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Lateral view of a Male Baetis (Baetidae) (Blue-Winged Olive) Mayfly Dun from Mystery Creek #43 in New York
Blue-winged Olives

Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.

27" brown trout, my largest ever. It was the sub-dominant fish in its pool. After this, I hooked the bigger one, but I couldn't land it.
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Identification: Key to Orders of Aquatic Insect Nymphs

Identification: Key to Orders of Aquatic Insect Nymphs

Option 1Option 2
Chewing mouthparts, with mandibles distinct
Figure from this Isoperla adult.
Sucking mouthparts, united in a jointed beak with mandibles concealed
Remaining orders: Ephemeroptera, Odonata-Anisoptera, Odonata-Zygoptera, Orthoptera, and Plecoptera
5 Example Specimens
Go to Couplet 2 Hemiptera
The current couplet is highlighted with darker colors and a icon, and couplets leading to this point have a icon.
Couplet 1

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Couplet 1 (You are here)
Leads to Couplet 2:
  • Chewing mouthparts, with mandibles distinct
Couplet 2
Leads to Hemiptera:
  • Sucking mouthparts, united in a jointed beak with mandibles concealed
Leads to Orthoptera:
  • Hind legs suitable for jumping, with hind femora greatly enlarged
  • Abdomen with short tails
  • Found in moist places and only temporarily in water
Leads to Couplet 3:
  • Hind legs suited for crawling, with hind femora similar in size to front and middle femora, not greatly enlarged
  • Abdomen with or without conspicuous tails
  • Usually submerged and truly aquatic
Couplet 3
Leads to Couplet 5:
  • Labium (lower lip) mask-like, extendable into a scoop-like structure longer than head
Couplet 5
Leads to Couplet 4:
  • Labium normal, smaller than head, not large and mask-like
Couplet 4
Leads to Ephemeroptera:
  • Tarsi almost always with one claw
  • Usually 3 tails, but sometimes 2
  • Plate-like, filamentous, or feathery gills located on sides of abdomen, often present on most middle abdominal segments
Leads to Plecoptera:
  • Tarsi with 2 claws
  • Always 2 tails
  • Finger-like or feathery gills present, but sometimes inconspicuous at base of mouthparts, head, legs, first few abdominal segments, or last abdominal segment
Leads to Odonata-Zygoptera:
  • Body slender, with head wider than thorax and abdomen
  • 3 long, caudal tracheal gills at the tip of the abdomen resemble paddle-like tails
Leads to Odonata-Anisoptera:
  • Body stout, with head usually narrower than thorax and abdomen
  • 5 short, stiff, pointed appendages at the tip of the abdomen

Start a Discussion of this Couplet


Orders excluded
These orders of Insecta are not included in this key: Trichoptera, Diptera, Coleoptera, Megaloptera, Lepidoptera, Hymenoptera, Neuroptera, Psocodea
Description of this key
This key only covers insect orders whose juvenile stages are typically referred to as nymphs. Invertebrates that have larvae instead are not included.
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