eTawau > Insects of Borneo > Caterpillars > The dead leaf that was holding on

The dead leaf that was holding on

A caterpillar at the tip of a shrub on the Bukit Gemok trail — and not, after all, turning into anything

I was walking the trail at Bukit Gemok Recreational Forest Park alone on the afternoon of 29 July 2017, and I stopped at a shrub beside the path because something at the tip of it was the wrong colour. A brown, crumpled, angular thing, hanging at the fork where two leaves and a side shoot meet. A dying leaf, I thought — the sort a plant sheds and a spider's thread catches on the way down.

Then I looked again, and it was gripping.

A shrub with opposite elliptic green leaves on a smooth green stem, photographed at eye level in forest shade. A hand at the left holds one leaf aside. At the centre of the picture, at the fork where two leaves and a side shoot meet, hangs a small reddish-brown angular object about the size of a thumb joint, easily mistaken for a crumpled dead leaf. — **The whole shrub, as I found it.** The animal is at the centre of the picture, where the leaves fork. It took me a moment too — which is the entire point of it. My hand is at the left, holding a leaf out of the way.

What I thought it was, and why I was wrong

My first note on this photograph says "seems in the process of transformation" and "from the outer skin, it is probably a butterfly." Both of those are wrong, and the way they are wrong is worth a page of its own, because the animal is built to be misread and I read it exactly as it intends.

It is not turning into anything. It is a full-grown caterpillar, sitting the way this kind of caterpillar sits, and it will sit like that all day.

Close view of the same animal, brightened. A dark reddish-brown caterpillar blotched with purple-black and streaked with pale bone-colour, arched into a tight S against a green stem. The front end is raised and bent back with a glossy dark red head capsule beneath it, the middle of the body grips the stem, and the swollen last segment is carried up over the back and ends in a pair of slender processes tipped with dark bristles. A fine strand of silk hangs in the air to the right. — **The same animal, close.** Reddish-brown, blotched with purple-black, streaked and edged with bone-colour, and folded into a shape no leaf ever quite makes — which is why it works. Photographed thirty seconds after the picture above.

Caterpillar or pupa? Five things that settle it

This is worth learning, because "is it changing?" is the question almost everybody asks about a strange brown lump on a twig, and it has a quick answer. Do not look for the things a caterpillar should have — a poor photograph hides those. Look for the things a pupa cannot have.

Hairs. Fine pale setae stand out along the edges of this body, catching the light against the dark background. A pupa is bare.
A breathing pore. A spiracle shows clearly on the side of the raised front end — a dark oval with a pale rim — with more of them along the body.
A hard head capsule. Glossy, dark red, half translucent, and quite different in texture from the soft blotched skin around it.
Legs that grip. Fleshy prolegs underneath, holding the stem. This is the one that decides it. A pupa hangs, or lies, or is wrapped up. It does not grip.
Nothing a pupa would need. No button of silk, no girdle round the middle, no cocoon, and no shed caterpillar skin crumpled underneath. If this animal had just changed, the evidence would be in the picture. There is none.

The same close view with three labels. One points to the raised, turned-back front end of the caterpillar; one to the pair of slender processes at the rear; one to the prolegs gripping the stem beneath the middle of the body. — **The posture, labelled.** Both ends are lifted clear of the twig and only the middle is holding on. That is not a caterpillar caught halfway through anything — it is how the animal rests.

Two tails, not one

The rear end is the part that gives the family away, and it takes a magnifying glass or an enlarged photograph to see it.

The last segment is swollen, and it is carried up and over the back rather than lying along the twig. At the end of it are two slender processes, each tipped with dark bristles, held out and apart. They are not a forked tail and they are not decoration: they are the animal's last pair of claspers — the gripping legs that most caterpillars use to hold on at the back — remade into a pair of raised spikes and no longer used for holding anything.

