A piece of white schmutz was removed from the tip of the abdomen, enabling a clearer view of abdominal segment nine (S9). Look closely at the two photos featured in this post. Notice there are stubby mid-dorsal hooks (not cultriform) on abdominal segments four through eight (S4-S8).
The last photo shows a closer view of the anal pyramid. Notice the lateral caudal appendages (cerci) are less than half as long as the inferior appendages (paraprocts).
Soltesz, p. 43 – Key to the Species of the Genus Libellula
Field marks that match this specimen are highlighted in boldface green text.
1b. Dorsal hooks regularly present on segments 4 to 8. [2]
2b. Palpal setae 5 (sometimes 6 in cyanea). [5]
5a. Epiproct distinctly decurved at tip. [6]
6b. Length of last instar about 26mm; cerci less than half as long as paraprocts. [incesta]
Punch List
I need to look at the inside of the labium (face mask) in order to count palpal setae. The epiproct must be cleaned to see whether it is decurved. This exuvia was deformed as a result of emergence, so it’s impossible to make an accurate measurement of the length of the specimen. That said, the exuvia is more than 22.0 mm (0.9 in) long. (22 mm is the length of the last instar for L. cyanea.)
And of course, I need to annotate all of the images in this series of blog posts in order to illustrate the unfamiliar vocabulary that is used in virtually all dichotomous identification keys.
The following equipment was used to shoot the quick-and-dirty macro photographs featured in this post: Fujifilm X-T1 digital camera; Fujifilm MCEX-16 extension tube; and Fujinon XF80mm macro lens plus lens hood. The camera was set for both manual exposure and manual focus. That’s right, a switch on the camera body is used to set the type of focus. It’s a Fujifilm thing. Camera settings: focal length 80mm (120mm, 35mm equivalent); ISO 200; f/16; 1/180s.
This post features another photo of an odonate exuvia collected by Michael Powell during a photowalk with me on 01 June 2019 at Occoquan Regional Park, Fairfax County, Virginia USA. The photo is a one-off (not a composite image) showing the ventral view of the exuvia.
The following equipment was used to shoot the quick-and-dirty macro photograph featured in this post: Fujifilm X-T1 digital camera; Fujifilm MCEX-16 extension tube; and Fujinon XF80mm macro lens plus lens hood. The camera was set for both manual exposure and manual focus. That’s right, a switch on the camera body is used to set the type of focus. It’s a Fujifilm thing. Camera settings: focal length 80mm (120mm, 35mm equivalent); ISO 200; f/16; 1/180s.
Slaty Skimmer is a habitat generalist that can be found virtually anywhere there is water, such as a mid-size pond like Painted Turtle Pond.
This species is a true habitat generalist; only whitetails and pondhawks can be found in as many different habitat types. I’ve seen Slaties along river edges, sunny sections of woodland streams, ponds, lakes, swamps, old roads and flooded meadows. Dragonflies of summer, if you’re in any of these habitats June through September, you’re likely to come face to face with a Slaty Skimmer. Source Credit: Dragonflies of Northern Virginia, by Kevin Munroe.
The pointed- versus rounded eyes dichotomy is a somewhat subjective decision, but if you make the right choice then this field mark 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.
