Insects & spiders
What caterpillar is this?
The plant it was sitting on is the strongest clue you have. Most caterpillars eat a short list of hosts, so "green, on a tomato plant" is a far better query than "green caterpillar". Filter by host first, then by whether it is smooth, furry or spiny — and check the sting column before you pick it up.
Some of these sting. Puss, saddleback, io, buck moth and spiny oak slug caterpillars carry venomous spines that break off in skin and cause burning pain, welts and occasionally a systemic reaction. Never handle a caterpillar with spines, tufts or dense fur. If you are stung, strip the spines off with tape before washing, then ice; get medical help for chest pain, difficulty breathing, or if the person has a history of severe reactions.
Narrow it down
Showing all 34 caterpillars
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Monarch
Danaus plexippus
Bold bands of yellow, white and black around a smooth body, with two pairs of soft black filaments — one behind the head, one near the tail. Only ever on milkweed.
In the record 799,895 georeferenced records · half of them Jul–Sep · most distinctive in January · mostly from the United States check on GBIF
Common caterpillar types -
Black swallowtail
Papilio polyxenes
Green with black bands and a row of yellow-orange dots on each band, found on parsley, dill, fennel or carrot tops. Poke it gently and an orange forked organ pops out of the head, smelling sour.
In the record 118,300 georeferenced records · half of them Jun–Aug · most distinctive in February · mostly from the United States check on GBIF
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Tomato hornworm
Manduca quinquemaculata
Enormous, plump, bright green, with eight white V-shaped marks pointing forward along each side and a black or dark-blue horn on the rear.
In the record 5,963 georeferenced records · half of them Jun–Aug · most distinctive in October · mostly from the United States check on GBIF
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Tobacco hornworm
Manduca sexta
Seven straight white diagonal stripes along each side and a curved red horn. This is the hornworm most often found on tomatoes despite the name.
In the record 21,557 georeferenced records · half of them Jul–Aug · most distinctive in October · mostly from the United States check on GBIF
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Woolly bear
Pyrrharctia isabella
Dense stiff bristles, black at both ends with a rust-brown band in the middle, hurrying across a road or path in September and October looking for somewhere to overwinter.
In the record 73,490 georeferenced records · half of them Aug–Oct · most distinctive in October · mostly from the United States check on GBIF
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Yellow woolly bear
Spilosoma virginica
A uniformly shaggy caterpillar in pale yellow, cream or occasionally rust, with no black ends. The long soft hairs can irritate sensitive skin, unlike the true woolly bear.
In the record 39,530 georeferenced records · half of them Jun–Aug · most distinctive in October · mostly from the United States check on GBIF
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Eastern tent caterpillar
Malacosoma americanum
A continuous white stripe down the centre of the back, blue and orange dashes along the sides, and a dense silk tent built in the fork of a wild cherry or apple branch in April and May.
In the record 46,809 georeferenced records · half of them Apr–May · most distinctive in April · mostly from the United States check on GBIF
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Forest tent caterpillar
Malacosoma disstria
A row of white keyhole or footprint shapes down the back instead of a continuous line, and it builds no tent — it spins a silk mat on the trunk and rests there in a mass.
In the record 29,306 georeferenced records · half of them Apr–Jun · most distinctive in April · mostly from the United States check on GBIF
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Fall webworm
Hyphantria cunea
Pale hairy caterpillars living inside a loose grey web that encloses the leaves at the very tip of a branch, expanding through August and September. Ugly, harmless to the tree.
In the record 50,172 georeferenced records · half of them Jun–Aug · most distinctive in November · mostly from the United States check on GBIF
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Spongy moth
Lymantria dispar
Five pairs of blue dots followed by six pairs of red dots down the back — a colour sequence nothing else has — with long straggling hairs. Formerly called the gypsy moth.
In the record 146,176 georeferenced records · half of them Jun–Jul · most distinctive in June · mostly from the Netherlands check on GBIF
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White-marked tussock moth
Handle with careOrgyia leucostigma
A bright red head, four short cream toothbrush tufts on the back, and two long black hair pencils pointing forward with one pointing back. Unmistakable once seen.