Two enlarged views of the caterpillar's rear end side by side, one from each photograph, thirty seconds apart. Both show a swollen segment tapering to two separate slender processes, each ending in fine dark bristles, circled in pink. — **The same structure in both photographs.** Two exposures, thirty seconds apart and from slightly different angles, showing the same pair of processes. One frame could be a trick of the light; two cannot.

That pair puts the animal in the Notodontidae — the prominent moths — and, within that family, in the group known in English as the lobster moths, for the way the caterpillars fold themselves up into something that looks more like a small crustacean than a grub.

It also rules something out. The hook-tip moths (Drepanidae) have caterpillars that look remarkably like this one — brown, humped, angular, with both ends held up — but their rear end tapers to a single point. Counting the tails is the quickest way to separate two families that otherwise need a specialist.

The posture is the animal

Caterpillars in this group are known to rear up when they are disturbed, throwing head and tail into the air to look larger and stranger than they are. So the obvious reading of these pictures is that I frightened it.

I do not think I did. It was already in this attitude when I first saw it, before I was close. And there is better evidence than my memory: I took two photographs thirty seconds apart, the flash fired for both, and between them nothing changed. Nothing was dropped and nothing new was thrown up.

A threat display is a response. It begins when something alarms the animal and it subsides when the alarm passes. This one neither began nor ended. So it is not an alarm — it is simply how the animal sits, all day, every day, until dark.

And that is the thing worth taking away from this page. The animal is not becoming a dead leaf. It is pretending to be one — and it does the pretending with its posture as much as with its colour. Straighten it out and lay it flat along the twig and the disguise collapses: you would see a caterpillar at once. Folded up, with both ends in the air and only the middle holding on, it reads as rubbish caught in a fork.

Colour is the easy half of camouflage. Shape and pose are the hard half, and this animal has to hold the pose all day without moving to keep it.

Why it has no name

The family is as far as this record goes, and it goes there on good evidence. The genus does not.

The Bornean lobster moth that answers to this description is Neostauropus alternus (Walker), also written Stauropus alternus — a polyphagous species whose larvae are recorded on tea, coffee, rambutan, mango and a range of legumes. Its published larval description fits what is in these photographs: dark brown with pale patches and fine lines, paired conical bumps along the back, the eighth segment widened at the sides, and the claspers raised as processes.

But Holloway's Moths of Borneo lists Bornean material of that species only from Brunei and Sarawak, and calls it rarely taken. Not from Sabah. So a Sabah larva would be a genuine addition to the record — and that is exactly the reason not to claim it here. It is posted on iNaturalist at family level, with the genus named as a suggestion, for anyone who knows these larvae to accept or reject.

If you ever find one, here is what to do next. If it is the species the characters point to, it will eventually spin a tough, shining yellow silk cocoon between two leaves — an unusual and memorable object. A photograph of that cocoon, or better a moth reared out of it, would settle in an afternoon what a photograph of the caterpillar cannot settle at all.

How big it was

I did not measure it, and my hand in the first photograph cannot be used as a ruler, because it was holding a leaf aside from the left and was not the same distance from the lens as the animal. Anything measured in finger-widths off that picture would be wrong.

The camera answers it instead. The file records the sensor size, the focal length and the distance the lens was focused at, and those three together give the scale of the picture: about 22 pixels to the millimetre at the animal. On that scale it measures about 34 mm as it sits, front tip to the ends of the processes, and about 43 mm followed along the curve of the body. Call it 40 mm, and say somewhere between 30 and 50. It is a large caterpillar either way.

The record

29 July 2017 · 2.59 pm · Bukit Gemok Recreational Forest Park

At the tip of a shrub beside the hiking trail

Bukit Gemok Recreational Forest Park, Tawau, Sabah. One caterpillar, alone, about 40 mm, at the tip of an unidentified shrub with opposite elliptic leaves, at the node where two leaves and a side shoot meet. Dark reddish-brown blotched with purple-black; paired conical bumps along the back; the swollen last segment carried over the back and ending in two slender bristle-tipped processes. Gripping with the middle of the body only, both ends raised, and motionless. Lepidoptera — Notodontidae, the lobster-moth group. Genus and species not determined. Two frames, 14:59:15 and 14:59:45, flash fired for both. Not touched; photographed where it sat and left there.
— iNaturalist observation 400202493

Bukit Gemok

The hill stands about 428 metres (1,404 feet). A trail runs 1.7 kilometres from the park entrance to a canopy walk 231 metres long — the second longest in Sabah, after the 300-metre walkway at Danum Valley. The climb to the canopy is where most of the animals on this site from Bukit Gemok have been found.

