Paederus dermatitis (also known as night burn) is a peculiar irritant dermatitis following the contact with an insect  belonging to genus Paederus and its fluid, which contains a blistering, toxic amide, the chemical pederin.

The dermatitis ischaracterised by erythemato-bullous lesions of sudden onset on exposed areas of the body: the neck was the most common site involved followed by the face. A periorbital predilection was present in 75 percent of the facial lesions.

On contact with the conjunctiva and/or cornea, Paederus sp. cause extensive painful peri-orbital swelling and purulent conjunctivitis known as Nairobi eye in Africa. Corneal erosions and blindness can follow. The effect of pederin is not immediately noticeable and only becomes apparent after 1 to 2 days. Dermatitis, often in elongate pattern (dermatitis linearis), is a result of slapping the beetle and crushing and smearing a Paederus against and across the exposed skin, with the following symptoms:

• In mild cases there is a slight erythema that begins at 24 hr and lasts for approximately 48 hr. The patient complaints of peppery, burning, itchy sensation;

• In moderate cases the erythema is marked and begin about 24 hr after contact followed, after about 48 hr, by a vesicular stage, with blisters that enlarge gradually and attain maximal development within another 48 hr. The vesicles dry out over about 8 days, exfoliate to leave smooth, linear hyperpigmentation with wrinkling of the affected skin areas that can persist for a month or more;

• In severe cases erythema, blisters and pigmented scars usually are more extensive due to crushing several Paederus on the skin. Possible additional symptoms are fever, neuralgia, arthralgia, and vomiting.

• Possible secondary infections in affected areas

Paederus does not bite or sting, but accidental brushing against or crushing the beetle over the skin provokes the release of its coelomic fluid which contains pederin, a potent vesicant agent. The morphology and location of the dermatitis change from case to case but usually resembles the accidental dropping of a caustic or hot liquid. The uncommon association of acute dermatitis with minimal or no complaints (no associated painful sensations), the season and the case history facilitates diagnosis.

Pederin is a complex non-protein molecule, highly toxic, more potent than cobra venom. It inhibits protein synthesis and prevents cell division. Pederin (C25H45O9N) is an amide with 2 tetrahydropyran rings, and makes up approximately 0.025% of an insects weight (for P. fuscipes).

Structure of Pederin.

Pederin does not seem to affect the palms of the hands or soles of the feet.  The delay in reaction to pederin and the insensitivity of feet and hands to this material make it more likely that peridin can be trasferred inadvertently (from clothing/bedclothes too) to other areas of the body (e.g., genital or periorbital areas,giving rise to “Nairobi Eye”). 

To mitigate and to avoid of speading  the effects of pederin to other body areas, immediately wash skin that has come into contact with a Paederus beetle with soap and water, or flush eyes with copious amounts of clean water. The dermatitis itself is not transferable. Paederus species belong to the insect order Coleoptera (i.e., beetles) (Gr. "koleos" = sheath; "pteron" = wing,) and the family Staphylinidae (short-winged beetles also know as "rove beetles"), subfamily Paederinae. Rove beetles are very common: they are the largest beetle family in North America (approximately 3100 species).They also occur in Africa, Asia, and South America.

Paederus beetles live in moist habitats : increased contact between people and these beetles may occur after rain showers and/or during a rainy season or an exceptionally wet year. Adults usually are 7-10 mm long and 0.5-1 mm wide, have a black head, posterior abdomen and elytra (this structure covers the wings and first 3 abdominal segments), and a red thorax and anterior abdomen in an alternating black-red-black-red-black, corresponding to head-thorax-elytra-anterior abdomen-posterior abdomen.

The adults are active during the day and are attracted by to light, perhaps more to artificial fluorescent light  at night (Paederus beetles do not seem to be as attracted to yellow incandescent lights). If windows or doors are left wide open, they may move into a house towards a light source  and  inadvertently come into contact with humans. 

Paederus are “skinny” enough to pass through many types of insect screening placed on windows and doors. Once in the house, they may land on a person, whether asleep or awake.  Rove beetles are harmless insects when in contact with the human body, if left unharmed. But if one try to kill or dislodge the insect by swatting crushing or smacking, it may damage it and cause the release and deposition of the insect body fluid  containing pederin on the skin.

Because of its irritant nature, pederin extract is also used as a self-medication for treatment of vitiligo in some parts of the world. Historically, extracts of Paederus beetles have been used by the Chinese since at least the year 739 in the medicinal treatment of boils, nasal polyps, and ringworm. It is an active predator of small insects and other arthropods, including pests of  several  crop-damaging insects food: for this reasond Paederus beetles often are beneficial to agriculture.

To prevent human/beetle contact it needs to prevent pederin-based trauma:

• avoid handling or crushing these insects against exposed areas of skin, etc;

• If a beetle lands on you, try to gently remove it (e.g., blow it off, try to get the beetle to walk onto a piece of paper and then remove it, etc), and wash skin areas that were in contact with the beetle;

• If you crush it, wash your hands, the area where the beetle was crushed, areas that your hands may have contacted after crushing the beetle and clothing that may have been contaminated with pederin due to crushing the beetle;

• If you think that you have may have crushed a beetle but are not sure when this occurred (e.g., while sleeping), shower and wash bedding and clothing;

• turn off fluorescent lights or switch to incandescent bulbs;

• Keep doors closed, and screening on doors and windows in good repair;

• Sleep under a bed net, preferably permethrin-treated;

• Check areas for beetles (especially on wall and ceiling areas around lights) before going to bed.

• If beetles are present, remove or kill beetles by using a knock down insecticide (e.g. a pyrethroid) followed by sweeping up and removal of beetle carcasses. Seal them in a plastic bag and then in the garbage. Avoid handling beetles directly. Wash skin, clothing and equipment that may have been exposed to beetles.

Because the lesion caused by Paederus is just a "irritant contact dermatitis", the reasonable approach is:

• Wash  the affected area with toilet soap and clean water, to remove the irritant;

• Apply topical steroids and oral antihistamines;

• Use antibacterial ointment or oral antibiotics: most of the Paederus species harbor symbiotic gram-negative bacteria that may contaminate the area when the insect is crushed against the skin.