Safety note
Most UK caterpillars are harmless. However, the Oak Processionary Moth caterpillar has barbed hairs that cause skin rashes, eye irritation, and in rare cases breathing problems. If you see caterpillars in nose-to-tail processions on oak trees, do not touch them or any white silken nests on the bark. Report sightings to your local council.
Quick answer
To identify a UK caterpillar: note the colour and pattern, whether it is hairy or smooth, the plant you found it on, and the time of year. Host plant is often the fastest clue — Cinnabar caterpillars (orange-black striped) are almost always on ragwort; black spiny caterpillars on nettles are usually Peacock or Small Tortoiseshell butterflies.
How to identify a UK caterpillar
Identify British caterpillars safely using the host plant, texture, colour and markings, and size.
- 1
Identify the host plant. Note the plant you found it on first — many caterpillars feed on only one or a few plants, so the plant often narrows the ID down fast (for example, ragwort points to the Cinnabar moth, nettles to Peacock or Small Tortoiseshell).
- 2
Check the texture — and stay safe. Note whether the caterpillar is smooth, hairy, or spiny. Do not handle very hairy caterpillars: the Oak Processionary and brown-tail moth have irritating hairs that can cause skin rashes and breathing problems. Look, don't touch.
- 3
Note colour, markings, and features. Record the colour pattern and any horns, tails, or false eyespots — large eyespots and a 'trunk' point to the Elephant Hawk-moth, while a white saddle on a dark body suggests a Comma.
- 4
Check size and season, then match. Use the approximate size and time of year to confirm, then compare against a trusted photo guide such as Butterfly Conservation or the Wildlife Trusts.
Common UK caterpillars
Cinnabar Moth caterpillar
Adult: Cinnabar moth (Tyria jacobaeae)
Appearance: Vivid orange and black stripes — unmistakable
Host plant: Ragwort (Senecio jacobaea) — almost always found on this plant
Season: July–September
Bright colours warn predators it has absorbed ragwort toxins. Very commonly encountered in late summer.
Peacock Butterfly caterpillar
Adult: Peacock butterfly (Aglais io)
Appearance: Black and spiny — covered in fine black bristles; often gregarious in groups
Host plant: Common nettle (Urtica dioica)
Season: June–July
Groups of black spiny caterpillars on nettles in summer are almost certainly Peacock caterpillars. The spines look alarming but are harmless.
Elephant Hawk-moth caterpillar
Adult: Elephant hawk-moth (Deilephila elpenor)
Appearance: Very large; brown-grey with two prominent false eyespots near the front; when threatened, inflates front end to look like a snake head
Host plant: Rosebay willowherb, fuchsia, bedstraws
Season: July–September
One of the most dramatic UK caterpillars — can reach 8 cm. The 'elephant' name refers to the trunk-like front end, not its size.
Comma Butterfly caterpillar
Adult: Comma butterfly (Polygonia c-album)
Appearance: Black with a large white patch on the back (resembles a bird dropping — camouflage)
Host plant: Nettles, hops, elms
Season: June–August
The white patch on an otherwise dark caterpillar is a bird-dropping mimic — excellent camouflage.
Sycamore Moth caterpillar
Adult: Sycamore moth (Acronicta aceris)
Appearance: Bright orange-yellow with tufts of long white or pale yellow hairs along the body; very distinctive
Host plant: Sycamore, oak, field maple
Season: August–September
Striking and often found on the ground when searching for a pupation site.
Oak Processionary Moth caterpillar
Adult: Oak processionary moth (Thaumetopoea processionea)
Appearance: Grey-brown with white hairs; moves in nose-to-tail processions on oak trees
Host plant: Oak trees; also occasionally hornbeam and hazel
Season: May–July
DO NOT TOUCH. The hairs can cause severe skin irritation, eye inflammation, and in rare cases breathing difficulties. If you find a nest (white silken web on oak bark), do not disturb it — report to your local council.
Now established in parts of SE England. Recognisable by the processional behaviour and white nests on oak bark.
UK caterpillars: FAQs
How do I identify a caterpillar?
Note four things: overall colour and pattern, whether it is hairy or smooth (and hair colour/length), the plant you found it on, and the approximate time of year. Most caterpillars have a specific host plant — finding the plant is often the fastest route to the ID. For UK caterpillars, the Wildlife Trusts and UK Moths websites have comprehensive photo galleries.
Are hairy caterpillars dangerous in the UK?
Most hairy caterpillars found in UK gardens are harmless — the hairs provide camouflage or look threatening to predators. However, the Oak Processionary Moth caterpillar is a genuine exception: its microscopic barbed hairs cause skin rashes, eye irritation, and occasionally breathing problems. It is found on oak trees in southeastern England. As a rule: if you are not sure what a hairy caterpillar is, admire it without touching.
Can I move a caterpillar to a different plant?
It is better not to. Most caterpillars are highly specific to their host plant and will not eat or thrive on a different species. If you find a caterpillar somewhere dangerous (on a path, for example), move it gently to the same species of plant nearby rather than a different one.
What are those black spiny caterpillars on nettles?
Very likely Peacock butterfly caterpillars. They live gregariously in groups on common nettles in early to mid-summer, are black with fine spines, and are entirely harmless. Small Tortoiseshell caterpillars (also black and spiny) share the same habitat and food plant — both are nettle specialists.
What is the largest caterpillar in the UK?
The Elephant Hawk-moth caterpillar is among the largest, reaching around 8 cm. The caterpillars of the Privet Hawk-moth and the Convolvulus Hawk-moth are also large — up to 8–9 cm — and bright green. All are harmless.