Black Hawk Down

Most people have seen the couples – two united in close formation, one being pulled along by the other. Perhaps you have seen them embracing, forming a romantic heart shape while resting on a reed. Someone may pipe out, “Hey! What are those two doing?” And there will always be someone nearby who will sagely reply, “They’re just mating, sonny…birds an’ the bees, ya know…”, and then they’ll move along, as if they had actually answered the question. Most people have seen these mating formations, but do they actually know what is occurring?

Black Meadowhawks Coupling

By human standards, dragonfly mating is complicated. Note that I refuse to draw analogies to humans after this point – I’ll leave that up to your imagination.

Dragonfly morphology

The male dragonfly has his genitalia behind his legs, sort of where we expect them to be. The problem is, his testes are back at the end of his abdomen, a good distance away. The question arises – how does he get the sperm from his testes (the primary genitalia) to his secondary genitalia where the penis is? There is no internal plumbing for this, so the male prepares for mating by curving his abdomen under and transferring sperm from the tip of his abdomen to a small pouch at the base of the secondary genitalia. In essence what you have is the male inseminating himself before he can even begin the action of inseminating a female.

Once the male is ‘armed’, and he can venture out in search of a mate.  At the the tip of his abdomen are three claspers – anal appendages (two ‘cerci’ and a central ‘epiproct’) that are used to capture his mate. When he spots a likely female he will dart down and, using the claspers, he will grip the female firmly behind the head and then take off with her. At some point the female will curve her abdomen down and then up to the males secondary genitalia. In this position,  called the missionary heart or wheel formation, sperm will be transferred the female’s genital opening where the eggs will be fertilized.  Once fertilized, the eggs can be laid immediately. The couple flies over water or the shoreline and the female taps down the ovipositor to deposit the eggs. In other species, the  females may have a saw or blade-like ovipositor which allows her to lay eggs in plants stems or in mud.

Detail showing ridge

If you have a closer look at the female in this image of Black Meadowhawks (Sympetrum danae), you will notice two rust-colored disks behind the female’s head. When I sent this photo to AlbertaBugs for I.D., I questioned what they were, because I had never noticed these structures before. It was speculated that this ridged plate functions to guide the claspers to the mesostigmal plates, as these structures are only found on the female. Knowing this now, I will try to obtain a better angle when photographing this clasping area next time.

(Thanks to Adam Blake for the I.D. and Terry Thormin for confirmation. Jason J. Dombroskie provided information on the ridged plate. Photo taken with Nikon D70 with 90mm Tamron DI macro lens, ISO 200, 1/60 sec.@f45. 19 August, 2009. Processed in Lightroom 3.2)


This entry was posted in Alberta, Entomology, Libellulidae, Odonata and tagged , .

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