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For the United States & Canada
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Order Lepidoptera - Butterflies and Moths

pandemis limitata? - Pandemis limitata Acossus centerensis? - female Platynota idaeusalis - male Eupithecia miserulata - Common Eupithecia  - Eupithecia miserulata Noctuidae? - Macrochilo louisiana - male Web worms - Hyphantria cunea Celiptera valina Lépidoptère - Acossus centerensis - male
Show images of: caterpillars · adults · both
Kingdom Animalia (Animals)
Phylum Arthropoda (Arthropods)
Subphylum Hexapoda (Hexapods)
Class Insecta (Insects)
Order Lepidoptera (Butterflies and Moths)
Other Common Names
larvae commonly called caterpillars
pupal case, when covered in silk, commonly called a cocoon
the pupa of a butterfly is typically called a chrysalis
Spanish: polilla (referring mostly to clothes moth), mariposa de la noche, mariposa nocturna (night butterfly), paloma (literally, dove)
French: mite (referring mostly to clothes moth), papillon de nuit (night butterfly, as in Spanish)
Synonyms and other taxonomic changes
As of 2016, BugGuide follows with caution the Pohl, et al. 2016 provisional checklist (1) which is the updated version of the checklist at MPG. This is a working paper and not yet peer reviewed; however, it is based on peer reviewed work. It can be viewed or downloaded here.
Notes prior to 2016: BugGuide currently follows the classification found at ZooKeys. An updated list can be found in the "Latin Name Index" at MPG here. (Click on "Download current MPG checklist file" near the middle of the page.)
See discussion on forum here which is an update to the discussion here for more information.
Markku Savela's Lepidoptera site is invaluable for synonyms, links to original literature, distributions south of the border, and numbers of spp. Search by genus or genus species.
For butterflies, see: A Catalogue of the Butterflies of the United States and Canada - Jonathan P. Pelham
Explanation of Names
Lepidoptera means "scale wing", from Greek: lepis (λεπις / genitive form λεπιδος)- "scale" + ptera (πτερα)- "wing"
The related word "motte" in German shows that "moth" was inherited from the ancestral language that gave rise to both German and English. The Old English form was "moþþe" ("moththe" after converting the Old English letter thorn). The original meaning is unclear; mothhthe is perhaps related to maggot (older Germanic forms mado, made) and/or midge (Patridge, 1958; Wiktionary--moth; Wikipedia--Moth-etymology). It seems likely that the original meaning referred to moth caterpillars, and it may have referred, in particular, to human commensals such as Tineola bisselliella, the Webbing Clothes Moth.
For a tab-delimited text file list of all species level pages currently shown at BugGuide, see Article 1401565. The list can be copied and pasted to an empty spreadsheet.

89 families and 12,766+ species in North America (1), although there are many undescribed species (mostly micromoths).(Lepidoptera Bar Code of Life)
At least a couple of hundreds are introduced species. Bugguide lists 220 non-natives as of 2/1/2022
Over 150,000 described species worldwide, of which fewer than 20,000 are butterflies.(2) Many tens of thousands are undescribed.
Wingspan of North American species ranges from about 2-3 mm in the tiniest micromoths, to more than 150 mm in the largest silk, sphinx, and owlet moths; some tropical species have wingspans of more than 250 mm (see Largest Lepidopteran Wing Span)
Adults (imagos) have four membranous wings (rarely wingless); hindwings are usually smaller than forewings, both largely or entirely covered with scales. Adult mouthparts adapted for sucking, the proboscis is usually in the form of a coiled tube (adults of some species lack mouthparts and do not feed as adults). Images showing the characteristics of the order Lepidoptera:

Common practice is to divide the Lepidoptera into two (or three) groups, though this is not, strictly speaking, a taxonomic division. (Butterflies and skippers are a monophyletic group within the Lepidoptera [Papilionoidea], but "moths" are a paraphyletic group.)
Moths usually have feathery antennae and most are active at night. They generally rest with their wings open, either flat or "tented" over the body. Rarely, the wings are held together vertically above the body as with butterflies.