In the record 24,554 georeferenced records · half of them Jun–Aug · most distinctive in October · mostly from the United States check on GBIF
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Hickory tussock moth
Handle with careLophocampa caryae
White and fluffy with a row of black tufts down the back and four long black pencils at each end, found on hickory, walnut and ash — and very often crossing a sidewalk in August.
In the record 41,768 georeferenced records · half of them Aug–Sep · most distinctive in October · mostly from the United States check on GBIF
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Milkweed tussock moth
Euchaetes egle
Clusters of caterpillars covered in dense tufts of black, orange and white hair, stripping a milkweed leaf together late in the season after the monarchs have gone.
In the record 31,712 georeferenced records · half of them Aug–Aug · most distinctive in August · mostly from the United States check on GBIF
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Puss caterpillar
Can injure youMegalopyge opercularis
Looks like a small toupee or a tuft of cotton wool, tan to grey, with a pointed tail of longer hair. The venomous spines are hidden entirely under the soft outer fur.
In the record 9,349 georeferenced records · half of them Apr–Jul · most distinctive in November · mostly from the United States check on GBIF
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Saddleback caterpillar
Can injure youAcharia stimulea
A brown slug-like body with a bright green blanket across the middle carrying a purple-brown oval "saddle", and four stout horned spine clusters at the corners.
In the record 6,702 georeferenced records · half of them Jul–Aug · most distinctive in September · mostly from the United States check on GBIF
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Io moth caterpillar
Can injure youAutomeris io
Pale green with a red-and-white stripe along each side and dense clusters of branched, bright green venomous spines over the whole body.
In the record 24,812 georeferenced records · half of them May–Jul · most distinctive in December · mostly from the United States check on GBIF
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Buck moth caterpillar
Can injure youHemileuca maia
Dark purple-black speckled with white dots and armed with rosettes of branched, hollow, cream-tipped spines. Feeds in groups on oak, often dropping on people below.
In the record 1,061 georeferenced records · half of them Sep–Oct · most distinctive in October · mostly from the United States check on GBIF
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Spiny oak slug
Can injure youEuclea delphinii
Flat, oval and slug-shaped with no visible head, in green or yellow, edged with paired spiny horns and usually carrying four dark spots on the back.
In the record 8,443 georeferenced records · half of them Jun–Jul · most distinctive in June · mostly from the United States check on GBIF
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Luna moth caterpillar
Actias luna
Fat, bright translucent green with a faint yellow line along each side and small orange knobs down the back, each with a short bristle. It clicks its mandibles if disturbed.
In the record 47,535 georeferenced records · half of them May–Jul · most distinctive in March · mostly from the United States check on GBIF
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Cecropia moth caterpillar
Hyalophora cecropia
The largest caterpillar in North America: a thumb-thick blue-green body studded with blue, yellow and red knobs carrying black spines. Alarming and completely harmless.
In the record 13,844 georeferenced records · half of them Apr–Jun · most distinctive in February · mostly from the United States check on GBIF
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Polyphemus moth caterpillar
Antheraea polyphemus
Bright apple-green with a diagonal yellow line running back from each pair of legs and small red-and-silver knobs. Body is strongly ridged into fat segments.
In the record 53,407 georeferenced records · half of them May–Jul · most distinctive in February · mostly from the United States check on GBIF
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Mourning cloak caterpillar
Nymphalis antiopa
Velvety black speckled with white, a row of eight red-orange spots down the back and branched black spines. Feeds in a dense group that strips a whole branch at once.
In the record 247,233 georeferenced records · half of them Apr–Jun · most distinctive in April · mostly from Finland check on GBIF
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Great spangled fritillary caterpillar
Speyeria cybele
Velvety black with orange-based branched spines, feeding only on violets and only at night — which is why it is usually found on the ground rather than on a plant.
