eTawau > Insects of Borneo > True bugs > A cotton stainer at Bombalai Hill

The commonest bug on the trail

A cotton stainer on a roadside mallow, Bombalai Hill — photographed at last, after twenty years of walking past it

This is a small red insect that lives on a weed. It sits on the flower buds of a scruffy shrub along the first few hundred metres of the Bombalai Hill trail, one or two to a plant, and the plant grows all the way up the roadside. Anyone who has walked to Bombalai has walked past hundreds of them.

Which is exactly why there was no photograph of it on this site until now. The commonest animals are the worst recorded. Everybody assumes somebody else has already done it, and nobody has.

A bright red and orange bug about 14 mm long standing on the flower bud of a small shrub. The head is scarlet, the antennae and long legs are black, a black wedge lies over the front of the body, and the red abdomen behind it carries round black spots. A white scale bar marked 5 mm lies at the lower left.
A cotton stainer, Dysdercus sp., on the flower bud of a mallow. Bombalai Hill trail, 17 September 2026, 10.19 in the morning. The scale bar is 5 mm; the animal is about 14 mm long.

The underside is where the name is

From above, this is a red and black bug and could be one of several families. The photograph that settles it is the one taken seven seconds later, from below.

The same bug seen from underneath, clinging to a plant stalk. The underside of the abdomen is deep red crossed by four broad chalk-white bands that wrap round onto the sides. The head and thorax are red with white marks at the bases of the legs, and the legs and antennae are black.
Turned over: broad chalk-white bands across a deep red belly. That banding is the mark of the cotton stainers, and it cannot be seen from above at all.
A habit worth copying. When an animal is on a stalk and you can move round it, take the underside as well as the top. It costs one photograph. On this record it is the difference between "a red and black bug" and a genus — and the two frames are seven seconds apart, so it cost nothing at all.

A nymph, not an adult — and how to tell in one look

Look at where the wings stop.

The same bug from above with three labels: one pointing to the black spots on the bare red abdomen, one to the short black wing pads, and one to the red head and black antennae.
The wing pads stop short, and the abdomen behind them is bare. An adult would have full forewings covering the whole abdomen, each with a single black spot.

It matters because a nymph cannot be named to species. Colour and pattern change between moults, the keys are written for adults, and the species of this genus in Southeast Asia have been confused with one another in print for more than a century. The record stops at genus, and that is the honest place for it to stop.

The plant is half the identification

Cotton stainers are not generalists. They are specialists on the mallow family, Malvaceae — cotton, okra, hibiscus, kapok and their wild relatives — and they feed by pushing the beak into developing seeds.

A shoot of a small shrub held up against the sky: alternate lance-shaped leaves coarsely toothed along the upper half, a small pale yellow five-petalled flower opening from a green calyx, an unopened bud on a long jointed stalk, and a spent brown flower with the calyx persisting as a cup.
The shrub. Alternate leaves toothed along the upper half, a small yellow flower on a long jointed stalk from the leaf axil, and the calyx staying on as a cup round the fruit. That is a mallow, and to my eye a Sida — one of the commonest weeds of disturbed ground in Sabah. Not confirmed.
So the field note needed correcting, and the correction is the interesting part. My own note said the bug was "wandering among flowers and flower bulbs". It was not wandering. The buds are where the seeds are. On a mallow, a cotton stainer among the flower buds is a cotton stainer at the table.

Why "cotton stainer"

The name comes from the crop. This genus pierces developing cotton bolls to reach the seeds, and the puncture lets in micro-organisms that rot the seed and stain the lint — which is what turns a pretty red insect into a serious pest, and why it has been studied for a century.

There is no cotton within reach of Bombalai Hill. There does not need to be. The wild mallows along a footpath are where this insect lives when there is no crop, and a weedy roadside is not a poor substitute for a cotton field — it is the original home, and the cotton field is the substitute.

How big it was — and how to measure without a ruler

I did not measure the animal in the field. Instead I pushed a dressmaker's pin through one of the flower buds, photographed it, and photographed the same pin on 2 mm graph paper when I got home.

That chain works, and so does a second one that needs no pin at all. The photograph measures itself. The file records the focal length (4.5 mm), the sensor width (6.22 mm) and the distance the lens was focused at (6 cm), and those three numbers give the scale of the picture directly: about 47.5 pixels to the millimetre at the animal. The pin chain gives about 48.

