eTawau > Insects of Borneo > Caterpillars > A caterpillar on a leaf edge, Tawau River Triangle

Bristles in bunches

A caterpillar resting on a leaf edge in the papaya garden beside the Tawau River Triangle. The five-second test can say what it is not, but not what it is.

It was lying along the edge of a leaf, doing nothing at all, on an afternoon walk along the farm path. I took one photograph and walked on. That was how I photographed in 2008. Eighteen years later the one frame still shows enough to say what kind of animal this is, and it shows exactly where the name has to stop.

A caterpillar lying along the curled edge of a green leaf against a blurred green background. Its back is purplish-brown with rows of small black dots and orange-based warts, a broad cream-white stripe runs along its side, and the underside is translucent pale green. Bunches of stiff black bristles stand up from dark warts behind the orange-brown head, and finer bristles spray out from warts along the body.
This is what you would see. Papaya garden beside the Tawau River Triangle, 1 October 2008, 3.41 in the afternoon. The head is at the top left, tucked down against the leaf.

Look at how the bristles grow

The same caterpillar with five labels: the orange-brown head; the dark warts behind the head, each carrying a bunch of stiff black bristles; an orange-based wart on the back with a spray of bristles and black dots in front of and behind it; the cream-white stripe along the side; and the back, which carries no dense brushes.
The bristles come in bunches, and each bunch grows from a raised wart. That is the character this record rests on. Cropped from the original and labelled; nothing else altered.

Most caterpillars carry their bristles one at a time, each from its own small spot. This one does not. Behind the head the bristles stand up in stiff black bunches, several from each dark wart. Along the back, each orange-based wart throws out a spray of finer bristles, with a pair of black dots in front of it and a pair behind.

A wart carrying a bunch of bristles is called a verruca. They are typical of the Erebidae, the family that holds the tiger moths and the tussock moths. That is the direction this record points, and it is as far as I will take it.

The five-second test, used the other way round

This site already teaches one quick field test for hairy caterpillars around Tawau: look at the back. A tussock moth has four short dense brushes standing up on it. A lappet moth has a bare back, with its long hair in a skirt low on each side. Both halves are on the site: the tussock moth from this same garden and the lappet moth on a gate post at Ikutmaju.

This caterpillar is neither. It has no brushes standing on its back, so it is not a typical tussock. Its bristles are not a skirt of long hair, so it is not a lappet either.

A test tells you what an animal is not, as well as what it is. The five-second test was written to separate two families. It was never a key to every hairy caterpillar in Borneo, and this animal shows why. When a caterpillar fails both halves, the right answer is "something else". Choosing the nearer of the two would be a guess.

How big — what the camera can say

I did not measure it. There is no ruler, pin or finger in the frame.

But this camera, a Canon PowerShot A460, writes the focus distance into the file, and for this frame it says about 9 cm, in macro mode. With the focal length and the size of the sensor, that turns into a scale on the picture. The answer is a body length of roughly 35 to 55 mm.

Treat that as an estimate, not a measurement. At close range these Canon cameras record the focus distance only coarsely, and on another record the camera's figure was out by a third against graph paper in the same frame. The caterpillar is also curved over the leaf edge, so part of it is nearer the lens than the rest. Hence a range and not a number. A scale in the frame beats the camera's own figure every time.

Compare the 2011 tussock moth from the same garden. It was taken with a Panasonic that records no focus distance at all, so that record has no size and cannot have one. The older camera left the better trail.

Where the name stops, and what would move it

Two things would move it:

  1. A second view, from above or from below. The underside and the prolegs are hidden against the leaf, and so is the full arrangement of warts on the back.
  2. The plant. The leaf is not identified. Many moths use only a few plant families, so naming the plant often narrows the moth.

Neither can be had now for this animal. That is why the Tawau River Triangle records made after this one carry more frames.

Do not pick it up. The bristles of some tiger moth and tussock moth caterpillars irritate the skin, and this one has not been identified, so there is no way to know. Photograph it where it is and leave it, which is what happened here.

The record

1 October 2008 · 3.41 pm · papaya garden — outside the Triangle

Resting along the edge of a leaf

Papaya garden beside the Tawau River Triangle, on the Jalan Kuhara side, Tawau, Sabah. Across Jalan Kuhara from the Triangle itself, so outside it. Found on an afternoon walk along the farm path. One caterpillar, lying still along the edge of a leaf of an unidentified plant. Not measured; about 35–55 mm estimated from the camera's recorded focus distance. Head smooth, orange-brown, held low. Back purplish-brown; on each abdominal segment an orange-based wart carrying a spray of bristles, with a pair of black dots in front and a pair behind. Dark warts behind the head, each with a bunch of stiff black bristles. A broad cream-white stripe along the side; the underside translucent pale green. No dense brushes on the back. Lepidoptera: family not determined; the bristles growing in bunches from warts point towards Erebidae. One only. A single photograph; not touched, and left where it was.
— iNaturalist observation 402703797

The garden across the road

The papaya garden is across Jalan Kuhara from the Tawau River Triangle, the block of abandoned oil palm I have been recording for years. It keeps turning up records: a butterfly caterpillar in 2007, this caterpillar in 2008, a weaver ant queen in 2009 and a tussock moth caterpillar in 2011.

My field note gave one reason for that:

"The drain near by keep small insects population thriving."

A drain beside cultivated ground means water all year and soft growth along its banks. In a garden that also has papaya and weeds, that is a lot of food within a few steps.

3.41 pm, twice. This caterpillar was photographed at 3.41 in the afternoon. So was the tussock moth, in the same garden, three years later. That is a coincidence, and it says more about when I go walking than about when caterpillars sit on leaves. But it is a useful reminder that every record from this ground was made in the afternoon, and mornings and nights have not been looked at.

Words you may meet

Lepidoptera
The moths and butterflies. The caterpillar is the young stage; it has no wings, and the adult has two pairs.
Erebidae
One of the largest moth families, holding the tiger moths, the tussock moths, the underwings and others.
Verruca
(plural verrucae) A raised wart on a caterpillar that carries a bunch of bristles rather than a single one.
Seta
(plural setae) The scientific word for a bristle or hair on an insect.
Proleg
One of the soft, stubby false legs on the rear half of a caterpillar, used for gripping. Their number and the hooks on their tips help with identification. They are hidden in this photograph.
Host plant
The plant a caterpillar eats. Many moths use only a few kinds, so naming the plant often narrows the moth.

Related pages

About the photograph. One frame by Wong Fook Yee with a Canon PowerShot A460 in macro mode, no flash, f/8 at 1/125 s, ISO 100, 5.4 mm, taken at 15:41:57 on 1 October 2008 in the papaya garden beside the Tawau River Triangle, Tawau, Sabah. A camera original, never opened in an editor. For this page it has been reduced, cropped and labelled; nothing has been sharpened, recoloured, added or removed. The unmarked full frame is on the iNaturalist record above.

The size range is calculated from the focus distance, focal length and sensor size recorded by the camera, and is an estimate. The meaning of verrucae and the families in which they occur are from the general entomological literature. The locality, date, time, behaviour and the drain are the photographer's own field observations. The plant is not identified. All photographs © Wong Fook Yee. Page written 23 September 2026.