Distribution

1. Worldwide, above all in arid and semi-arid regions
2. Worldwide

Biology

With over 300,000 species, beetles (Coleoptera) form the largest order among the insects. Most are easily recognised by means of their hard shield-like forewings.

In many species, toxic substances have been discovered in various glands, but the only families of real medical significance are the Meloidae and Staphylinidae. They possess substances in the haemolymph and in body tissues that are skin irritants and which are exuded from various parts of the body if the beetle is squeezed slightly or brushed off the skin. Naturally these substances can also come into contact with the skin if the beetle is swatted and crushed.

The genera of Blister beetles (Meloidae) that are relevant for humans are Epicauta, Mylabris, Psalydolytta and Lytta. These are smaller species of roughly 1.5 cm in length, some of which have iridescent colouring. The most important toxin in these beetles is cantharidin. It became known as a dangerous aphrodisiac which is taken in the form of dried "Spanish flies" (Lytta vesicatoria). If it is taken orally this substance is strongly nephrotoxic and even small doses can lead to life-threatening nephritis.

Among the Staphylinidae, the important species all belong to the cosmopolitan genus Paederus. They have an elongated ant-like form between 0.5 and 1 cm long and have only short forewings. They are usually nocturnal and are attracted to light. The alklaloid pederin is considered responsible for the skin-irritating effect of the secretions.

  Fig. 4.89 Paederus sp.

Risk

Skin lesions caused by meloid and staphylinid beetles are chiefly known to occur in the warmer regions of the world, but occasionally also occur in temperate zones. Rashes and blisters form on the affected area of skin and persist for several days. However, they first occur several hours or days after contact, and thus it is quite common that the beetles are not even considered as a possible cause. If the beetles directly enter the victim's eyes or if secretions on the victim's hands are rubbed into the eyes, swelling of the eyelids and conjunctivitis result. This syndrome is known as "Nairobi eye".

In Iran, skin reactions following contact with the species Meloidae and Staphylinidae have been known to occur. In medical terms, Paederus fuscipes is considered the most significant species in that country. In the southern regions of Iran, accidents with toxic beetles are a problem in rural areas with small villages and cities, while in the north, contact with toxic beetles is chiefly an urban problem in the larger cities along the Caspian Sea (Nikbakhtzadeh and Tirgari 2008).

Literature (biological)

Weatherston and Percy 1979, Minton and Bechtel 1989, Monteith and Argent 1987, Nikbakhtzadeh and Tirgari 2008