Field Key to Adult Alaska Dragonflies

Dennis Paulson

Slater Museum of Natural History
University of Puget Sound, Tacoma, WA 98416

Revised Feb. 2004

This key has been prepared to provide identification in life of adults of the species of Odonata that occur in Alaska; it includes a few species not yet reported but likely to occur (indicated by an asterisk in the key). [This is a good place to note that the distribution of many Alaska species is poorly known, and many parts of the state have scarcely been surveyed for Odonata. A concerted effort to make local collections would be of great value.] Coloration is given much weight in the key, which would not be possible with dried specimens. Wing venation, the basis of many dragonfly keys, is ignored, although other structural attributes of the species are used when necessary. A 10x hand lens or other means of magnification is essential to see some of these characteristics, although a pair of binoculars can be just as effective if you reverse them. A small millimeter ruler is also necessary, as some species are distinguished by size.

An insect net is another essential, as the species will have to be learned by keying them out in the hand. Many details, although clearly visible at close range, cannot be seen at a distance, and they must be noted to proceed through the key. Once the species are learned in the hand, many of them will be easily recognizable in the field.

Each number in the key contains a pair of statements, each of which describes distinguishing characteristics. Read each statement before deciding to accept or reject either one, and note that some of them list more than one characteristic. Each one will lead either to a species name or another number. Measurements listed refer to total length unless otherwise indicated. When two are more species are listed together, they are difficult to distinguish in the field but differ by structural characteristics that are explained and illustrated in more technical books available in libraries such as The Dragonflies of British Columbia, by Robert Cannings and Kathleen Stuart, or The Odonata of Canada and Alaska, by Edmund Walker.

Males and females can be distinguished as follows. Males have a bump containing the accessory genitalia under the second abdominal segment; females lack this. Females typically have a broader abdomen than males, and female damselflies and darners (Aeshnidae) have a prominent ovipositor under the last segment. Male dragonflies have 3 appendages at the abdomen tip, male damselflies 4; females of both have only 2 such appendages. An important feature for identification in some families is the vulvar lamina under the 9th abdominal segment that supports the eggs about to be laid.

The key works for some teneral (just emerged) individuals, but at this age, color patterns are often insufficiently developed to be diagnostic. The definitive coloration of adults is acquired slowly with maturation, and individuals that are not yet mature may not be fully colored. Male dragonflies on territory at the water or individuals of either sex engaged in reproductive behavior will surely be mature. Some adults become pruinose, with a blue or whitish powdery bloom that covers parts of the body.

Familiarize yourself with basic dragonfly anatomy: head, thorax and abdomen, the latter with 10 segments. Anterior=front, posterior=rear, lateral=side, dorsal=top, ventral=bottom. Note the rectangular pterostigma near the tip of each wing.

First key the dragonfly in the Key to Families, then go to the appropriate family and key it to species.

Key to Families

  1. Slender; eyes farther apart than their own diameter; wings held together over abdomen (open in one family)...Zygoptera (damsels)...2
    Heavier-bodied; eyes closer together than their own diameter (touching in most species); wings always held wide open...Anisoptera (dragons)...3
  2. Wings held open (closed in hand, may be closed in tenerals); pterostigma long, equal to eye diameter...Lestidae
    Wings closed over abdomen (partially open in some individuals or in hand); length of pterostigma less than diameter of eye...Coenagrionidae
  3. Eyes separated...Gomphidae
    Eyes just touching or broadly contiguous...4
  4. Eyes just touching; large (65mm or more); black and yellow...Cordulegastridae
    Eyes broadly contiguous (if just touching, then length <65mm); varied colors...5
  5. Larger (>55mm); abdomen evenly spotted with blue and yellow, no markings on wings (except pterostigma)...Aeshnidae
    Smaller (if >55 mm, abdomen entirely black); abdomen patterned otherwise, wing markings in some...6
  6. Abdomen entirely black or black or brown with yellowish sides; eyes bright green or turquoise...Corduliidae
    Abdomen variously colored, if entirely black then eyes not green; if eyes green, then body blue or striped...Libellulidae

Lestidae (spreadwings)