In the record 62,911 georeferenced records · half of them Jun–Jul · most distinctive in June · mostly from the United States check on GBIF
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Cabbage looper
Trichoplusia ni
Smooth pale green with thin white side stripes, tapering towards the head, and it moves by arching its back into a loop because it lacks the middle pairs of prolegs.
In the record 8,810 georeferenced records · half of them Jun–Aug · most distinctive in November · mostly from the United States check on GBIF
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Imported cabbageworm
Pieris rapae
Velvety, uniformly green with a faint yellow line down the back, matching the leaf so closely it is usually found by its dark green droppings rather than by sight.
In the record 3,687,718 georeferenced records · half of them Jul–Aug · most distinctive in July · mostly from the United Kingdom check on GBIF
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Fall armyworm
Spodoptera frugiperda
Brown to green with stripes and four black dots in a square on the second-to-last segment, plus a pale inverted Y on the front of the head capsule. Arrives in a lawn as a moving front.
In the record 13,635 georeferenced records · half of them Jul–Sep · most distinctive in November · mostly from the United States check on GBIF
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Cutworm
Agrotis and Noctua species
Dull, greasy-looking and unmarked, found curled into a tight C just under the soil surface beside a seedling that was cut off at ground level overnight.
In the record 1,987,359 georeferenced records · half of them Jun–Jul · most distinctive in June · mostly from the United Kingdom check on GBIF
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Bagworm
Thyridopteryx ephemeraeformis
You rarely see the caterpillar at all — only a spindle-shaped bag of silk covered in fragments of the host's own needles or leaves, hanging from a twig and moving slowly.
In the record 10,695 georeferenced records · half of them May–Sep · most distinctive in February · mostly from the United States check on GBIF
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Inchworm or cankerworm
Geometridae
Thin, twig-like, with legs at the front and rear only, so it moves by looping. At rest it holds itself out rigidly from a twig at an angle, imitating a shoot.
In the record 24,385,819 georeferenced records · half of them May–Jul · most distinctive in February · mostly from the United Kingdom check on GBIF
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Spicebush swallowtail
Papilio troilus
Smooth green with two huge false eyespots on the swollen thorax that make it look like a small snake, resting inside a leaf it has folded and tied with silk.
In the record 50,421 georeferenced records · half of them Jul–Aug · most distinctive in March · mostly from the United States check on GBIF
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Eastern tiger swallowtail
Papilio glaucus
Plump smooth green with a swollen front end carrying two yellow-and-black eyespots and a thin yellow-and-black band behind them. Young larvae are brown and white, mimicking bird droppings.
In the record 127,549 georeferenced records · half of them Jul–Aug · most distinctive in March · mostly from the United States check on GBIF
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Catalpa sphinx
Ceratomia catalpae
Black and yellow with a shiny black horn, feeding in large groups that can strip a catalpa completely. Found on catalpa and nothing else, which makes it trivially identifiable.
In the record 6,932 georeferenced records · half of them Jul–Aug · most distinctive in September · mostly from the United States check on GBIF
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Hummingbird moth caterpillar
Hemaris thysbe
Pale green with a yellowish stripe on each side and a short blue-green horn, on honeysuckle. It becomes the clearwing moth people mistake for a hummingbird.
In the record 21,951 georeferenced records · half of them Jun–Jul · most distinctive in July · mostly from the United States check on GBIF
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Viceroy caterpillar
Limenitis archippus
Lumpy, saddle-shaped and mottled olive-brown and cream so it reads convincingly as a bird dropping, with two bristly knobs behind the head.
In the record 54,362 georeferenced records · half of them Jul–Aug · most distinctive in June · mostly from the United States check on GBIF
Nothing in this key matches every filter at once. That usually means one observation is off — a colour read in shade, or a size guessed rather than measured. Clear the filter you are least sure about and look again.
Start with the plant, not the picture
Caterpillars are picky in a way that adult butterflies are not. Most species feed on one plant family and many on a single genus, which means the host is doing far more identification work than colour ever will. A green caterpillar could be any of forty things; a green caterpillar on a tomato plant is one of two.
