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Obelisk posture
The obelisk posture is a handstand-like position that some dragonflies and damselflies assume to prevent overheating on sunny days. The abdomen 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's body suggests an obelisk.
==Function and occurrence==
Dragonflies may also raise their abdomens for other reasons. For instance, male Blue Dashers (''Pachydiplax longipennis'') assume an obelisk-like posture while guarding their territories or during conflicts with other males, displaying the blue pruinescence 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.〔
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 by adjusting their position.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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