Pachydiplax longipennis

Pachydiplax longipennis

Family: Libellulidae

Blue Dasher (Pachydiplax longipennis) is a small, active skimmer of ponds, marshes, lake edges, vegetated ditches, and other still or slow waters. Mature males are especially distinctive, with a pale face, greenish eyes, a striped thorax, and a powder-blue abdomen ending in a dark tip. Females and immature males are more strongly patterned in yellow, brown, and black, often with reddish or two-toned eyes and lengthwise abdominal striping. In the field, Blue Dashers often give good photographic opportunities because they perch openly on grass stems, seedheads, twigs, and shoreline vegetation, making short flights and returning to watch for prey or rivals.

For representative images and visual context, see the page: Blue Dasher in the Gallery section.

Description

Pachydiplax longipennis is generally recognized by:

• Overall form: small to medium-sized perching skimmer; compact body with a relatively short abdomen
• Size: approximately 25–43 mm, or about 1–1.8 inches long
• Color pattern: mature males are powder-blue on the abdomen with a darker tip; females and immature males are yellowish to brown with dark striping
• Thorax: yellow to olive-yellow with dark brown or blackish shoulder and side stripes; striping is often visible in side views
• Abdomen: mature male abdomen is blue-pruinose through most of its length, with black terminal segments; females show dark lengthwise striping and pale/yellow markings
• Wings: mostly clear, often with amber or brownish patches near the bases, especially near the hindwings
• Wing posture: held open at rest, sometimes slightly cocked forward
• Eyes: mature males usually show greenish to blue-green eyes; females and immature males often show reddish-brown or red-over-blue-gray eyes
• Sex differences: mature males become blue and frosted-looking; females retain a more striped yellow/brown pattern, while immature males can resemble females before developing blue pruinosity

This is a dragonfly where age and sex matter. A bright blue male is usually straightforward, but females and immature males deserve closer inspection.

Habitat and Behavior

Typical habitats include:

• ponds, marshes, lake margins, boggy edges, slow streams, and vegetated ditches
• shoreline grasses, sedges, reeds, low shrubs, floating vegetation, and other open perches near still water

Behavioral notes:

• Perching: often perches openly on grasses, dry stems, seedheads, low twigs, or shoreline vegetation
• Flight: makes short, quick dashes from a perch, often returning to the same or a nearby lookout
• Territorial behavior: males defend small territories from exposed perches and may chase away other dragonflies, especially similarly colored males
• Seasonality: primarily a summer species in the Upper Midwest; most expected from late June into September, depending on location and season
• Activity: often locally common around sunny, vegetated still water

Blue Dashers are classic “sit-and-wait” hunters. They often use a perch as a lookout, launch after small flying insects, then settle again. This behavior can make them approachable for photography if you watch the perch pattern and move slowly.

Identification

Key features for field diagnosis:

• Size and build: small to medium skimmer with a short-looking abdomen and active perching behavior
• Thoracic pattern: yellow or olive-yellow thorax with dark shoulder and side stripes
• Abdominal markings: mature male with powder-blue abdomen and black tip; female and immature male with darker lengthwise abdominal striping
• Wing markings and posture: mostly clear wings with amber or brownish basal patches; wings held open, often slightly forward
• Eye placement and color: large dragonfly eyes meet on top of the head; mature males usually greenish, while females and immatures may show reddish or two-toned eyes
• Male appendages: black terminal appendages may be visible in sharp rear or side views
• Female traits: striped abdomen, paler terminal area, and a tube-type ovipositor may be visible in clear side views
• Behavioral cues: repeated return to exposed perches near still, vegetated water

A mature male Blue Dasher is usually identifiable from good photographs showing the pale face, striped thorax, blue abdomen, dark abdomen tip, and amber basal wing patches. Females and immature males are more easily confused with other small skimmers, so dorsal and side views are helpful. A single side view can often work if it shows the face, thorax stripes, wing bases, and abdomen pattern clearly.

For photographic identification, try to capture:

• side view showing thorax stripes
• dorsal or slightly angled view showing abdominal pattern
• clear view of the wing bases
• face and eye color when possible
• terminal abdomen if sex or maturity is uncertain

Similar Species

Use this section to distinguish Pachydiplax longipennis from likely lookalikes in Minnesota and the Upper Midwest.

• Eastern Pondhawk (Erythemis simplicicollis): Mature males are also blue, but they are generally stockier and lack the Blue Dasher’s white face, strongly striped yellow thorax, black abdomen tip, and amber basal wing patches. Females are green, which separates them readily from female Blue Dashers.

• Common Whitetail (Plathemis lydia): Males have a broad whitish abdomen and strong dark wing markings; females have a wider abdomen and bold wing spots. Blue Dasher is smaller, slimmer, and more delicate-looking, with a powder-blue male abdomen and striped thorax.

• Chalk-fronted Corporal (Ladona julia): Males can look pale or bluish at a glance, but they show a different thoracic pattern and more obvious dark basal wing patches. This species is also more associated with early-season northern or wooded wetland settings.

• Widow Skimmer (Libellula luctuosa): Much larger, with broad dark wing bands and white wing patches in mature males. Blue Dasher lacks the heavy wing banding and has a smaller, more compact build.

• Female and immature skimmers: Female Blue Dashers and immature males can be trickier. Look for the short abdomen, striped thorax, paired abdominal striping, amber basal wing patches, and perch-and-return behavior near vegetated still water.

Ecology and Notes

Blue Dasher is a widespread and familiar skimmer across much of North America and is fairly common in Minnesota where suitable habitat is present. It is usually associated with sunny, vegetated still water, including ponds, marshes, lake edges, slow streams, and ditches.

Males are territorial and often use repeated perch routes around breeding or feeding areas. Females may be less conspicuous, appearing around water for mating and egg-laying or hunting from nearby vegetation. Oviposition occurs in or around aquatic vegetation.

Useful field notes:

• Blue Dashers often return to favorite perches, making them good subjects for patient macro photography.
• Mature males develop a powder-blue pruinosity that can obscure some underlying markings.
• Immature males can resemble females before turning blue.
• Females may become somewhat bluish with age but usually retain more patterned markings than mature males.
• Hot individuals may raise the abdomen in an obelisk-like posture to manage sun exposure.
• Wing wear, faded color, and pruinosity can make older individuals look different from fresh adults.

Identification from photographs is usually reliable for mature males. Females and immatures are best identified with multiple views, especially side and dorsal images showing thorax stripes, wing bases, abdomen pattern, and terminal segments.

References

• Odonata Central https://www.odonatacentral.org/

• iNaturalist taxon page https://www.inaturalist.org/taxa/59774

• BugGuide: Species Pachydiplax longipennis - Blue Dasher https://bugguide.net/node/view/598

• Minnesota Dragonfly: Blue Dasher https://mndragonfly.info/html/skimmers/bluedasher.html

• MinnesotaSeasons: blue dasher https://www.minnesotaseasons.com/Insects/blue_dasher.html

• Wisconsin Odonata Survey: Pachydiplax longipennis https://wiatri.net/inventory/odonata/SpeciesAccounts/SpeciesDetail.cfm?TaxaID=157

• Paulson, Dennis. Dragonflies and Damselflies of the East Princeton University Press.