The strongest host associations in North America are worth memorising outright:
| Found on | Almost certainly | Also possible |
|---|---|---|
| Milkweed | Monarch | Queen, milkweed tussock moth |
| Parsley, dill, fennel, carrot tops | Black swallowtail | Anise swallowtail in the west |
| Tomato, pepper, potato | Tobacco or tomato hornworm | Hornworm parasitised by braconid wasps |
| Cabbage, kale, broccoli | Imported cabbageworm or cabbage looper | Diamondback moth, cross-striped cabbageworm |
| Catalpa | Catalpa sphinx | Nothing else, in practice |
| Spicebush or sassafras | Spicebush swallowtail | Promethea moth |
| Wild cherry, in a spring tent | Eastern tent caterpillar | Forest tent caterpillar, on the trunk |
| Violets, at night | Fritillary | Nothing else feeds only on violets |
If the caterpillar is crossing a path or a road it has almost certainly left its host to pupate, and the host filter will not help. That is the one case where you fall back on texture and colour — and it is also why woolly bears, which do exactly this every autumn, are the most photographed caterpillar in North America.
The stinging ones, and how to recognise them before you touch
Roughly two dozen North American caterpillars can sting, and five of them account for nearly every emergency-room visit. The mechanism is not a bite: hollow spines connected to venom glands break off in the skin and keep releasing venom, which is why the pain builds over the first ten minutes rather than fading.
The reliable warning signs, in order of usefulness:
- Branched or clustered spines — io, saddleback, buck moth, spiny oak slug. Simple single bristles are usually harmless; spines that themselves branch into more spines are the dangerous pattern.
- A slug-like body with no visible head or legs. The slug caterpillars (family Limacodidae) include most of the worst stingers, and they all look like a small flattened blob glued to the underside of a leaf.
- Dense fur that looks soft and inviting. The puss caterpillar hides its venomous spines entirely under a coat of long hair that looks like a scrap of felt. Anything that makes you want to stroke it should not be stroked.
- Tufts, pencils and toothbrush ridges. Tussock moths cause dermatitis rather than a true sting, but the reaction can be substantial and the hairs persist on cocoons and shed skins for months.
If you are stung: lift the embedded spines out with adhesive tape applied and pulled off repeatedly before you touch the area with anything else — rubbing pushes them deeper. Then wash with soap and water, apply ice, and take an oral antihistamine. Seek medical care for chest pain, difficulty breathing, extensive swelling, stings around the eye, or in a child with a known allergy history.
The reverse rule is worth stating too: a great many alarming-looking caterpillars are entirely harmless. Cecropia, luna, mourning cloak and fritillary caterpillars all bristle with spines and none of them sting.
Why the same species can look like two different animals
Three sources of variation defeat photo-matching more often than anything else, and knowing about them prevents most misidentifications.
Instars. A caterpillar moults four or five times, and the early stages frequently look nothing like the last one. Eastern tiger swallowtail larvae start out brown and white as convincing bird droppings and finish as fat green snake-mimics. Black swallowtails begin black with a white saddle. If your caterpillar is under a centimetre, expect the field-guide picture to be wrong for it.
Colour morphs. Many species come in more than one colour with no other difference. Spicebush swallowtails turn yellow-orange before pupating. Buck moths and armyworms range from pale green to near-black depending on density and temperature. Colour is the weakest of the four filters here for exactly this reason, and it is the one most people start with.
Parasitism. A hornworm covered in what look like grains of white rice is carrying the cocoons of a braconid wasp that has been eating it from the inside. It is still a hornworm, it will not survive, and gardeners should leave it in place — those wasps are the most effective hornworm control available.
What it will turn into, and whether that changes anything
The single most common follow-up question is whether the caterpillar becomes a butterfly or a moth. In practice the distinction runs almost exactly along the line this key already uses.
Smooth, naked caterpillars — swallowtails, monarchs, cabbageworms, loopers — become butterflies and moths in roughly equal numbers, and they pupate either as a naked chrysalis attached by a silk button and girdle, or underground.
