eTawau > Insects of Borneo > Caterpillars > Lappet moths at Bako

A hundred on a log

Lappet moth caterpillars in a resting mass at Bako National Park, Sarawak — and the reason nothing was eating them

On the forest floor at Bako, about a hundred metres in from the beach, a fallen log was covered with caterpillars. Not a few. More than a hundred can be counted in a single photograph, packed side by side in curving ranks, every one of them the same size, and none of them moving.

The first thing to say about them is that they are hard to see. Their colour and pattern match the bark closely enough that a person can walk straight past. Shirley Wong saw them; I did not.

A dense mass of large hairy caterpillars covering the bark of a fallen log. They lie packed side by side in curving ranks, dark brown bodies broken by rows of pale dashes, with long fine hair. Their colour and pattern closely match the mottled bark beneath them. A green leafy shoot hangs into the frame at the right.
The mass. Sixty are easy to separate; more than a hundred are there if you look, and it runs past the edge of the frame. Bako National Park, 29 May 2008, 1.29 in the afternoon.

What they are

One caterpillar lifted onto a twig, seen against leaf litter. The body is dark chocolate-brown broken by rows of small cream-white dashes, with a rust-brown band low along the side. Long fine pale-golden hair is carried as a fringe low down each side rather than standing up off the back. The head end is hidden under a dense ochre mane of forward-directed hair. Four labels mark the lateral hair fringe, the absence of standing brushes or pencils, the rows of pale dashes, and the head end.
One animal, lifted onto a twig with a stick. The arrangement of the hair is the identification: a fringe carried low along each side, and nothing standing up off the back.

Lappet moths — Lasiocampidae. The characters are all in the photograph above:

No genus is offered. Several Oriental lappet moths form exactly this kind of dense daytime mass and disperse to feed, but the family is large and the caterpillars of most Bornean species have never been described. The record stops at family, and that is the honest place for it to stop.

This record corrects a test published elsewhere on this site. The Ikutmaju lappet moth page says lappets have "a bare back" with the hair in a side skirt. That is a good way to separate that animal from a tussock moth, but it is not true of Lasiocampidae as a family — plenty of them, this one included, carry hair over the back as well. What holds is narrower and still useful: lappets do not have the four short standing brushes that give tussock moths their name. A field test is a way of telling two animals apart. It is not a description of a family, and this page exists partly to say so.

How big — and who measured it

The same caterpillar laid on pale blue-green graph paper beside a twig, photographed from directly above. A red line traces the curve of its body from tail to head. The grid of the paper is visible along its whole length.
About 100 mm. Measured in the field, on the day, against 2 mm graph paper carried in the bag for the purpose.

About 100 millimetres — ten centimetres. That is the photographer's own field measurement, made with the animal lying on the paper, and it is the figure this page uses.

Why the size is his and not mine. I tried to recover the length from the pixels instead — from the ruling of the paper, and from the focal length, sensor width and focus distance the camera wrote into the file. It did not work. Different methods gave answers spread over four to one, because averaging along a grid that is very slightly rotated destroys the fine ruling, and the camera's own focus figure disagrees with the paper.

The photograph could not settle it and the man holding the animal could. There is a general lesson in that, and it is not a flattering one for clever methods: a scale object in the frame is only as good as your ability to read it, and a note written at the time by the person who was there can be better evidence than anything recoverable afterwards.

Nothing was eating them, and there are two reasons why

A hundred large, soft, slow, stationary caterpillars lying in the open is, on the face of it, a free meal. Nothing took it. No bird came near them, and the long-tailed macaques — which at Bako will lift food straight off a visitor's table — kept away.

There are two explanations, and this record cannot separate them.

