Tomcat beetle (semut charlie) near a child's eye: what to do
A small orange-and-black insect lands near your child's eye at night, and by morning there is a burning streak. What the tomcat beetle is, why the skin reacts a day later, what to do in the first minutes, and when the eye needs a doctor.
- The tomcat beetle (semut charlie) is a rove beetle called Paederus. It does not bite or sting. The rash comes when it is crushed or smeared on the skin and releases a toxin called paederin.
- The skin reacts after a delay, usually within 24 to 48 hours, with a red streak that then blisters, so the link with the insect is often missed.
- Do not crush it on the skin. Brush it off, then wash the skin with soap and water, and wash the hands.
- Near the eye, stop the rubbing. Rinse gently with clean water, and keep soap, creams, toothpaste and home remedies away from the eye.
- Go the same day for eye pain, redness of the white of the eye, light that hurts, blurred vision, or a child who will not open the eye.
A small orange-and-black insect lands on a child's face while the family is getting ready for bed, or crawls across a pillow, and a hand swats it. Sometimes nothing happens. Sometimes, by morning, there is a red, burning streak beside the eye.
The insect is usually the tomcat beetle, called semut charlie in Malaysia. This page explains what it is, why the skin reacts the next day, why the eye area needs more care, what to do in the first minutes, and which signs mean a doctor the same day.
What is the tomcat beetle (semut charlie), and does it bite?
It is a rove beetle of the genus Paederus, not an ant, and it does not bite or sting. The Medical Journal of Malaysia describes the species common here, Paederus fuscipes, as 6.5 to 7 mm long, with an orange body, a black head and short blue-black wings. The Star's 2016 warning about them uses the name "Charlie ants".
The same journal paper says the beetles are attracted to light, which is how they reach people at night, and that they live in marshes, along riverbeds and in rice fields. Cases were reported in hostels near a swamp, a river and an oil palm plantation, and the beetles are more common in the rainy months. That fits a home near a field, a swamp or long grass, but flats and hostels were affected too. The action: know the colours, so that you recognise it before a hand does.
Why does a beetle on the skin cause a burn-like rash the next day?
The beetle carries a toxin called paederin in its body fluid. When it is crushed or smeared on the skin, the toxin is released. DermNet says the redness follows "brushing against or crushing the beetle against the skin", appears 24 to 48 hours later as a streak, and then blisters. The Malaysian journal paper says it begins "most often within 24 hours". The skin heals over about two weeks, and a darker mark can stay for a while.
That delay is why many families do not connect the rash with the insect. Most students in a series from a Selangor university hostel noticed the rash on waking. In that series, 360 cases were seen at the student health centre in one year, mostly from a hostel beside an oil palm plantation. The same paper lists earlier Malaysian reports: a primary school in Terengganu, with 36 pupils, and flats and dormitories in Penang in 2002, where it says 2,000 people were affected. In the Kelantan hostel cases described in 1993, the face was the most common site, and in one episode the cases were mistaken for food or water contamination.
The action: if a streak appears after a night with insects about, think of the beetle first, and do not scratch the blisters.
Why does it matter if the beetle or the rash is near the eye?
The skin around the eye is thin, and the eye itself can be reached. Doctors call it "Nairobi eye": swelling and blistering of the skin round the eye, or inflammation of the surface of the eye (keratoconjunctivitis), or both. The Selangor hostel paper says it is usually secondary to rubbing the eyes with hands carrying the toxin. A 2022 review in the Oman Journal of Ophthalmology adds that it is usually in one eye and can come from direct contact or from the toxin carried on fingers from elsewhere on the skin.
The same review reports that the toxin is a weak base that does not penetrate the cornea and conjunctiva well, so the damage is usually limited. Lesions of the eyelid and the white of the eye healed in about 10 days to 2 weeks, while corneal involvement can take up to 50 days. Temporary blindness has been reported, and darker marks on the skin that last for months. Rubbing with contaminated fingers is the route the Selangor paper names, which is why the advice below starts with the hands.
The action: treat any beetle contact near the eye, or a rash that reaches the lids, as an eye matter and not a skin matter.
What should I do in the first minutes?
