How to Know the Butterflies

The Cornell classic that taught America to name what it saw: every eastern butterfly described from life, with its caterpillar, its food-plants, its habits — and how to pronounce its Latin.

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What a 1904 field guide knew about butterflies that most people still don’t.

John and Anna Comstock wrote this to be carried outdoors, and between the identification keys they let slip the strangest things they knew. Each of these links to the page it came from.

  1. Male butterflies wear perfume. Their wings carry scent-glands that open through modified scales, and the odour is thought to attract females — the exact counterpart, the Comstocks say, of bright plumage and birdsong in male birds.Read it: III. the Clothing of Butterflies
  2. The dark “brand” on a male skipper's wing is not a marking but an organ: a patch of tubular scales called androconia, each one the outlet of a scent-gland.Read it: Skippers with a Brand And Their Allies
  3. The male Blue Swallow-tail folds the inner margin of his hind wing over on itself — a pocket, with the scent-scales inside.Read it: The Blue Swallow-Tail
  4. The male Banded Hair-streak carries an oval patch of pale scent scales on each front wing, described as “his greatest attraction for his perfume-loving lady.”Read it: The Banded Hair-Streak (Thecla calanus Thec'la)
  5. That same butterfly has a taste for skunk-cabbage — “a plant which seems to have more friends among insects than among folks.”Read it: The Banded Hair-Streak (Thecla calanus Thec'la)
  6. The Cloudless Sulphur migrates in flocks southeast to northwest in spring and back again in autumn, and holds its line so stubbornly that observers record it flying over houses rather than around them.Read it: The Cloudless Sulphur (Callidryas eubule)
  7. One Georgia observer watched that same autumn migration for twenty-six consecutive years.Read it: The Cloudless Sulphur (Callidryas eubule)
  8. The Painted Lady is called the Cosmopolite for good reason: it has been found hundreds of miles out at sea, and migrates in flocks from one climate to another.Read it: The Cosmopolite (Vanessa cardui Va-nes'sa)
  9. Every adult butterfly has four wings, always. In many moths one sex is wingless — but this is true of no butterfly.Read it: II. the Structure of Butterflies
  10. Butterfly eggs are miniature architecture: shells ribbed and pitted, sometimes armed with spines, and frequently exquisitely coloured — rarely seen only because nobody looks closely enough.Read it: IV. the Metamorphoses of Butterflies
  11. The Polygonia look as though Nature had snipped their wing edges with scissors; and each hind wing carries, wrought in shining silver on the underside, an “initial” that identifies the species.Read it: Genus Polygonia
  12. Satyr caterpillars feed only at night, are sluggish by day, and stake everything on their colour and shape rather than on flight.Read it: The Carolinian Satyr (To the one who delves)
  13. In the Falcate Orange-Tip the sexes are reversed from the human arrangement: the female has the aesthetic taste and chooses the glowing colours for her spouse, while he, “not noticing dress,” is content that her wings lack the orange tips that make his beautiful.Read it: The Falcate Orange-Tip
  14. Butterfly scales come in a continuous gradation — hairlike on the body, broadening to the flat ribbed, toothed scale of the wing — and on the body and legs they work as armour.Read it: III. the Clothing of Butterflies
  15. The period collector's killing-bottle was charged with potassium cyanide sealed under plaster of Paris, left to dry in the shade, then corked and labelled Poison. Field natural history used to be genuinely dangerous.Read it: IV. the Metamorphoses of Butterflies: Poison
  16. A butterfly lives four separate lives — egg, caterpillar, chrysalis, adult — and the book insists on the word for it: a complete metamorphosis, mouth-parts and all rebuilt for sucking.Read it: General Account of Butterflies
  17. The single most drastic change in butterfly wings over evolutionary time was the loss of the main stem of the media vein, its branches annexed by the veins on either side — which is why wing venation identifies a family at a glance.Read it: II. the Structure of Butterflies: Lepidoptera
  18. Wood-nymphs, satyrs, graylings and meadow-browns are all one dull-coloured tribe, their wings “diversified rather than ornamented” with blackish eye-spots — built to hide rather than to outfly anything.Read it: The Carolinian Satyr (To the one who delves)
Rights & ReuseThe complete text of How to Know the Butterflies (1904) is in the public domain in the United States — like all works published before 1928 — and is free to read, download, quote, teach from, and reuse. This digital edition (its transcription, restored plates, and site design) is © 2026 PhotoOpAI, and any editorial commentary we add is clearly marked as ours; the underlying public-domain text carries no such restriction.