eTawau > Insects of Borneo > Caterpillars > A swallowtail caterpillar at SMK Abaka

A passenger on the hump

A young swallowtail butterfly caterpillar beside SMK Abaka, Tawau, and the tiny red animal that walked over it while I watched

It was sitting on the upper side of a broad, glossy leaf at the edge of the old oil palm plantation outside SMK Abaka, about 16 km from Tawau town. It did not move. Something on it did. My field note says:

"Not moving. But this caterpillar has a tinny insect in its head that was moving."
A smooth caterpillar lying on a bright green leaf in sunshine. It is thick and humped at the front, where it is dark brown with short black spines standing up in pairs, and it tapers towards the rear. A broad pale yellow-green band crosses the middle of the body, the rear segments are dark brown again, and the tail ends in a pale fork with two short points.
This is what you would see. The old plantation beside SMK Abaka, 2 August 2009, 4.17 in the afternoon. The head end is on the right.

Why it is a swallowtail

The same caterpillar with six labels: the pairs of short black spines on the hump; the first segment, an orange-brown shield with black spines, with the head beneath it; a dark round spot on the side of the hump; the pale yellow-green band across the body; the forked tail; and the tiny orange mite near the front of the underside.
The shape, the spines and the forked tail. Together they point to the swallowtails, family Papilionidae. Cropped from the original and labelled; nothing else altered.

Four things in these photographs point the same way:

Together they fit the young caterpillar of a swallowtail butterfly, family Papilionidae. The combination looks most like the swordtails and jays, and Graphium is a possibility. But that is a direction, not a name, and this page does not give a genus.

The alternatives, and why they were set aside. Two groups of brush-footed butterflies also have caterpillars with forked tails. The emperors and rajahs carry a large head with horns on it, which you would see at once; this one's head is hidden. The browns have no spines behind the head at all. Neither fits all four characters above.
The caterpillar seen from the front on a green leaf. The rounded orange-brown first segment faces the camera with a short black spine at each side, and behind it the dark brown hump rises with further short black spines at its corners. The pale yellow-green band shows beyond.
From the front. The orange-brown shield of the first segment faces you, and the hump rises behind it. The head is still out of sight underneath. 16:17:00, cropped only.

Where the name stops, and what would move it

  1. The forked scent organ. Every swallowtail caterpillar has one: a soft orange fork that it pushes out from behind the head when disturbed, giving off a strong smell. It was not disturbed, and the organ does not show. A photograph of it would settle the family beyond argument.
  2. The plant. Swallowtails are fussy about what they eat. The swordtails and jays feed mainly on custard-apple, laurel and magnolia relatives. The leaf here is broad and glossy, but it is not identified.

The passenger

The "tinny insect" is the most interesting thing in these photographs, and it is probably not an insect.

An enlargement of the side of the caterpillar's hump. A tiny bright orange animal with a round body and long pale legs stands on the brown skin, with six legs visible. To its right is one of the caterpillar's dark round spots.
Six legs, counted at 16:15:41. Enlarged from the original and labelled; nothing else altered.

Insects have six legs, and so, at first sight, does this. But it has no visible antennae, and its body is not divided into head, thorax and abdomen. Those are the marks of a mite. Adult mites have eight legs, but young mites hatch with only six and gain the last pair later. Six legs is exactly what a young mite would show.

I count six legs in two separate photographs. A fourth pair folded underneath cannot be ruled out, though, so this page does not name the animal beyond probably a mite.

The camera timed it. Photographs taken in sequence record the time of each frame, and here the times track the mite across the caterpillar: It was walking, not attached. Many young mites do ride on insects, some feeding and some simply travelling. Whether this one was looking for somewhere to feed, or was only passing over, these photographs do not say, and I am not going to guess.

How big — not measured

There is no ruler, coin or finger in any of the four frames, so this record has no size.

These four photographs exposed a mistake on another page. The camera writes a focus figure into every file, and on 23 September 2026 I used that figure to give a size for the 2008 caterpillar from the papaya garden. These frames all record 8 or 9 cm, yet the mite is clearly larger in one frame than in another: the camera had moved closer and the figure had not changed. On these Canon compact cameras in macro mode, the figure is only an upper limit, not a distance. The 2008 size was withdrawn the next morning, and that page now says so.
Do not handle it. Swallowtail caterpillars have no stinging hairs, but a disturbed one pushes out its orange scent organ, and the smell stays on your fingers. More to the point, a young caterpillar knocked off its leaf may not find its way back to the one plant it can eat. Photograph it and leave it where it is, which is what happened here.

The record

2 August 2009 · 4.15 to 4.17 pm · old oil palm beside SMK Abaka

Resting on a broad glossy leaf, with a mite walking over it

Old oil palm plantation outside SMK Abaka, about 16 km from Tawau town, Sabah. One caterpillar, not measured, resting on the upper side of a broad glossy leaf of an unidentified plant, not moving. Humped behind the head and tapering to the tail; dark brown at the front and rear with a broad pale yellow-green band across the middle; first segment an orange-brown shield with short black spines, the head beneath it; pairs of short shiny black spines on the hump; dark round spots on the side of the hump; a pale forked tail. Lepidoptera: Papilionidae — a swallowtail butterfly. Genus and species not determined. One only. A tiny orange-red animal, probably a young mite with six legs, walked over it during the two minutes of photographs. Four frames, 16:15:33, 16:15:41, 16:17:00 and 16:17:31. Not touched; photographed where it sat and left there.
— iNaturalist observation 402848121

The place has gone

In 2009 SMK Abaka stood among old oil palms, with a rubber plantation on one side. Since then the old palms have been replanted with young oil palm, and the rubber has been cleared and replanted with oil palm too.

So the ground this caterpillar was found on no longer exists in the form it had that afternoon. An old plantation with undergrowth, broad-leaved plants and a rubber estate next door is a different place from a young, weeded oil palm block. That is what makes an ordinary dated photograph worth keeping: it is a record of what lived on a piece of land before the land changed, and nobody can go back and take it again.

Words you may meet

Papilionidae
The swallowtail butterflies: birdwings, swallowtails, swordtails and jays. Many adults have tails on the hindwings, which gives the family its English name.
Osmeterium
The forked, soft, usually orange scent organ that every swallowtail caterpillar can push out from behind its head when disturbed. Found in no other family.
Instar
A caterpillar's stage between one moult and the next. Young instars of many swallowtails look quite different from the fully grown caterpillar.
Mite
A tiny relative of spiders and ticks (Acari). Adults have eight legs; the young that hatch from the egg have six.
Host plant
The plant a caterpillar eats. Swallowtails use only a few plant families each, so naming the plant often narrows the butterfly.

Related pages

About the photographs. Four frames by Wong Fook Yee with a Canon PowerShot A470 in macro mode, no flash, f/3.0, ISO 100, 6.3 mm, taken at 16:15:33, 16:15:41, 16:17:00 and 16:17:31 on 2 August 2009 beside SMK Abaka, Tawau, Sabah. All are camera originals that have never been opened in an editor. For this page they have been reduced, cropped, enlarged and labelled; nothing has been sharpened, recoloured, added or removed. The unmarked full frames are on the iNaturalist record above.

The family characters, the osmeterium, the host-plant families of the swordtails and jays, and the six-legged young stage of mites are from the general entomological literature. The locality, date, times, behaviour, the moving "tinny insect" and the later replanting of the land are the photographer's own field observations. The plant is not identified. All photographs © Wong Fook Yee. Page written 24 September 2026.