Do not crush it on the skin. DermNet's advice is to "remove any beetle found on the skin without crushing it", and to "wash skin in contact with a rove beetle with soap and water". The Malaysian paper from 1993 says the same: wash at once, because a beetle smeared on the skin is the problem. Brush it off with a tissue or a piece of paper, without pressing, then wash the area with soap and water, and wash your hands and your child's hands.
If the toxin may be near the eye, keep your child from rubbing. Soap is for the skin and not for the eye. For the eye, rinse gently with clean water that is not hot, with the eyelids held open, as for any irritant; the same gentle rinse is described in something in my child's eye: sand, an eyelash or a speck, and a full account of rinsing is in chemical splash in a child's eye: the first sixty seconds. None of the Paederus sources gives a rinse time, so the duration is not part of this page.
Leave out toothpaste, mud, oils and creams. In the Selangor series, students who used calamine lotion reported little effect, and the paper notes that toothpaste and mud, used in East Africa, were found to be ineffective. Steroid and antibiotic creams are a doctor's decision, particularly near the eye. The action: wash, rinse, stop the rubbing, then look at the eye in good light.
When does my child need a doctor the same day?
Go the same day if the eye itself is involved. The American Academy of Ophthalmology teaches parents a short rule, RSVP: redness, sensitivity to light, vision change or pain, and it advises prompt care when two or more come together. For this beetle, the signs that matter most are:
- Eye pain, or a child who will not open the eye.
- Redness of the white of the eye, not only of the skin around it.
- Light that hurts, or a child who turns away from a bright room.
- Blurred vision, or a child who says they cannot see properly with that eye.
- Swelling that is closing the eyelid, or blisters on or near the lid edge.
The NHS adds that any change to sight after an eye injury, or severe pain, needs emergency care. A blistering streak near the eye with a comfortable, white eye still deserves a doctor soon, because the skin rash is treated by a doctor, and it can be mistaken for other things, including herpes infections and impetigo. The two pages to read next are my child says their eye hurts, and when to go today and swollen eyelid in children: when it is urgent. The action: if you cannot decide, go. Take the child, and a photograph of the beetle if you have one.
How do we keep the beetles away at home?
With the ordinary measures from the public-health sources, which are about the home and not about the child. The Malaysian papers recommend fine-mesh screens on windows and ventilation panes, and clearing long grass and decaying plant matter from around the house. DermNet adds insect-proof netting at night, and lights that do not give off ultraviolet light. Beetles come to light, so a lit room with an open window is the invitation; closing doors and windows at dusk and turning off lights not in use help.
Those sources are written for hostels, schools and camps, and none tests a home measure in a child's bedroom, so none of this is a guarantee. The 1993 paper called insecticide impractical, because it has to be applied to the beetles' habitat. The household checklist for safety is in eye safety at home. The action: screens on the windows and lights off near open ones, in the rainy months most of all.
- Pain, or a child who will not open the eye.
- Redness of the white of the eye itself.
- Light that hurts, or a child who turns away from a bright room.
- Blurred vision, or a child who says they cannot see properly with that eye.
- Swelling that is closing the lid, or blisters on or near the lid edge.
Common questions
What is a tomcat beetle, and is it the same as semut charlie?
Does the tomcat beetle bite or sting my child?
Why did the rash come the next day, and not at once?
What is Nairobi eye?
What should I do first if a tomcat beetle lands on my child's face?
Should I put toothpaste, oil or a cream on the rash?
When should I take my child to a doctor the same day?
How do I keep tomcat beetles out of the house?
- Medical Journal of Malaysia · Paederus dermatitis amongst medical students in USM, Kelantan (Mokhtar, Singh and Ghazali, 1993) · mail.e-mjm.org
- Southeast Asian Journal of Tropical Medicine and Public Health · Dermatitis caused by Paederus fuscipes in student hostels in Selangor, Malaysia (Heo et al., 2013) · www.tm.mahidol.ac.th
- Oman Journal of Ophthalmology · Nairobi eye, "Wake and see" disease (Sadhasivamohan et al., 2022) · pmc.ncbi.nlm.nih.gov
- DermNet · Paederus dermatitis · dermnetnz.org
- The Star · Beware of Rove beetles (16 November 2016) · www.thestar.com.my
- American Academy of Ophthalmology · Common eye problems in children: symptoms every parent should know · www.aao.org
- NHS · Eye injuries · www.nhs.uk