Hairy, tufted and spiny-with-hair caterpillars are almost always moths. Butterflies with spiny larvae exist — fritillaries, mourning cloaks, question marks — but no North American butterfly has a furry caterpillar. So a fuzzy caterpillar is a moth, essentially without exception.
Whether it matters depends on why you are asking. For a gardener, the practical split is between the handful of species that actually damage a crop — hornworms, cabbageworms, loopers, armyworms, cutworms — and the great majority that eat a few leaves off a tree that does not notice. Tent caterpillars and fall webworms look catastrophic and are, in a healthy tree, cosmetic. Removing them by hand or with a jet of water is sufficient; spraying a whole tree to control webworm kills the parasitoid wasps that would have done it for you next year.
Rearing one, if you want to see what it becomes
Raising a caterpillar to adulthood is the most reliable identification method available, and it takes two to four weeks for most species. Four things matter and the rest is detail.
- The right host plant, fresh, every day. Most caterpillars will starve rather than switch. Take the plant it was found on, and if you do not know what that was, this is not going to work.
- Ventilation and no standing water. A jar with a mesh lid beats a sealed container. Condensation kills more reared caterpillars than anything else, and mouldy frass is close behind — clean the container daily.
- Somewhere to pupate. A twig to hang from, or a few centimetres of slightly damp soil or leaf litter for the many species that pupate underground.
- Cool for the winter. A caterpillar collected in autumn will usually overwinter as a pupa and needs a genuinely cold spell — an unheated shed or garage — before it will emerge. Kept warm indoors it either emerges in December and dies, or never emerges at all.
Release the adult where you found the larva, and do not move species between regions. If you did not collect it locally, it should not be released at all.
What this key covers
34 entries covering the species people in North America actually find: garden pests, the conspicuous large moths, the tent-builders, the stingers, and the butterflies whose larvae are recognisable. North America has over 11,000 moth and butterfly species and the great majority have caterpillars that are small, brown, nocturnal and separable only by an expert with a key and a microscope.
So a specimen that matches nothing here is far more likely to be one of the thousands of unremarkable noctuid and geometrid larvae than something rare. If it matters — a crop problem, a sting, a school project — photograph it in place with the host plant visible and something for scale, and submit it to BugGuide or iNaturalist, where regional specialists identify submissions for free. Include what plant it was eating; without that, even an expert is guessing.
What the observation record shows
Every entry in this key that carries a scientific name is matched against GBIF, the international register of biodiversity records, and against iNaturalist. That puts a hard number behind 34 of the 34caterpillars here: 5,886,602 georeferenced records across the 32 entries that resolve to a single species, spanning 12 families, the oldest of them collected in 1958. The snapshot was taken on 2026-09-04.
That evidence is not spread evenly, and it is worth knowing before you trust a narrow result. The five best-recorded caterpillars in this key hold 85% of all the records between them: Imported cabbageworm alone accounts for 3,687,718, while Buck moth caterpillar has 1,061. A common thing is common in the data too, so when a filter narrows to one frequent entry and one rare one, the frequent one is usually the answer — and the record count is the quickest way to see which is which. The same skew applies geographically: 37% of these records come from the United Kingdom, so the key describes what is reported there far better than it describes anywhere else.
When these are actually reported
Half of every record for this group falls in July–August. A raw month count measures two things at once — when the organism is about, and when people are outdoors with a camera — and the second effect is large enough to give almost anything a summer peak. The line on the figure divides each month by the baseline for every species in every Orvik key, which answers a different question: relative to when people record anything at all, when are these caterpillars recorded? Values above 1.0 are the months that belong to this group rather than to the season. On that measure 20 of the 32caterpillars here peak outside the warm half of the year — Monarch, Eastern tiger swallowtail, Black swallowtail among them. Those are the ones a seasonal rule of thumb gets wrong.
