Spiders

Arachnids, Arachnida, are a class of arthropods. Arachnids include weaver spiders, but also daddy-weavers, scorpions, pseudo-scorpions and mites (including ticks).

There are about 40,000 species worldwide, only a few are of medical importance. Europe is also home to several species of spiders whose bite can penetrate human skin and whose venom causes reactions. Climate changes are causing certain poisonous spiders to spread in Germany as well,

In contrast to the three-part body of insects, the body of arachnids is two-part, Prosoma (front body) and Opisthosoma (abdomen). These limbs can be clearly separated from each other (e.g. web spiders, scorpions). In weavers, roller spiders and mites, they are fused together. The most important feature of arachnids are 4 pairs of legs (insects have 3 pairs of legs).

Other extremities are transformed into tools such as poison claws, scissors, palpation or mouth parts. Most spiders are hunters who kill their prey with poison. Spiders inject poison when biting to paralyze or kill prey.

Spider bites (rare) are usually misdiagnosed in humans. Mostly it is a matter of bite reactions of insects. Epidemiological observations originate from Switzerland (Nentwig W et al. 2013). In a 2-year period, 14 spider bites were verified in Switzerland. 5 species from 4 families were identified: Zoropsis spinimana (5 cases), Cheiracanthium punctorium (4 cases), Tegenaria atrica (3 cases) and 1 case each of Malthonica ferruginea (= Tegenaria ferruginea) and Amaurobius ferox (Amaurobiidae).

All bites caused relatively mild symptoms such as moderate to severe local reactions at the bite site with circumscribed redness and swelling. Slight system reactions were rare. In Switzerland, the incidence of spider bites is estimated at 10-100 per 1 million inhabitants.

The bite of Loxosceles rufescens can lead to skin necrosis. Systemic reactions such as fever, nausea, scarlatiorme or morbilliform exanthema are rarer. The bites of the "black widow spider", the black widow (Lactrodectus tredecimguttatus), a weaver spider endemic to the Mediterranean region, can lead to priapism, muscle cramps, hpertension and tachycardia.

Spider bites are treated symptomatically (locally antiphlogistic; systemically antipyretic in rare fever reactions)

1. Brehler R (2017) Insects and arachnids as triggers of toxic and allergic reactions in Germany. Allergo J Int 26: 129-1136
2. Nentwig W et al (2013) A two year study of verified spider bites in Switzerland and a review of the European spider bite literature. Toxicon 73:104-110.