween pennant (''Celithemis eponina'') is a species of dragonfly in the family Libellulidae. It is native to eastern North America, including Ontario in Canada and the United States as far west as Colorado.NatureServe. 2015''Celithemis ...
'' in the obelisk posture
Dropwing (Trithemis selika) young male obelisk composite.jpg, young male ''T. selika'' moving into obelisk posture
Pachydiplax longipennis Blue Dasher 1500px.jpg, Blue Dasher: a raised abdomen may be either a response to heat or a threat display
The obelisk posture has been observed in about 30 species in the
Demoiselle,
Clubtail, and
Skimmer families. All are "perchers"—sit-and-wait predators that fly up from a perch to take prey and perch again to eat it. Since they spend most of their time stationary, perchers have the most opportunity to
thermoregulate
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperature ...
by adjusting their position.
Other forms of postural thermoregulation
Some species, including the
Dragonhunter (''Hagenius brevistylus''), reduce exposure to the sun by perching with the abdomen pointed downward, rather than upward. The tropical
skimmer dragonfly ''Diastatops intensa'', whose wings are mostly black, points its wings rather than its abdomen at the sun, apparently to reduce the heat they absorb.
While flying, some Saddlebags Gliders (genus ''
Tramea
''Tramea'' is a genus of dragonflies in the family Libellulidae,
the skimmers and perchers. Species of ''Tramea'' are found in tropical and subtropical regions around the globe.
They typically have colored bases to their otherwise translucent hi ...
'') lower their abdomens into the shade provided by dark patches at the bases of their hindwings. The same behavior has been observed in ''
Pseudothemis zonata'', which has a similar hindwing patch.
Dragonflies also use postural thermoregulation to increase body temperature. Keeping the flight muscles in the
thorax
The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the cre ...
warm is especially important, since otherwise the insect cannot fly. Dragonflies may position their wings to reflect sun onto themselves, or, if they are perched on a warm surface, to form a "greenhouse" over the thorax. When the sun is low in the sky, they may raise or lower their abdomens so that their bodies are perpendicular to the sun's rays, maximizing the surface area that receives direct sun; although this can resemble the obelisk posture, the purpose is opposite.
Notes
References
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*
*
Further reading
* {{cite book , author = Heinrich, Bernd , title = The Thermal Warriors: Strategies of Insect Survival , publisher = Harvard University Press , location = Cambridge , year = 1999, pages = 66–67 , isbn = 0-674-88341-1
Ethology
Odonata