The pointed- versus rounded eyes dichotomy is a somewhat subjective decision, but if you make the right choice then this marker can be used to narrow the range of possible Libellulidae genera.
Exuviae from three genera of Libellulidae have pointed eyes: Libellula (18 species); Orthemis (3 species); and Plathemis (2 species). Slaty Skimmer (Libellula incesta) is one of 18 species in the genus Libellula.
Exuviae from all other genera of Libellulidae have rounded eyes.
Female Slaty Skimmers have a pair of flanges beneath their eighth abdominal segment (S8) that are used to scoop water when laying eggs (oviposition), hence the family name “Skimmer.”
Odonates (dragonflies and damselflies) are aquatic insects that spend most of their life as larvae that live in water; this stage of their life cycle can last from a few months to a few years, depending upon the species. Finally, they emerge from the water and metamorphose into adults in order to reproduce; their offspring return to the water and the cycle begins again.
All dragonflies and damselflies have a 10-segmented abdomen, numbered from front to back: male dragonfly secondary genitalia, called hamules, are located in segments two and three (S2 and S3); female genitalia in segment eight (S8). Dragonflies form the mating wheel in order for their genitalia to connect during copulation.
These two males were rivals, competing for one of two perches overlooking a wetland pool. I was amused by the smaller Blue Dasher’s aggressive behavior as he buzzed the larger Slaty Skimmer repeatedly, trying to recapture the prized perch he occupied before the Slaty showed up.
It is uncommon to see the broad-winged skimmers from the genus Tramea perching. Dragonflies are classified as either “fliers” or “perchers,” based upon their feeding habits. Black Saddlebags are fliers.
Black Saddlebags is one of at least five major species of dragonflies known to be migratory in North America. Broad hindwings is an adaptation that enables Black Saddlebags to glide easily when flying. Dragonflies expend less energy when gliding, an aide to long-distance migration. According to the axiom in biology/morphology, form follows function.
Slaty Skimmer dragonflies (Libellula incesta), such as the mature male shown below, look somewhat similar to Black Saddlebags. Slaty Skimmers are “perchers.” Slaty Skimmers aren’t migratory; notice their hindwings are narrower than Black Saddlebags.
Slaty Skimmer (Libellula incesta) is a member of the Skimmer Family of dragonflies. Females lay eggs (oviposition) by skimming the water surface repeatedly, hence the family name “Skimmer“; two flanges beneath their eighth abdominal segment (S8) scoop water that is used to flick fertilized eggs toward shore, as illustrated in the following annotated image. Remember that all dragonflies and damselflies have a 10-segmented abdomen, numbered from front to back.
10 JUN 2015 | Huntley Meadows Park | Slaty Skimmer (mature female)
The following movie shows the same female laying eggs in a large pool of water downstream from the central wetland area at Huntley Meadows Park on 10 June 2015.
Tech Tip: The preceding movie looks better viewed in full-screen mode.
Slaty Skimmers display sexual dimorphism. Although mature males and females look different, immature males and females look similar. Terminal appendages may be used to differentiate immature males from females.
06 JUN 2015 | Huntley Meadows Park | Slaty Skimmer (female)
Female dragonflies have a pair of cerci (superior appendages) that have little or no function. (See a full-size version of the following image, without annotation.)
06 JUN 2015 | Huntley Meadows Park | Slaty Skimmer (female)
Look closely at the full-size version of the preceding annotated image. Female Slaty Skimmers have a pair of flanges beneath their eighth abdominal segment (S8) that are used to scoop water when laying eggs (oviposition), hence the family name “Skimmer.” Remember that all dragonflies and damselflies have a 10-segmented abdomen, numbered from front to back.
Immature male Slaty Skimmers and immature/adult female Slaty Skimmers are nearly identical in appearance except for their terminal appendages. (See a full-size version of the following image, without annotation.)
Male dragonflies have three terminal appendages, collectively called “claspers,” that are used to grab and hold female dragonflies during mating: an upper pair of cerci (“superior appendages”) and a lower unpaired epiproct (“inferior appendage”). (See a full-size version of the following image, without annotation.)
06 JUN 2015 | Huntley Meadows Park | Slaty Skimmer (young male)
This individual is a young male, as indicated by the blue-black partial pruinescence covering his body. He has a slightly malformed wing that is more noticeable in the preceding side view and less noticeable in the following dorsal view.
06 JUN 2015 | Huntley Meadows Park | Slaty Skimmer (young male)
Black pruinescence that completely covers the body of following mature male Slaty Skimmer makes it look quite different from the immature male (shown above), other than its terminal appendages.
Look closely at the full-size version of the following annotated image. Female Great Blue Skimmers have a pair of flanges beneath their eighth abdominal segment (S8) that are used to scoop water when laying eggs (oviposition), hence the family name “Skimmer.” Remember that all dragonflies and damselflies have a 10-segmented abdomen, numbered from front to back.
Immature Great Blue Skimmer dragonflies and immature Slaty Skimmer dragonflies (Libellula incesta) — including both females and males — look very similar. In my opinion, the best field marker for differentiating the two species is femur coloration: Great Blue Skimmer femora are mostly tan; Slaty Skimmer femora are mostly black.
The following female Slaty Skimmer was spotted along the “Hike-Bike Trail” at Huntley Meadows Park. Contrast the difference in coloration of the Slaty Skimmer femurs (below) with the Great Blue Skimmer femurs (above).
