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Genus/Species

 

Loxosceles spp., Brown spiders

Clinical entries

Species

Approx. 100 species.

Taxonomy

Arachnida; Araneae; Araneomorphae (Labidognatha); Sicariidae

Common names

Brown spiders, Violin spiders, Fiddlebacks, Araña de rincon
L. reclusa: Brown recluse spider

Distribution

Main areas of distribution:

  • Temperate to tropical regions of North, Central and South America, including the Caribbean (approx. 85 species).
  • From temperate southern Africa northwards as far as the Mediterranean and southern Europe (approx. 13 species).
  • 2–3 species in China.

Two species have established themselves beyond their original areas of distribution in various parts of the world through unintentional transport by humans; colonisation of new areas is ongoing.

They are:

  • L. laeta: (originally from South America) in Central and North America, Finland, Australia;
  • L. rufescens: (originally from the Mediterranean) in north Africa, Madagascar, southern Europe, Middle East, southern areas of the Commonwealth of Independent States, Myanmar, China, Japan, southern Australia, Pacific Islands (including Hawaii).

Biology

Body length 0.8–1.5 cm, leg length 1.8–3 cm. 6 eyes in a curved line arranged in 3 pairs. Colouring generally light to dark brown. In many species there is a distinctive, dark marking in the form of a violin on the cephalothorax (Fig. 4.41).

 

a

b



Fig. 4.41 Loxosceles reclusa
a Appearance. Note the characteristic violin-shaped marking on the cephalothorax.
b Carapace with the arrangement of the 6 eyes.

 

Shy, primarily nocturnal spiders. Irregular web with cotton-like threads. They prefer dark hiding places outdoors, e.g. under stones, in cracks in stones, under loose bark, under fallen leaves etc. Several species, such as L. laeta and L. rufescens, often live close to humans, in houses, cellars, sheds, barns or animal sheds. In houses they establishes themselves in corners of rooms, behind furniture and pictures etc. The wide distribution of L. laeta and L. rufescens in cooler regions can only be explained by the favourable environment of heated houses. In the natural environment they cannot endure winter temperatures.

Brown spiders are unaggressive and only bite if squashed.

 

Risk

Necrotic arachnidism is frequently associated with loxoscelism. In many cases with an unknown cause in which skin necroses occur after a presumed spider bite, Loxosceles is generally assumed to be the cause. However, it is possible that other spiders can also cause a similar syndrome. Moreover, such consequences are also possible following stings or bites from other arthropods and secondarily due to infection with mycobacteria.

Bites most commonly occur inside dwellings. The bite feels similar to a mosquito sting. Loxosceles envenoming is most commonly known in the New World, but cases have also been described in Israel and South Africa. L. laeta, L. rufescens, L. reclusa, L. gaucho, L. arizonica, L. deserta, L. amazonica, L. parrami and L. intermedia have been blamed for bites in humans, but it is likely that other species like L similis (Chatzaki et al. 2012) can also cause similar symptoms of envenoming. According to a study of Loxosceles bites in Chile, the overwhelming majority of accidents occur inside dwellings, in particular in the bedroom, while the victim is sleeping or getting dressed (Schenone et al. 1989).

Literature (biological)

Lucas 1988, Gertsch 1967, 1983, Schenone and Suarez 1978, Newlands et al. 1982, Levi and Spielman 1964, White et al. 1995

The World Spider Catalog