One of a series of Web pages by Roy J. Beckemeyer devoted to ASPECTS OF INSECT BIOLOGY.
Last updated 9 December 2003
©2003 by Roy J. Beckemeyer. This information is pending publication. Please do not copy or use in any published format or venue. This is the first of a series of pages that will be devoted to flight-related morphology of Anax junius.
Above right: In addition to the obvious color differences in males and females, there are body composition and relative proportion differences that relate to the different physiological and behavioral requirements of the two sexes. This pair of Common Green Darners is staying in tandem while the female oviposits so that the male can prevent other males from mating with her. Photo taken by Roy Beckemeyer at Quivira NWR, Stafford Co., Kansas.
Here are some measurements of male and female Anax junius that I made from specimens taken in Sedgwick County, Kansas during August, 1998.
|Property||Sex||Fore Wing Mass - mg||Hind Wing Mass - mg||Mass of Head - mg||Mass of Thorax - mg||Mass of Abdomen - mg||Total Mass - mg|
|Property||Sex||Flight Muscle Mass - mg||Total Lipid Mass - mg||Area of Fore Wings - sq mm||Area of Hind Wings - sq mm||Wing Loading - N/sq m|
|Mean||Male||435.80||25.60||949.0||1224.8||4.03||*Nr's in red|
|Std. Dev.||Female||48.0||53.9||97.1||65.5||0.77||revised 12/9/03|
The females are larger and more massive overall, with most of their mass concentrated in the abdomen. They have more fat, most of it in the abdomen, and associated with ovaries. They also have larger hind wings in proportion to their fore wings, at least in part to accommodate an aft shift in center of gravity relative to the males. The next bar chart compares the hind to fore wing ratios:
The next two pie charts compare the mass distributions by body part of the males and females. Note that the female mass is in her abdomen, the male's in his thorax:
Much of the male's mass is in his flight muscles, as can be seen in the next chart:
There is also a significant difference in tissue type, as shown in the next chart:
Detailed information on center of gravity of male and female Anax junius will eventually be posted here. For now, I will just note that in both sexes I have found the c.g. to be located aft of the hind wing leading edge at the "wing attach point" (location of the junction of the anterior veins with the axillary plate).
|n = 3 females, n = 4 males||Fresh Mass||Air Dry Mass||Lean Dry Mass|
|Female Mean||1102.90 mg||441.37 mg||371.73 mg|
|Female Std. Dev.||222.25 mg||108.93 mg||83.89 mg|
|Male Mean||895.20 mg||312.33 mg||293.75 mg|
|Male Std. Dev.||86.99 mg||28.49 mg||29.02 mg|