Two methods that share no assumptions, agreeing to within two per cent. That is worth more than either on its own, and it is the general lesson: when a measurement is awkward, look for a second route to the same number rather than a more careful version of the first.

The bug measures about 14 mm from the front of the head to the tip of the abdomen, and a little more if you allow for the body being tilted away from the camera. The flower bud is about 11 mm across.

The record

17 September 2026 · 10.19 am · Bombalai Hill trail

On the flower buds of a mallow, beside the plantation road

Bombalai Hill (Bukit Bombalai) trail, Tawau Hills Park, Tawau, Sabah. The first few hundred metres, beside the 50-metre buffer zone. One bug, about 14 mm, on the flower buds of a common trail-side shrub — Malvaceae, probably Sida, not confirmed. Head scarlet; pronotum orange with a black centre; wing pads black, short, edged white; abdomen red-orange with round black spots above and broad chalk-white transverse bands below. Legs and antennae black. Hemiptera: Pyrrhocoridae — Dysdercus sp., a nymph. Species not determined. One or two on each shrub, and the shrub common along the roadside. Moving over the buds; it dropped off and out of sight after a few photographs. Two frames, 10:19:51 and 10:19:58. Hot, sunny morning, under the annual haze from Kalimantan. Not touched; a flowering shoot was held steady and left on the plant.
— iNaturalist observation 400910722

Where this was: Bombalai Hill

Bombalai Hill is a dormant volcano of about 531 metres, with a crater roughly 300 m across breached to the south. It stands just outside the entrance to Tawau Hills Park, and you do not need a park ticket to climb it. The walk is 1.9 km each way, in two quite different halves: 1 km of unpaved plantation road across private oil palm land, then 900 m of jungle trail on government protected land.

This record comes from the first half, and that is the point of it. The mallow this bug lives on is a weed of open, disturbed, sunny ground — a plantation verge, not a forest floor. So the commonest insect on the walk to Bombalai lives on the part of the walk that is not forest, in the very strip of plantation that cuts Bombalai Hill off from Tawau Hills Park.

That is not a complaint about the plantation. It is a reminder that the edges are full of life too, and that they are the easiest place in Sabah to watch an insect closely — no permit, no ticket, and the animal at waist height in good light.
You may handle this one, but you need not. A cotton stainer has no sting and does not bite people; the beak is for plant seeds. It will, like most bugs of this group, produce a smell if you pick it up, and it will drop off the plant and vanish into the grass — which is what this one did. Bend the shoot gently, photograph it where it sits, and let the branch go.

Words you may meet

Hemiptera
The true bugs. Insects that feed through a beak — a jointed tube that pierces and sucks — rather than by chewing. Cicadas, aphids, shield bugs and this animal are all Hemiptera.
Pyrrhocoridae
The red bugs or cotton stainers: a family of mostly red and black plant-feeders, many of them specialists on the mallow family.
Dysdercus
The cotton stainer genus. Named for the damage it does to cotton lint, not for its own appearance.
Nymph
A young bug. Bugs do not have a pupa: the nymph looks broadly like the adult and grows into it through a series of moults, its wings appearing gradually as pads.
Wing pad
The short, flat, growing wing of a nymph. It lies against the back and does not work. The clearest way to tell a nymph from an adult.
Malvaceae
The mallow family — hibiscus, okra, cotton, kapok, durian, and the roadside Sida. The food plants of this genus.
Rostrum
The beak. Folded back under the body when not in use.

Related pages

About the photographs. Taken by Wong Fook Yee with a Canon IXUS 285 HS on the Bombalai Hill trail, Tawau, Sabah, on 17 September 2026 at 10:19:51 and 10:19:58 (the bug), 10:26:54 (the pin through a flower bud) and 10:33:05 (the plant), with the pin photographed on graph paper at 11:57:44 the same day. For this page the pictures have been cropped and two of them labelled; nothing has been sharpened, recoloured or removed. The unmarked full frames are attached to the iNaturalist record above.

The family and genus characters, the host-plant range and the account of cotton staining follow the Pacific Pests and Pathogens fact sheet on cotton stainers and the published description of Dysdercus cingulatus. The height of Bombalai Hill and the size of its crater are as published for Mount Bombalai; the trail distances, the locality, the weather and the circumstances of the find are the photographer's own field observations. All photographs © Wong Fook Yee. Page written 17 September 2026.