When they pupate above ground they generally form a protective cocoon around the pupa. This is made of silk, often combined with other natural materials such as leaves or their own body hair. The caterpillars of many species dig into the ground to pupate.
Butterflies have thin antennae with "knobs" on the end and are generally active during the day. They rest with their wings closed above their bodies, and make a naked pupa also known as a chrysalis.
Skippers are a separate group of butterflies, with many distinctive features. They are (mostly) day-flying, have knobbed antennae, and rest with wings folded or spread, depending on the group.

Date/time-of-year and foodplant (for caterpillars) are sometimes helpful in determining the species.

Larvae (caterpillars) have a hardened head capsule and a fleshy body composed of a thorax bearing three pairs of legs, and an elongated cylindrical abdomen bearing from zero to five pairs of prolegs (short fleshy ventral projections used for clinging or walking). The body may be either uniformly colored or patterned with stripes, bands, or spots; the surface may be smooth, or may be sparsely or densely covered with short or long hairs, tufts of hair, spines, knobs, or other features.

For a start on identification of moth families, see:

Some info pages have guides to identification; refer to this list of them and subscribe to the page for email updates when new guides are added.

      Salticid Mimics             Pine-feeding           Tan with Streaks            Mostly Black          Silver with Orange   White with Black Spots

Wing terminology

Note: this is not a comprehensive guide to all moth species in the United States and Canada. The images shown here merely serve to provide a general idea as to the "shape" and diversity of the 32 moth superfamilies in our area. Please post unknown moth images at "ID Request" if the superfamily is unknown.