  1. Thorax metallic green above...Lestes dryas (Emerald Spreadwing)
    Thorax bronzy to black above...2
  2. Rear of head partly pale, pterostigma light to medium brown, pale at ends; male superior appendages pale at base; from below, male inferior appendages curved outward toward tips...Lestes unguiculatus (Lyre-tipped Spreadwing)*
    Rear of head entirely dark, pterostigma usually uniformly dark; from below, male inferior appendages straight throughout...Lestes disjunctus (Northern Spreadwing)

Coenagrionidae (pond damsels)

  1. Abdomen black with blue tip, top of thorax entirely metallic green...Nehalennia irene (Sedge Sprite)
    Abdomen mostly blue, patterned with black, or mostly black (segment 8 may be pale), patterned with blue or brown and black; thorax not metallic green above...2
  2. Males--mostly blue; genitalia visible under 2nd abdominal segment; 4 appendages at tip of abdomen...3
    Females--mostly brown and black but may be almost as blue as males; no genitalia on 2nd abdominal segment; 2 appendages and ovipositor at tip of abdomen...5
  3. Middle abdominal segments mostly blue from above, black marking on second abdominal segment not U-shaped
    ...Enallagma boreale (Boreal Bluet), Enallagma annexum (Northern Bluet)
    [These two common species must be distinguished by structural characters.]
    Middle abdominal segments at least 50% black from above...4
  4. Thorax often with greenish tinge, no black markings beneath it; pale stripes on top of thorax undivided (divided in small proportion of individuals); no blue on abdominal segment 7...Coenagrion resolutum (Taiga Bluet)
    Thorax intense blue, with conspicuous black markings beneath; pale stripes on top of thorax divided (like exclamation marks); blue at abdomen tip extends onto segment 7...Coenagrion interrogatum (Subarctic Bluet)
  5. Segment 8 of abdomen mostly pale above...Enallagma boreale (Boreal Bluet), Enallagma annexum (Northern Bluet)
    [These two common species must be distinguished by structural characters.]
    Segment 8 of abdomen black above with conspicuous pale ring at end...6
  6. Abdominal segments 10 and 9 black above; no black markings under thorax...Coenagrion resolutum (Taiga Bluet)
    Abdominal segment 10 and half of 9 pale above; black markings under thorax...Coenagrion interrogatum (Subarctic Bluet)*

Gomphidae (clubtails)

It is remotely possible that a member of this family might occur in Alaska, the most likely species Ophiogomphus colubrinus (Boreal Snaketail) or Ophiogomphus severus (Pale Snaketail). Both have a greenish thorax, the former with a conspicuous stripe on the side and the latter without.

Aeshnidae (darners)