These are not alternatives, and that is the interesting part. Plenty of animals carry a chemical or physical defence and camouflage, because being overlooked is cheaper than being tasted. One afternoon's photographs cannot tell you which was doing the work here. The record is better for saying so than it would be for picking the tidier answer.
Do not touch these, and do not sit on that log. The hairs are urticating — barbed, and they break off in the skin. A resting mass sheds them, so the bark and the ground around a mass are contaminated as well as the animals themselves. The one in these photographs was moved with a stick, which is the right way to do it. If you do get the hairs in your skin, adhesive tape lifts more of them out than washing does.

The record

29 May 2008 · 1.13 to 1.29 pm · Bako National Park, Sarawak

A resting mass on a log, a hundred metres in from the beach

Bako National Park, Kuching Division, Sarawak, Malaysian Borneo. On the ground about 100 m in from the beach, on sandy soil under a layer of dry leaves and fallen branches. A dense resting mass of hairy caterpillars on bark, more than a hundred separable in one frame and the mass running past the edge of it, all the same size, packed side by side in curving ranks. Each about 100 mm. Body dark chocolate-brown to black with rows of small cream-white dashes and a rust-brown band low along each side; long fine pale-golden hair as a lateral fringe; no tussocks, no hair pencils; head under a dense ochre mane. Lepidoptera: Lasiocampidae — lappet moths. Genus and species not determined. Stationary throughout; not feeding, not dispersing. No bird or macaque showed any interest. Found by Shirley Wong. One individual lifted onto a twig with a stick, photographed, laid on graph paper, photographed, and left. Nothing collected.
— iNaturalist observation 401219361

Where this was: Bako National Park

Bako is Sarawak's oldest national park — 2,727 hectares on a peninsula north of Kuching, reached by road to Kampung Bako and then a twenty-minute boat ride along the coast. It is small, and that is the point of it: the wildlife is concentrated and easy to meet. Sixteen colour-coded trails, more than 150 recorded bird species, and most of the vegetation types of Borneo inside one short walk — mangrove, peat swamp, padang scrub, dipterocarp forest, cliff and beach vegetation.

This is the first record from Sarawak on the insect pages of this site. Everything else here is from Sabah.

The three days that produced it are written up as a visitor's diary: the crossing and the first afternoon, proboscis monkeys, silver leaf monkeys and these caterpillars, and the macaques, the cicadas and a dragonfly at the stream.

Words you may meet

Lasiocampidae
The lappet moths, also called eggars and tent caterpillars. Stout hairy moths whose caterpillars are hairy, often gregarious, and frequently irritating to handle. Named for the small fleshy flaps — lappets — along the sides of some caterpillars.
Urticating hair
A barbed or hollow hair that breaks off in skin and causes itching and inflammation. Not a sting: nothing is injected, the hair itself lodges.
Gregarious
Living in a group. In caterpillars this usually means a single brood that stays together after hatching, feeding and resting as one mass.
Crypsis
Being hard to see. Colour, pattern and posture that make an animal resemble its background.
Aposematism
The opposite strategy — being conspicuous on purpose, to advertise that you are defended.
Cohort
A group of animals of the same age. A mass of caterpillars all exactly the same size is one brood, hatched together.

Related pages

About the photographs. Taken by Wong Fook Yee with a Canon PowerShot A460 at Bako National Park, Sarawak, on 29 May 2008 at 13:14:43 (the animal on a twig), 13:19:47 (on graph paper) and 13:29:21 (the mass, with flash). All three are camera originals that have never been opened in an editor. For this page they have been cropped, brightened and labelled; nothing has been sharpened, recoloured, added or removed. Further frames from the same fifteen minutes appear on the diary page for that day, and the unmarked full frames are attached to the iNaturalist record above.

The length of about 100 mm is the photographer's own field measurement against 2 mm graph paper. The family characters and the account of urticating hairs are from the general entomological literature; the locality, the date, the times, the behaviour of the mass and the absence of predators are field observations made at the time. The caterpillars were found by Shirley Wong. All photographs © Wong Fook Yee. Page written 18 September 2026.