Records behind each entry
Sorted by how much evidence exists, not by how likely you are to meet one. The peak month is the effort-adjusted figure, and it is left blank wherever the sample is too thin for the month-to-month wobble to mean anything.
| Entry | Accepted name | Rank | GBIF records | Research-grade | Half fall in | Peak, adjusted | Most reported from |
|---|---|---|---|---|---|---|---|
| Imported cabbageworm | Pieris rapae | species | 3,687,718 | 262,993 | Jul–Aug | July | the United Kingdom |
| Monarch | Danaus plexippus | species | 799,895 | 532,510 | Jul–Sep | January | the United States |
| Mourning cloak caterpillar | Nymphalis antiopa | species | 247,233 | 96,125 | Apr–Jun | April | Finland |
| Spongy moth | Lymantria dispar Linnaeus, 1758 | species | 146,176 | 83,343 | Jun–Jul | June | the Netherlands |
| Eastern tiger swallowtail | Papilio glaucus Linnaeus, 1758 | species | 127,549 | 207,099 | Jul–Aug | March | the United States |
| Black swallowtail | Papilio polyxenes Fabricius, 1775 | species | 118,300 | 142,960 | Jun–Aug | February | the United States |
| Woolly bear | Pyrrharctia isabella J.E.Smith, 1797 | species | 73,490 | 102,854 | Aug–Oct | October | the United States |
| Great spangled fritillary caterpillar | Speyeria cybele | species | 62,911 | — | Jun–Jul | June | the United States |
| Viceroy caterpillar | Limenitis archippus Cramer, 1775 | species | 54,362 | 51,860 | Jul–Aug | June | the United States |
| Polyphemus moth caterpillar | Antheraea polyphemus Cramer, 1775 | species | 53,407 | 80,988 | May–Jul | February | the United States |
| Spicebush swallowtail | Papilio troilus Linnaeus, 1758 | species | 50,421 | 65,707 | Jul–Aug | March | the United States |
| Fall webworm | Hyphantria cunea | species | 50,172 | 78,851 | Jun–Aug | November | the United States |
| Luna moth caterpillar | Actias luna Linnaeus, 1758 | species | 47,535 | 69,812 | May–Jul | March | the United States |
| Eastern tent caterpillar | Malacosoma americana | species | 46,809 | 66,138 | Apr–May | April | the United States |
| Hickory tussock moth | Lophocampa caryae Harris, 1841 | species | 41,768 | 60,314 | Aug–Sep | October | the United States |
| Yellow woolly bear | Spilosoma virginica Fabricius, 1798 | species | 39,530 | 73,822 | Jun–Aug | October | the United States |
| Milkweed tussock moth | Euchaetes egle Drury, 1773 | species | 31,712 | 47,522 | Aug–Aug | August | the United States |
| Forest tent caterpillar | Malacosoma disstria Hübner | species | 29,306 | 41,719 | Apr–Jun | April | the United States |
| Io moth caterpillar | Automeris io Fabricius, 1775 | species | 24,812 | 33,351 | May–Jul | December | the United States |
| White-marked tussock moth | Orgyia leucostigma J.E.Smith, 1797 | species | 24,554 | 42,821 | Jun–Aug | October | the United States |
| Hummingbird moth caterpillar | Hemaris thysbe Fabricius, 1775 | species | 21,951 | 30,581 | Jun–Jul | July | the United States |
| Tobacco hornworm | Manduca sexta Linnaeus, 1763 | species | 21,557 | 33,018 | Jul–Aug | October | the United States |
| Cecropia moth caterpillar | Hyalophora cecropia Linnaeus, 1758 | species | 13,844 | 20,547 | Apr–Jun | February | the United States |
| Fall armyworm | Spodoptera frugiperda J.E.Smith, 1797 | species | 13,635 | 23,372 | Jul–Sep | November | the United States |
| Bagworm | Thyridopteryx ephemeraeformis | species | 10,695 | 18,740 | May–Sep | February | the United States |
| Puss caterpillar | Megalopyge opercularis | species | 9,349 | 13,461 | Apr–Jul | November | the United States |
| Cabbage looper | Trichoplusia ni | species | 8,810 | 5,600 | Jun–Aug | November | the United States |
| Spiny oak slug | Euclea delphinii | species | 8,443 | 10,830 | Jun–Jul | June | the United States |
| Catalpa sphinx | Ceratomia catalpae Boisduval | species | 6,932 | 10,617 | Jul–Aug | September | the United States |
| Saddleback caterpillar | Acharia stimulea | species | 6,702 | 10,281 | Jul–Aug | September | the United States |
| Tomato hornworm | Manduca quinquemaculatus Haworth, 1803 | species | 5,963 | 7,530 | Jun–Aug | October | the United States |
| Buck moth caterpillar | Hemileuca maia Drury, 1773 | species | 1,061 | 13,677 | Sep–Oct | October | the United States |
| Inchworm or cankerworm | Geometridae | family | 24,385,819 | 4,540,304 | May–Jul | February | the United Kingdom |
| Cutworm | Agrotis Ochsenheimer, 1816 | genus | 1,987,359 | 159,012 | Jun–Jul | June | the United Kingdom |
This table is assembled from open data and is free to reuse with a link back to this page. The snapshot behind every Orvik key is published as one downloadable file on the open field data page, with each source's licence terms.