  1. Thorax entirely green...Anax junius (Common Green Darner)
    Thorax dark with pale stripes on sides...2
  2. Males (3 terminal appendages on abdomen)...3
    Females (2 terminal appendages and ovipositor on abdomen...10
  3. Superior appendages paddle-shaped in side view, becoming wider toward the rounded tip and ending in a ventral spine...4
    Superior appendages simple, not conspicuously wider toward the tip...5
  4. Abdominal spots larger, 25-33% length of each segment, conspicuous on 10th segment; no blue spots on underside of abdomen...Aeshna palmata (Paddle-tailed Darner)
    Abdominal spots small, 15-20% length of each segment, usually lacking on 10th segment; paired blue spots on underside of abdomen...Aeshna umbrosa (Shadow Darner)*
  5. Anterior lateral thoracic stripe narrow (<1 mm broad) and bent sharply twice in middle; small for family (<65 mm)...6
    Anterior lateral thoracic stripe straight or curved (if bent in middle, >1 mm broad); normal sized for family (>65 mm)...7
  6. Middle abdominal segments more black than blue above, anterior ends mostly black...Aeshna sitchensis (Zigzag Darner)
    Middle abdominal segments more blue than black above, anterior ends mostly blue...Aeshna septentrionalis (Azure Darner)
  7. Stripes on front of thorax reduced to fine streaks at midheight; lateral stripes of thorax narrow and straight...Aeshna interrupta (Variable Darner)
    Stripes on front of thorax broader, extending to upper edge, or represented there by isolated dots; lateral stripes varied...8
  8. First lateral thoracic stripe greatly constricted in middle; large species (>70 mm)...Aeshna eremita (Lake Darner)
    Lateral thoracic stripes straight or bent in middle; smaller species (<70 mm)...9
  9. Lateral thoracic stripes broad and straight, lacking a posterior offshoot from the upper...Aeshna juncea (Sedge Darner)
    Lateral thoracic stripes constricted at midlength, anterior one narrowed above the middle and with a slender posterior extension at the upper end...Aeshna subarctica (Subarctic Darner)
  10. Anterior lateral thoracic stripe narrow (<1 mm broad) and bent sharply twice in middle; small for family (<65 mm)...11
    Anterior lateral thoracic stripe straight or curved (if bent in middle, >1 mm broad); normal sized for family (>65 mm)...12
  11. From above, black marking just in front of eyes extends forward at each end, approaching the transverse black bar in front of it...Aeshna sitchensis (Zigzag Darner)
    Black marking just in front of eyes with no forward extensions
    ...Aeshna septentrionalis (Azure Darner)
  12. A bilobed plate covering the base of the ovipositor (underside of segment 9)...13
    No such plate covering the base of the ovipositor...14
  13. Valves of ovipositor flat below, in ventral view extending beyond tip of segment 9...Aeshna juncea (Sedge Darner)
    Valve of ovipositor ridged below, in ventral view extending just to tip of segment 9...Aeshna subarctica (Subarctic Darner)
  14. Underside of most abdominal segments with light basal spot on each side...Aeshna umbrosa (Shadow Darner)*
    Underside of abdomen entirely dark...15
  15. Thoracic stripes relatively broad, anterior one conspicuously indented at midlength; large (>70 mm)...Aeshna eremita (Lake Darner)
    Thoracic stripes straight, may be slightly sinuous; smaller (<70 mm)...16
  16. Lateral thoracic stripes typically broader than basal segment (femur) of hind leg; valves of ovipositor in side view very slightly sinuous--broadest at middle, then slightly narrowed, then slightly expanded at tip; difference seen only with adequate magnification...Aeshna palmata (Paddle-tailed Darner)
    Lateral thoracic stripes typically no broader than femur; valves of ovipositor straight in side view...Aeshna interrupta (Variable Darner)

Cordulegastridae (spiketails)

One species in extreme south, Cordulegaster dorsalis (Pacific Spiketail).

Corduliidae (emeralds)