Superfamily Adeloidea: Fairy Moths and kin

Superfamily Alucitoidea: Many-plume Moths

Superfamily Bombycoidea: Silkworm, Sphinx, and Royal Moths

Superfamily Choreutoidea: Metalmark Moths

Superfamily Copromorphoidea: Fruitworm Moths

Superfamily Cossoidea: Carpenter and Leopard Moths

Superfamily Drepanoidea: Hooktip and False Owlet Moths

Superfamily Epermenioidea: Fringe-tufted Moths

Superfamily Eriocranioidea: Eriocraniid Moths

Superfamily Gelechioidea: Twirler Moths and kin

Superfamily Geometroidea: Geometrid (Inchworm) and Swallowtail Moths

Superfamily Gracillarioidea: Ribbed Cocoon-maker and Leaf Blotch Miner Moths

Superfamily Lasiocampoidea: Tent Caterpillar and Lappet Moths

Superfamily Micropterigoidea: Mandibulate Archaic Moths

Superfamily Mimallonoidea: Sack-bearer Moths

Superfamily Neopseustoidea: Archaic Sun Moths

Superfamily Nepticuloidea: Pygmy Leaf-mining Moths

Superfamily Noctuoidea: Owlet Moths and kin

Superfamily Papilionoidea: Butterflies and Skippers

Superfamily Pyraloidea: Pyralid and Crambid Snout Moths

Superfamily Schreckensteinioidea: Bristle-legged Moths

Superfamily Sesioidea: Clearwing Moths

Superfamily Thyridoidea: Window-winged Moths

Superfamily Tineoidea: Tubeworm, Bagworm, and Clothes Moths

Superfamily Tischerioidea: Trumpet Leafminer Moths

Superfamily Tortricoidea: Tortricid Moths

Superfamily Urodoidea: False Burnet Moths

Superfamily Yponomeutoidea: Ermine Moths and kin

Superfamily Zygaenoidea: Flannel, Slug Caterpillar, Leaf Skeletonizer Moths and kin
Please report significant date, location and/or species records to your local LepSoc Zone Coordinator
Caterpillars are found in the habitat where their food is. Adults tend to be in the general area of their larval foodplants,
Larvae may be found anywhere on their host plant, from underground on or inside the roots, to the highest leaves of tall trees; a few species are aquatic, developing on or in standing or running water
Adults are generally found near the larval host plant, but many migrate over great distances. Many species are attracted to artificial light. Moths are essentially a group of nocturnal insects but butterflies and some moths are diurnal; see Internet Reference (TT).
Caterpillars are active when their hostplants are plentiful, which is often spring and summer. Adults are usually seen when there are flowers to feed on. Because they over-winter, though, there are individuals of some species to be found any time of the year, even in cold climates. Seasonal patterns are usually species-specific, and some species can only be distinguished in the field by their season of activity. Species considered household pests may be active all year indoors.
Most adult moths and butterflies use their coiled mouthparts to suck nectar from flowers of a great variety of woody and herbaceous plants. In the process they may transfer pollen from one flower to another, and many plants depend on moths or butterflies for pollination. Secondary foods include sugary secretions (honeydew) from insects, juices of decaying fruit, tree sap, and manure liquids; adult moths in several families have either no mouthparts or non-functional mouthparts, and therefore do not feed as adults.
Depending on species, larvae may feed on all parts of herbaceous plants, roots/twigs/stems/leaves of trees and shrubs, fungi, lichens, dead or decaying plant material, stored food products, fabrics made of cotton or wool, or generally any organic material; many species are very host-specific, and can be identified by the plant they are feeding on; larvae of a few species are known to eat other caterpillars, and a few other species eat soft-bodied insects such as aphids. See: Carnivorous Lepidoptera
Life Cycle
These insects undergo complete metamorphosis; that is, each individual goes through four stages: egg, larva (the caterpillar), pupa (chrysalis), and adult.
The larval stage does most of the eating and growing, with the adults often staying alive just long enough to mate and lay eggs.
Many species have one generation per year; others may have from two to several generations; a few species take more than one year to develop. Depending on species, moths may overwinter as an egg, larva, pupa, or adult. Adult lifespan ranges from as short as a few days (in ghost moths) up to several months in species that overwinter as an adult.
Butterflies can have 5-6 larval stages.(4)
Contrary to popular belief, butterflies and moths will not die if the scales are rubbed off their wings.
Butterflies evolved from within the moths; thus, butterflies are a group of day-flying moths.
See Also
Trichoptera (caddisflies) tend to have hairs rather than scales on their wings; no coiled proboscis
larvae of sawflies (Hymenoptera)--often mistaken for caterpillars but have more than five pairs of prolegs, whereas caterpillars always have five or fewer pairs.
larvae of some lady beetles--have waxy white tufts may be mistaken for hairy caterpillars, but have no prolegs and always consume living insects.
various other insects are sometimes mistaken for small moths--see moth flies, whiteflies, pleasing lacewings, and derbid planthoppers in the genus Otiocerus
Print References
Covell, Peterson Field Guides: Eastern Moths (5), Field Guide to Moths of Eastern North America (reprint) (6)
Himmelman, Discovering Moths: Nighttime Jewels in Your Own Backyard (7)
McFarland, N. 1964. Notes on collecting, rearing, and preserving larvae of macrolepidoptera. Jl. Lep. Soc. 18(4): 201-210; additional notes, 1965, vol. 19(4): 233-236
Miller, J. C. & P. C. Hammond 2003. Lepidoptera of the Pacific Northwest: caterpillars and adults. FHTET-03-11: 1-323 (PDF)(8)
Patridge, 1958. Origins: A short Etymological Dictionary of Modern English. New York: MacMillan, 972 pp.
Internet References
Moth Photographers Group - Main Menu (covers United States and Canada) (Bob Patterson [Webmaster], hosted by Mississippi State U.)
Moth Photographers Group Plates - several thousand pinned and live adult photos of all types of moths by many individuals and a few organizations
Butterflies of America - Intro (covers all of North and South America)
Butterflies and Moths of North America - Intro (covers United States only)
Butterflies and Moths of Canada (CBIF) - classification, distribution, and identified pinned adult photos of more than 2,000 species of macromoths occurring in Canada (J.T. Troubridge and J.D. Lafontaine, Canadian Biodiversity Information Facility)
Lepidoptera Barcode of Life (covers the world)
Caterpillars of Massachusetts (photographs only)
Tree of Life (covers the world, but only as a taxonomic tree with a few sample images)
Moth Identification. North Dakota State U.
Moths of Ottawa area - live adult photos of about 500 species of mostly macromoths (Lynn Scott, Ontario)
North Dakota State University - Glossary with images showing wing venations
NIC.FUNET.FI - an invaluable site for synonyms, links to original descriptions, literature, and other information.
Pacific Northwest Moths - a "comprehensive source of information about more than 1,200 species of moths" found in the PNW