The name ‘caterpillar’ comes from the old French word chatepelose, which means ‘hairy cat’. Caterpillars are the eating and growing stage of butterflies and moths. Many are green but others are intricately patterned, which makes them straightforward to identify.
While a few caterpillars might be considered minor pests because they nibble leaves or veg, most are discreet and secretive, feeding only on their allotted wild plants in quiet corners. Some however, including box tree caterpillar, can devastate plants.
Not all caterpillars are hairy (a defence against being eaten by birds, some of which choke on the bristles), with many being camouflaged like leaf curls or twigs, or warningly coloured (aposematism) to show that their bodies have stored distasteful chemicals from poisonous leaves.
When fully grown, most moth caterpillars descend to the ground and burrow into loose soil to spin a silk cocoon for the chrysalis, in which the earth-bound maggot magically transforms into an aerial adult. Butterfly caterpillars tend to make their chrysalis on or near their foodplant.
How to identify caterpillars
When finding caterpillars, the biggest clue to identifying them is to take note of where you found them. Many have specific host (food) plants and so if you find a caterpillar on a leaf you will be able to narrow down its identity by looking up caterpillars that feed on that type of leaf. For example, caterpillars found on nettles could be the larvae of small tortoiseshell, peacock, red admiral painted lady or comma butterflies, or the larvae of the garden tiger or mother of pearl moths. Secondly, take note of whether they are present individually or in a clump, as some species lay one egg at a time, while others lay all of their eggs together. So, of the five butterfly species listed above, only the comma, painted lady and red admiral will be found individually, the peacock and small tortoiseshell will be found in large clumps, usually beneath a silken ‘tent’ to protect them from predators. This can help you narrow down your identifucation.
When looking for caterpillars, bear in mind that some have evolved complex ways to protect themselves from predators. This may include hiding within its foodplant, feeding at night and hiding by day, or covering itself in a silken tent that resembles a spider web. Make sure you know what you’re looking for before you go out to find it, as this will help you locate even the trickiest of caterpillars.
If you find a caterpillar on the ground it’s probably looking for somewhere to pupate. Make sure it’s safe (away from the pavement or road) and take a photo of it. You can then look it up when you get home.
Bear in mind that this article relates to caterpillar identification in the UK – if you’re looking for a caterpillar identification in another country, make sure you find a page or app dedicated to identifying caterpillars in that country.
Here is a selection of some of the most common species of caterpillar found in gardens.
Poplar hawk-moth (Laothoe populi)
Size: 65-70mm
Where to find them: on or near its foodplant – look for them camouflaged, hiding beneath a leaf
What they eat (foodplant): poplars (including white poplar), aspen and willows
When you seem them: June to October
The poplar hawk-moth caterpillar has a sleek, plump, heavy body in bright green, sometimes with a glaucous blue or turquoise sheen, and slim, pale, diagonal flashes and pinkish spots along each side of the back. Pale-pink tail horn.
Elephant hawk-moth (Deilephila elpenor)
Size: 85-95mm
Where to find them: on or near its foodplant
What they eat (foodplant): willowherbs and fuchsias
When you seem them: July to September
The elephant hawk-moth caterpillar has a bronze, brown to greenish body, with eye spots behind head and tail thorn. If disturbed it squeezes its front segments into a narrow trunk, inflating its eye-spots into a snake-like head.
Garden tiger moth (Arctia caja)
Size: 60-70mm
Where to find them: on or near its foodplant
What they eat (foodplant): a variety of food plants, including nettles, docks and hound’s tongue.
When you seem them: August to October, April to June
The garden tiger caterpillar has a black upper body and ruddy brown lower body, with long, pale hairs all over. A very hairy caterpillar, it’s known as a ‘woolly bear’, and has a mesmerising undulating gait.
Cinnabar moth (Tyria jacobaeae)
Size: 25-30mm
Where to find them: on or near its foodplant
What they eat (foodplant): ragwort, occasionally groundsel
When you seem them: May to August
The cinnabar moth caterpillar has yellow and black bars with sparse, long, pale hairs. It shreds its food plants to bare stalks, leading to local population crashes.
Vapourer moth (Orgyia antiqua)
Size: 35-40mm
Where to find them: on or near its foodplant
What they eat (foodplant): deciduous trees and shrubs, including cotoneaster and pyracantha
When you seem them: May to September
The vapourer moth caterpillar is a psychedelic, animated boot brush, with prominent short, yellow or orange dorsal tufts, and a long, black head and tail whisker fluffs. Mature larvae can often be found resting on their foodplant in late summer.
Mullein moth (Cucullia verbasci)
Size: 45-50mm
Where to find them: on or near its foodplant
What they eat (foodplant): mulleins, figworts and occasionally buddleia
When you seem them: May to July
The mullein moth caterpillar has a plump, pale creamy-green body has yellow blotches and stark black spots. Heavy infestations will shed leaves to bare stalks. Poisonous, so feeds openly during the day.
Brown China-mark moth (Elophila nymphaeata)
Size: 12-15mm
Where to find them: in a floating leaf case, near its foodplant
What they eat (foodplant): pond plants such as frogbit, water plantain, or waterlilies
When you seem them: all year round
The brown China-mark moth caterpillar is unusual among caterpillars, as it’s completely aquatic. It has a smooth, pale-cream or beige body. On hatching, the larva mines inside leaf, but as it matures it cuts and glues two oval leaf fragments with silk to make a floating case.
Drinker moth (Euthrix potatoria)
Size: 65-75mm
Where to find them: on or near its foodplant
What they eat (foodplant): common grasses such as cock’s foot
When you seem them: August to October, April to June
The drinker moth caterpillar looks like a gold and blue blanket, with short tufts of black along its back, and a frayed white skirt. Named for supposed habit of supping dew drops.
Holly blue butterfly (Celastrina argiolus)
Size: 15-18mm
Where to find them: inside the flower bud or berry of its fooplant
What they eat (foodplant): the flower buds, berries and terminal leaves of holly in spring, and ivy in summer/autumn. In gardens will also alternate between pyracantha and snowberry
When you seem them: May to October
The holly blue butterfly is squat, plump, silky-green body has tinges of pink. May be tricky to find as the larvae bore into the side of the bud they are feeding from, and eat it from the inside.
Browntail (Euproctis chrysorrhoea)
Size: 30mm
Where to find them: in a large silken web with its siblings
What they eat (foodplant): brambles and hawthorn. Occasional fruit tree pest
When you seem them: August to October and April to June
The browntail moth caterpillar is black, streaked with whitish marks down each side and two orange bumps near its tail. Each segment with hair tufts. Lives in a communal silk webbing ‘nest’ on its foodplant – be careful touching this caterpillar as its fine hairs have been know to cause rashes and breathing difficulties in some people.
Comma (Polygonia c-album)
Size: 40mm
Where to find them: individually, beneath leaves, on its foodplant
What they eat (foodplant): hops, stinging nettles, elms and currants
When you seem them: May to October
The comma butterfly caterpillar is black with back marked in orange (front) and white (back), especially pronounced nearing maturity, but blurred, and resembling a bird dropping when young.