  1. Male inferior appendage forked; female appendages 2mm or less in length...Cordulia shurtleffii (American Emerald)
    Male inferior appendage pointed; female appendages 3mm or more in length...2
  2. A very fine white ring at end of each abdominal segment...3
    No such rings (may be one on basal segment), abdomen entirely black or with yellow dots on side of each segment...4
  3. Male superior appendages viewed from above no wider than segment 10; female vulvar lamina (plate below segment 9) short, bilobed...Somatochlora albicincta (Ringed Emerald)
    Male superior appendages viewed from above expanded at base, distinctly wider than segment 10; female vulvar lamina long, conspicuously projecting below abdomen, not bilobed...Somatochlora hudsonica (Hudsonian Emerald)
  4. Males...5
    Females...12
  5. Superior appendages very hairy at tip, the hairs obscuring their shape...Somatochlora walshii (Brush-tipped Emerald)*
    Superior appendages not hairy, or with some hair but tip visible...6
  6. Tips of superior appendages slender, pointed and upcurved (viewed from side)...7
    Tips of superior appendages pointed but not upcurved, convergent from above...10
  7. From above, superior appendages essentially straight...Somatochlora minor (Ocellated Emerald)*
    From above, superior appendages sharply bent toward midline near the tip...8
  8. Hind wing with dark brown spot at extreme base...9
    Hind wing with no dark spot...Somatochlora sahlbergi (Treeline Emerald)
  9. Superior appendages viewed from above parallel to where they bend sharply ...Somatochlora septentrionalis (Muskeg Emerald)*
    Superior appendages converging toward middle, then diverging again before they bend...Somatochlora whitehousei (Whitehouse's Emerald)
  10. Hind wing with a dark brown spot at base...Somatochlora franklini (Delicate Emerald)
    Hind wing with at most a slight brown tinge at base...11
  11. Two yellow spots on each side of thorax...Somatochlora semicircularis (Mountain Emerald)
    Only one yellow spot on each side of thorax...Somatochlora kennedyi (Kennedy's Emerald)*
  12. Vulvar lamina (plate under segment 9) projecting downward at right angles to abdomen, very conspicuous...Somatochlora minor (Ocellated Emerald)*
    Vulvar lamina more or less parallel to abdomen, conspicuous or not...13
  13. Vulvar lamina about as long as or longer than segment 9...14
    Vulvar lamina distinctly shorter than segment 9...16
  14. Vulvar lamina dark, clearly longer than segment 9; two conspicuous yellow spots on sides of thorax, anterior one more elongate...Somatochlora walshii (Brush-tipped Emerald)*
    Vulvar lamina pale, no longer than segment 9; sides of thorax with one or no spots...15
  15. Terminal appendages about 2x as long as vulvar lamina; no yellow spots on sides of thorax...Somatochlora kennedyi (Kennedy's Emerald)*
    Terminal appendages about 1.5x as long as vulvar lamina; typically one anterior yellow spot on sides of thorax...Somatochlora franklini (Delicate Emerald)
  16. Hind wing with brown spot at extreme base...17
    Hind wing without brown spot...18
  17. Vulvar lamina compressed, not bilobed, projects downward in lateral view...Somatochlora whitehousei (Whitehouse's Emerald)
    Vulvar lamina flat, bilobed...Somatochlora septentrionalis (Muskeg Emerald)*
  18. Vulvar lamina compressed, not bilobed, projects slightly in lateral view ...Somatochlora semicircularis (Mountain Emerald)
    Vulvar lamina flat, notched or bilobed...Somatochlora sahlbergi (Treeline Emerald)

Libellulidae (skimmers)

  1. Hind wing with conspicuous dark spot at base, also small spot at midlength on each wing...Libellula quadrimaculata (Four-spotted Skimmer)
    Wings unspotted, may be suffused with yellow at base...2
  2. Body entirely black...Sympetrum danae (Black Meadowhawk)
    Body not entirely black...3
  3. Body mostly red or mostly yellow...4
    Body conspicuously patterned black and red or black and yellow...5
  4. Veins on fore edge of wing pale, contrasting with rest of wing; abdomen without conspicuous black markings...Sympetrum costiferum (Saffron-winged Meadowhawk)*
    All wing veins equally pale; abdomen with conspicuous black markings on side of each segment...Sympetrum internum (Cherry-faced Meadowhawk)
  5. Face brown or black...Sympetrum danae (Black Meadowhawk)
    Face white...6
  6. Males...7
    Females...11
  7. Abdomen with red or yellow spots above...8
    Abdomen entirely black, or with fine streak on middle segments...9
  8. Larger (>34 mm)...Leucorrhinia borealis (Boreal Whiteface)
    Smaller (<34 mm)...Leucorrhinia hudsonica (Hudsonian Whiteface)
  9. Larger (>30 mm)...10
    Smaller (<30 mm)...Leucorrhinia patricia (Canada Whiteface)
  10. Inferior appendage about half length of superiors...Leucorrhinia glacialis (Crimson-winged Whiteface)
    Inferior appendage about two-thirds length of superiors...Leucorrhinia proxima (Belted Whiteface)
  11. No red or yellow spot on top of segment 7...Leucorrhinia patricia (Canada Whiteface)
    Red or yellow spot on top of segment 7...12
  12. Red or yellow spot on segment 7 extends to end of segment...Leucorrhinia borealis (Boreal Whiteface)
    Red or yellow spot on segment 7 does not reach end of segment...13
  13. Smaller (<30 mm)...Leucorrhinia hudsonica (Hudsonian Whiteface)
    Larger (>30 mm)...Leucorrhinia glacialis (Crimson-ringed Whiteface), Leucorrhinia proxima (Belted Whiteface)
    [These two species can be distinguished only by wing venation; see published accounts.]