Questions people ask about this
Which caterpillars sting?
In North America the ones that matter are the puss caterpillar, saddleback, io moth, buck moth and the slug caterpillars including the spiny oak slug. Tussock moths and spongy moth cause an itchy rash rather than a true sting. The visual warning signs are branched spines, a slug-like body with no visible head, or dense soft-looking fur — and the safe rule is simply not to pick up any caterpillar that has spines, tufts or fur.
What is the big green caterpillar on my tomato plants?
A hornworm. If it has seven straight white diagonal stripes and a red horn, it is a tobacco hornworm; eight white V-shapes and a dark blue-black horn make it a tomato hornworm. Both eat tomatoes despite the names. If it is studded with white rice-like grains, those are braconid wasp cocoons — leave that one in place, because the wasps emerging from it will control the next generation.
What are the caterpillars in a web in my tree?
In spring, a dense silk tent in the fork of a wild cherry or apple branch is eastern tent caterpillar; the larvae leave the tent to feed. In late summer, a loose grey web wrapping the leaves at the tip of a branch is fall webworm; those feed inside the web. Both look worse than they are — a healthy tree tolerates the defoliation, and pruning out the tent or blasting it with a hose is enough.
Does the woolly bear's brown band really predict the winter?
No. The width of the rust-coloured band tracks the caterpillar's age and how wet the previous growing season was: the band widens with each moult, so an older, better-fed caterpillar has a wider band. The folklore was tested by an American Museum of Natural History curator in the 1940s and has never held up since.
How do I tell a moth caterpillar from a butterfly caterpillar?
The reliable rule in North America is that no butterfly has a hairy or furry caterpillar, so anything fuzzy is a moth. Butterflies do have spiny caterpillars — fritillaries, mourning cloaks and question marks all do — so spines alone are not the test. Beyond that, moth caterpillars often spin a silk cocoon while butterfly larvae form a naked chrysalis.
Why does my caterpillar look nothing like the pictures?
Most likely because it is an early instar. Caterpillars moult four or five times and can change appearance completely: eastern tiger swallowtails start as brown-and-white bird-dropping mimics and end as fat green snake-mimics. Colour morphs are the other cause — armyworms, buck moths and many others vary from pale green to near-black within one species. Filter by host plant and texture rather than by colour when the picture will not match.
What do I feed a caterpillar I found?
The plant you found it on, fresh, every day. Most caterpillars are restricted to one plant family and will starve rather than switch, so if the host is unknown the honest answer is to put it back where you found it. Keep the container ventilated rather than sealed, clean the droppings daily, and give it a twig or a few centimetres of damp soil to pupate in.
Still not sure? Point a camera at it
A filter narrows caterpillars down to a shortlist. Orvik reads the photo itself and names the species, with the look-alikes ranked underneath so you can check the call yourself.