Staphylinidae (Rove Beetles) - Imad Analis Blog

 

Medical and Veterinary Entomology

Rove beetles in the genus Paederus contain pederin (C25H45O9N), a toxin more potent than that of Latrodectus spider venom and the most complex nonproteinaceous insect defensive secretion known. Pederin is synthesized by endosymbiotic gram-negative bacteria (Pseudomonas species) occurring in female Paederus spp. The beetles, which are mostly 7e13 mm long, are found in North, Central, and South America; Europe; Africa; Asia; and Australasia.

Unlike most rove beetles that are dull-colored, many Paederus sp. have an orange pronotum and orange basal segments of the abdomen, which contrast sharply with the often blue or green metallic elytra and brown or black coloration of the rest of the body.  This color pattern may be a form of warning (aposematic) coloration, but a defensive function for pederin has not been demonstrated.

At least 20 of the more than 600 described species of Paederus have been associated with Paederus dermatitis. Skin reactions to the beetles, called Ch’ing yao ch’ung, were described in China as early as AD 739. Most cases of dermatitis have involved tropical species, including Paederus fuscipes (widespread from the British Isles east across Central Asia to Japan and southeast to Australia), P. sabaeus (Africa, where it is called Nairobi fly and champion fly), P. cruenticollis and P. australis (Australasia), P. signaticornis (Central America), and P. columbinus and P. brasiliensis (South America). Species in South American countries are known by various names, such as bicho de fuego, pito, potó, podó, and trepamoleque.

Unlike blister beetles, rove beetles do not exhibit reflex bleeding as a defensive reaction. Pederin contacts human skin only when a beetle is brushed vigorously over the skin or crushed. Because of their general appearance or misunderstandings about their etiology, the resulting skin lesions have been called dermatitis linearis, spider-lick (India and Sri Lanka), and whiplash dermatitis. Thedermatitis may develop on any part of the body; however, exposed areas such as the head, arms, hands, and legs are most often affected. Mirror-image lesions may form where one pederin-contaminated skin surface touches another.

Unlike meloid-induced dermatitis that develops within 18e24 h after contact, the pederine-induced reaction of itching and burning usually occurs 24e72 h after contact with the beetle’s body fluid. The affected skin appears reddened and vesicles form about 24 h after the initial response. The vesicles may coalesce into blistersand become purulent, producing a reaction that is often more severe than that seen after exposure to meloids. The itching may last for a week, after which the blisters crust over, dry, and peel off, leaving red marks or lightened skin areas that may persist for months. Rubbing the eyes with beetle fluid or contaminated hands or beetles flying or crawling into eyes can cause pain, marked swelling of the eyelids and conjunctivae, excessive lacrimation, clouding of the cornea, and inflammation of the iris (iritis). Such ocular lesions seen in East Africa have been called Nairobi eye. Although eye involvement often is very irritating, permanent damage is not common.

Rove beetles live in vegetable debris and under stones and other materials, such as leaf litter. They are predaceous on insects and other arthropods or may eat plant debris.

Paederine staphylinids are most abundant in areas of moist soil, such as irrigated fields and other crop lands, where the adult beetles feed on various herbivorous insects. Consequently, agricultural workers and others working in fields and grassy areas are often affected. Because the beetles are attracted to lights, workers on brightly lit oil rigs and people occupying lighted dwellings in tropical areas are also commonly affected with what has been called night burn.