It is worth knowing that this forest is an island. The Bukit Gemok Forest Reserve covers about 445 hectares, and it is cut off from the larger forest of Tawau Hills Park by the plantations and settlements between them, which is why the Sabah Ficus Germplasm Centre at Tawau Hills exists — it is an attempt to plant a corridor of figs back towards it. An isolated hill forest keeps what it has and gains nothing new, so what is recorded there is worth recording carefully.

Other animals photographed on this hill and published here:

Flat-backed millipedes, mating — 2008, on a rock on the forest floor.
A house centipede and its shed skin — 2009.
The Fish Hook Ant — 1 November 2009, the earlier of the two records on that page.
This caterpillar — 29 July 2017.

Do not pick it up, and do not pull the twig. I did not touch this one. An animal that has spent all day holding a pose has spent all day not being eaten, and a hand arriving from nowhere undoes that for nothing. Photograph it where it is and leave the branch as you found it — and if you want to see it properly, move yourself rather than the plant.

Words you may meet

Notodontidae: The prominent moths. A large family, named for a tuft on the forewing of the adults that stands up when the moth is at rest. The caterpillars are famous for strange shapes and modified tails.
Lobster moth: The English name for the group this caterpillar belongs to, from the folded-up, long-legged, hump-backed look of the larva. There is nothing lobster-like about the moth itself.
Clasper: The last pair of fleshy legs at a caterpillar's rear end, normally used for gripping. In this group they are raised into a pair of processes and grip nothing.
Proleg: The soft, stumpy legs along a caterpillar's abdomen — not true legs, and not carried over into the adult moth. They are what holds the animal on.
Spiracle: A breathing pore in the side of the body. Insects have no lungs; air enters through these.
Seta: A hair. Plural setae. Pupae do not have them; caterpillars do.
Pupa: The still stage between caterpillar and moth. A butterfly's naked pupa is a chrysalis; most moths wrap theirs in a cocoon.
Polyphagous: Eating many different kinds of plant, rather than being tied to one.

Caterpillars
The caterpillar that came to the gate post — a big hairy one on painted concrete, and how to tell a lappet moth from a tussock moth
When a weaver ant met a nettle caterpillar — another caterpillar that survives by being recognised rather than by fighting
The Fish Hook Ant · A house centipede · Flat-backed millipedes — the other records from Bukit Gemok
Bukit Gemok Recreational Forest Park · Insects in Bukit Gemok Park — the park itself, how to get there, and the older insect pictures from the trail
Insects of Borneo

About the photographs. Taken by Wong Fook Yee with a Canon PowerShot SX510 HS at Bukit Gemok Recreational Forest Park, Tawau, Sabah, on 29 July 2017 at 14:59:15 and 14:59:45. The flash fired for both, which is why the close views have a black background in the middle of the afternoon — and why the hairs and the breathing pore are visible at all. For this page the pictures have been reduced and brightened, and two of them labelled, because a visitor wants to be shown what to look at. The unmarked originals are attached to the iNaturalist record above, which is where anyone working on the identification should start.

The family characters, the larval description and the Bornean distribution follow J. D. Holloway, The Moths of Borneo, and the published larval diagnosis of the Notodontidae. The date, the time, the camera settings and the scale of the photographs are taken from the files themselves. The locality, the altitude, the trail figures and the circumstances of the find are the photographer's own field observations. All photographs © Wong Fook Yee. Page written 14 September 2026.