SOME CATERPILLARS OF ONTARIO, CANADA
photos taken by Bea Laporte and identified mostly by Butterflies and Moths of North America's website at BAMONA or with help from Peterson's Field Guide to Moths of Northeastern North America
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A caterpillar (or larva) is the stage between the egg and the adult during the life cycle of a butterfly or moth (from the insect family: Lepidoptera). Every caterpillar species have specific plants they like to feed on called the "host plant", so knowing the name of the host plant that the caterpillar is on can often help with identifying the critter. Also, caterpillars have many stages called instars and can look very different from when they hatch until when they go into a pupa.
Yellow-striped Armyworm MOTH
Yellow-striped Armyworm MOTH
Armyworm
European Yellow Underwing MOTH
Orange-humped Mapleworm MOTH
Red-humped Oakworm MOTH
Zebra Caterpillar 
Brown Hooded Owlet MOTH
Dusky Hooded Owlet MOTH
Bronzed Cutworm MOTH
Common Eupithecia MOTH
Goldenrod Hooded Owlet MOTH
Speckled Green Fruitworm MOTH
Dowdy Pinion
Maple Prominent
Red-lined Panopoda MOTH
Common Looper
Hitched Arches
Giant Swallowtail
Black Swallowtail
Viceroy
Variable Oakleaf Caterpillar MOTH
Mottled Prominent
Polyphemus
Painted Lichen
Leconte's Haploa
Arge Tiger
Purple-backed Cabbageworm MOTH
Monarch
Hermit Sphinx
Great Ash Sphinx
Hummingbird Clearwing MOTH
Virginia Creeper Sphinx MOTH
Laurel Sphinx
Black-rimmed Prominent MOTH
Banded Hairstreak BUTTERFLY
Striped Hairstreak BUTTERFLY
Crowned Slug
Spiny Oak-slug
Eastern Tent Caterpiller MOTH
Forest Tent Caterpiller MOTH
Virginian Tiger
Yellow Bear
Delicate Cycnia
Fall Webworm
Eight-spotted Forester MOTH
Spiny Looper MOTH
Yellow-necked Caterpillar MOTH
Purple-lined Sallow MOTH
Purple-lined Sallow MOTH
Gray Hooded Owlet MOTH
Banded Tussock or Pale Tiger MOTH
Spotted Tussock
Hickory Tussock
Milkweed Tussock
Definite-marked Tussock MOTH
White-marked Tussock
Ochre Dagger
Cottonwood Dagger
American Dagger
Henry's Marsh
Salt Marsh
Impressed Dagger
Gypsy
Banded Woolybear or Isabella Tiger MOTH
Giant Leopard
Virginia Ctenucha
Question Mark
Great Spangled Fritillary BUTTERFLY
Mourning Cloak
Red Admiral
IOBelow are some larvae that look like caterpillars but do not turn into moths or butterflies. So, how can you tell them apart? Caterpillars may have up to five pairs of abdominal prolegs and never more but Sawfly larvae always have six or more pairs. Prolegs are those stubby and fleshy, unsegmented legs, found in pairs on the underneath side of the larva. Beetle larva only have three true legs and no prolegs.
Oak SAWFLY
Elm SAWFLY