Watch out for the poisonous rove beetle, called Yakedomushi … could give you nasty boils and blisters…

Yakedomushi / Paedarus fuscipes
Yakedomushi / Paederus fuscipes
節足動物門 昆虫綱 コウチュウ目 ハネカクシ科 Staphylinidae
アオバアリガタハネカクシ Paederus fuscipes (Curtis)
(エゾアリガタハネカクシ Paederus parallelus Weise)
(クロバネアリガタハネカクシ Oedechirus lewisius (Sharp))

-beware these proliferating poisonous bugs (during heavy rains) called yakedomushi in Japan, or rove beetles or close species, the Nairobi fly. nasty bugs cause lesions, blisters and boils that take up to 2 weeks to heal. See photos at and

Skin symptoms included erythema, edema, vesicular papules, painful blisters, burning sensation, pruritus, hyper pigmentation and peeling of skin. The commonly involved sites are the face, neck, shoulders and arms. Most afflicted notice the symptoms upon awakening in the morning. The patients were treated with fusidic acid cream and the symptoms resolved within 5 days. These beetles are nocturnally active and enter the room whenever a light source is available. The unintentional crushing of these beetles during sleep causes the release of its hemolymph (paederin) which is the cause of the dermatitis.

Paederus fuscipes Curtis is the poisonous beetle which frequently causes an acute human dermatitis in Japan as well as in number of foreign countries. The author has made experimental and field observations on the life history, bionomics and distributions of the species in Japan. External structures of each developmental stage have also been fully described. The life cycle of this species comprises egg, larva (two instars), pupa and adult. Adults are about 7mm in length, and look like ants. Free pupae are about 4.5mm in length; body slender and curved ventrally, milky white to orange yellow in colour, with a pair of long seta-like processes on the anterior and posterior margins of pronotum, lateral margins of 1st, 3rd to 7th abdominal segments respectively. The second instar larvae are 4 to 6mm in length; body subcylindrical, white to orange yellow in colour, with a pair of urogomphi. The first instar larvae are 2.2 to 3.4mm in length. Eggs are subspherical, 0.6 to 0.7mm in diameter immediately after the oviposition, but increase in size as the development proceeds. The species is widely distributed throughout Japan, from Hokkaido to Kyushu. It seems to be more abundant in warmer regions. The adults are usually found on soil surface or on grasses in dump places, such as marsh or rice-field. At Narimasu, Tokyo, they could be collected by a light trap during the season from the end of April to the end of October, having the peak in June and July. The nocturnal activity of the adults belongs to the pre-midnight type, i. e. more than half of the total number of a night collection by the light trap was obtained within two and half hours after it had become dark. Eggs are usually laid singly into the crevices on the soil surface.

The poisonous substance which causes dermatitis could be detected in every part of the body of adults, pupae, larvae and eggs. It is contained in the body fluid, and leaks out only when a part of the body is injured. Among eight species of the genus Paederus found from Japan, four species, i. e. fuscipes, tamulus, poweri and parallelus were found to contain the poisonous substance, but fuscipes seemed to be the only species of practical importance. Out of 68 species of Staphylinidae collected by light traps in Japan, Paederus fuscipes was also found to be the only species of actual importance as the cause of human dermatitis, though a few others were demonstrated to cause slight skin lesions under experimental conditions.


1 thought on “Watch out for the poisonous rove beetle, called Yakedomushi … could give you nasty boils and blisters…”

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s