eTawau > Insects of Borneo > Caterpillars > A tussock moth at the Tawau River Triangle

Four brushes and three pencils

A tussock moth caterpillar on a palm leaflet, Tawau River Triangle — and the five-second test that names it from two metres away

Most caterpillars have to be caught, held and turned over before anyone can say what they are. This one does not. Everything you need is on its back, it is arranged in a pattern nobody else uses, and you can read it standing up.

A hairy caterpillar lying along the edge of a green palm leaflet. Its body is chalky grey-white mottled with dark grey. Four short, dense, flat-topped cream-yellow brushes stand up in a row on its back. A pair of long black hair pencils project forward over a dense mane of grey-brown hair at the head end, and a single long black pencil projects backwards from the tail. A row of small orange-red warts runs low along the side, each carrying a spray of fine pale hairs. The leaflet above the animal has been eaten away, leaving a ragged brown edge.
The whole animal, uncropped of anything that matters. Tawau River Triangle, 23 December 2011, 3.41 in the afternoon. Note the ragged bite out of the leaflet just in front of it — that is not damage, that is lunch.

The pattern is the identification

The same caterpillar with four labels: one pointing to the eaten notch in the leaf above it, one to the four yellow brushes standing on the back, one to the pair of black hair pencils projecting forward, and one to the single black hair pencil projecting backwards from the tail.
Four short dense brushes on the back, two black pencils in front, one behind. That combination is a tussock moth — Erebidae, subfamily Lymantriinae.

Five characters, and they are all visible in the photograph above:

The head is at the front end, hidden under the dense mane of long grey-brown hair.

An enlargement of the rear half of the caterpillar. Two small bright red glands sit on the midline of consecutive segments near the tail, each surrounded by a black patch, and the single long black hair pencil sweeps back from the tail end.
Near the tail, two small red glands on the midline, each in a black patch. A pair of glands like this, on consecutive segments near the rear, is standard in this subfamily — and it is the character most people never see, because it needs enlarging.

The five-second test: look at the back

Around Tawau there are two families of big hairy caterpillars you actually meet, and people mix them up constantly. The site now holds one of each, photographed a year apart, so here they are side by side.

Two photographs side by side. On the left, a lappet moth caterpillar on a concrete post: its back is bare and finely cracked like dried mud, and long pale hair is carried in a skirt low on each side. On the right, the tussock moth caterpillar on a palm leaflet, with four yellow brushes standing up on the back and black pencils front and rear.
Left: a lappet moth (Lasiocampidae), Ikutmaju Saw Mill, 2012. Right: this tussock moth, 2011. Both photographed near Tawau by Wong Fook Yee. Cropped from the originals, not otherwise altered.
A test is only worth writing down if the site can show both halves of it. The Ikutmaju page set out this test in March 2012 with only the lappet to show for it, which meant a reader had to take my word for the other half. Now they do not. If you learn one thing from this page, learn to look at the back — it costs five seconds and it decides the family.

It was feeding, and the evidence is in the frame

The leaflet is eaten away immediately in front of the animal, and the caterpillar is lying along the cut edge. That is where you find them, because that is where the next mouthful is.

It makes this a feeding record rather than a photograph of a caterpillar sitting on a plant, and the difference matters: a caterpillar resting on a leaf tells you nothing about what it eats, and caterpillars wander. This one was at the table.

What palm, though? The leaflet is stiff, parallel-veined and pale along the midrib — a palm, certainly. The Triangle is old oil palm, so a self-sown oil palm seedling is the obvious guess, and tussock moths are among the recognised pests of oil palm in Malaysia, which would make this an ordinary insect doing an economically interesting thing in a papaya garden. But a guess is not a record. The palm is not identified, and the page says so.
Do not pick one of these up. Tussock moth caterpillars carry urticating hairs — barbed hairs that break off in the skin and itch for days. They are hidden among the longer soft ones, so the animal looks far more harmless than it is, and the soft grey mane is exactly what invites a finger. Photograph it and leave it where it is. If you do get the hairs in your skin, adhesive tape lifts more of them out than washing does.

Why there is no size on this record

It was not measured in the field, and — unusually for this site — it cannot be recovered from the photographs either. That is worth explaining, because it changes what to do next time.

On the Canon compacts used for most of the recent records, the camera writes the focus distance into the file. With that, plus the focal length and the sensor width, the photograph measures itself — which is how the Bombalai cotton stainer and the Bukit Gemok caterpillar were sized without a ruler.

The Panasonic DMC-LX5 that took these two frames does not record a focus distance. The fields exist in the maker note and are empty. So for LX5 photographs there is no arithmetic to fall back on, and a scale object in the frame is the only route to a size — a pin, a coin, a ruler, or a thumb held at the animal's distance from the lens.

The record is perfectly good without a size. It says "not measured", which is honest, rather than carrying a number invented from what the family usually measures. A missing figure is a gap; a plausible wrong figure is contamination, and it travels.

The record

23 December 2011 · 3.41 pm · papaya garden — outside the Triangle

On a palm leaflet, beside the part it had eaten

Papaya garden beside the Tawau River Triangle, Tawau, Sabah. Across Jalan Kuhara from the Triangle itself, so outside it, and about as close to it as you can stand. One caterpillar, not measured, lying still along the edge of an unidentified palm leaflet at a point where the leaf had been eaten away. Body chalky grey-white, finely reticulated with dark grey, a black dorsal line towards the rear; four dense flat-topped cream-yellow brushes on the back; a pair of long black hair pencils forward and one backward; two small red dorsal glands near the tail, each in a black patch; a row of orange-red lateral warts, one per segment. Head hidden under a mane of long grey-brown hair. Lepidoptera: Erebidae, subfamily Lymantriinae — a tussock moth. Genus and species not determined. One only; no others seen. Two frames, 15:41:11 and 15:41:25. Not touched; photographed where it sat and left there.
— iNaturalist observation 400969806

How far the name can go, and where it stops

Lymantriinae is a large subfamily — about 350 genera and more than 2,500 species — and a great many of them share this same four-brush plan. The brushes, the pencils and the paired red glands are subfamily characters, not genus characters.

To go further you generally need the adult moth, or the caterpillar in the hand under magnification, or both. No genus is offered here, and a confident-sounding name on this page would be worth less than the honest blank.

Words you may meet

Lepidoptera
The moths and butterflies. Two pairs of wings covered in fine scales — in the adult. The caterpillar is the same animal earlier, and has none.
Erebidae
One of the largest moth families, holding the tiger moths, the tussock moths, the underwings and others. A modern grouping: the tussock moths were long treated as a family of their own, Lymantriidae, and older books still call them that.
Lymantriinae
The tussock moths. Hairy caterpillars with dense brushes on the back, and adults in which the female of many species is flightless.
Tussock
A short, dense, flat-topped tuft of hair standing up on the back. Four of them in a row is the classic arrangement.
Hair pencil
A long, thin, pointed bunch of hairs projecting clear of the body — forward from the front, backward from the tail.
Urticating hair
A barbed or hollow hair that breaks off in skin and causes itching and inflammation. Not a sting: there is no injection, only the hair itself lodged in the skin.
Wart
A raised bump on a caterpillar's body bearing a cluster of hairs. The orange-red row low along each side of this animal.

Related pages

About the photographs. Two frames by Wong Fook Yee with a Panasonic DMC-LX5 in square 1:1 mode, no flash, f/2.8 at 1/320 s, ISO 80, 5.1 mm, taken at 15:41:11 and 15:41:25 on 23 December 2011 in a papaya garden beside the Tawau River Triangle, Tawau, Sabah. Both are camera originals that have never been opened in an editor. For this page they have been cropped, enlarged and labelled; nothing has been sharpened, recoloured, added or removed. The unmarked full frames are attached to the iNaturalist record above.

The subfamily characters, the number of genera and species in Lymantriinae, the account of urticating hairs and the status of tussock moths as oil palm pests are from the general entomological literature; the locality, the date, the times, the behaviour and the eaten leaf are the photographer's own field observations, and the palm is not identified. All photographs © Wong Fook Yee. Page written 17 September 2026. This is the first page on this site filed by scientific classification rather than by the old pairs-of-wings scheme.