If someone asked you to name a place with poisonous fauna, what would spring to mind? Perhaps Australia, with infamous snakes like the inland taipan (Oxyuranus microlepidotus), or maybe Brazil, home to dreaded creatures like the yellow scorpion (Tityus serrulatus). Europe, however, would probably be low on the list, as the continent is not known for its menacing fauna.
In recent years, however, fear of a small eight-legged creature has risen in southern Europe, as deaths attributed to one particular spider have been widely publicised. The latest known case occurred just this summer in the Italian town of Bari, where a 23-year-old man died following a suspected bite by a Mediterranean recluse spider, also known as a brown recluse or corner spider. Just a month earlier, a 52-year-old police officer in Palermo died of the same cause.
Europe’s two most feared spiders
If you were fond of poking your hands into every nook and cranny, and were very unlucky, a walk in the Spanish countryside could result in a painful bite from one of the country’s larger arachnids, such as the cork tree spider (Macrothele calpeiana) or the wolf spider (Lycosa tarantula). However, in the Mediterranean region there are only two spider species whose bites are considered a medical concern: the European black widow (Latrodectus tredecimguttatus) and the Mediterranean recluse (Loxosceles rufescens).
The black widow has always had the worst reputation, but there are no documented cases of deaths caused by the bite of its European variant. Moreover, encounters with this striking animal are rare, as it is found in rural areas and builds its erratic webs under tree bark or rocks. The neurotoxic effects of its venom on humans are well known: a complex cocktail of molecules, collectively known as latrotoxins, affect nerve transmission, heart muscle and smooth muscle function, causing a syndrome called latrodectism.
The recluse spider, which usually has a small, dark, violin-shaped spot on its cephalothorax, is another matter entirely. Although it is found in the wild, nowadays it can practically be considered a synanthropic species, meaning it tends to live in close proximity to humans, especially inside houses, garages or workplaces. It often finds dark, dusty hiding places, such as behind or under large pieces of furniture, where it can go unnoticed for long periods of time.
A different kind of venom
Unlike the neurotoxic venom of black widows, the venom of spiders in the sycarid family, to which the Mediterranean recluse belongs, has a necrotic action, meaning it causes the death of body tissue. Among the many proteins found in their venom are phospholipase enzymes, which degrade cell membranes and rupture blood vessels. The two combined effects usually cause a localised reaction at the site of the bite that includes swelling, redness and itching for a few weeks.
In a small percentage of cases, the central area of the bite may develop a necrotic lesion, where the tissue dies and eventually falls off before healing after a few weeks.
This set of symptoms – called cutaneous loxocelism – does not usually have major consequences unless the bite occurs on particularly sensitive areas like the face. Moreover, necrotic progression is less common with the European recluse spider than with some of its Latin American counterparts (L. reclusa and L. laeta), which are considered a significant public health problem in countries like Chile, Argentina and Peru.
In some rare cases, however, necrosis caused by a recluse spider bite can reach the underlying muscle and cause toxic shock syndrome, which includes symptoms such as fever, muscle and joint pain. When caused by a loxosceles bite, this is known as cutaneous-visceral loxoscelism, a condition which, though very rarely, can lead to acute haemolysis (destruction of blood cells), renal failure, shock and, eventually, death.
Loxosceles in Spain
L. rufescens, a species native to the Mediterranean region, has lived among humans for thousands of years. However, its bite is very rare, and official, reliable data on cases of bites is very scarce. Even when a more serious clinical reaction occurs, the patient is rarely able to see, let alone catch, the animal that bit them, meaning that most diagnoses of loxoscelism cannot be completely verified.
This difficulty has also been highlighted by a multidisciplinary research group directed by the University of the Balearic Islands. In an article published this year, they analysed four recent cases of suspected recluse spider bites, and another twelve documented in Spain between 2005 and 2021.
To date, no human deaths have been officially attributed to a recluse spider bite in Spain. The recent deaths in Italy from suspected Mediterranean recluse bites are still something of a mystery – they could be a mere statistical anomaly, or a series of clinical misjudgements.
It could also be that, due to commercial globalisation and the current volume of intercontinental travel, the Italian bites may have been caused by American species of Loxosceles that was accidentally brought into Europe.
This has happened on several occasions with specimens of the much more dangerous genus Phoneutria, which includes the famous Brazilian wandering spiders that have, on rare occasions, appeared in fruit shipments imported from South America. However, there is no official record of any stable population of American recluse spiders or Phoneutria in Europe.
Should we be worried?
Arachnophobia, a widely held fear, is fuelled by horror films and books, as well as sensationalist publications in the press. But the reality is quite different and, at least in Europe, the threat posed by any species of spider is almost negligible.
Over a 23-year period, 1,691 deaths attributed to wasp, hornet and bee stings were recorded in Europe, yet most of us don’t run for the hills when a bee comes sniffing around the jam on our toast.
The fact that deaths from alleged spider bites in a similar period can be counted on the fingers of one hand puts the reality of the situation into context.
Mediterranean recluse spiders are not very aggressive and usually attack only when directly disturbed, so there is little need to worry. If you take the precaution of occasionally cleaning under the sofa or behind the wardrobe, and wear gloves when moving such furniture, the likelihood of a Loxosceles bite landing you in hospital is not much different to that of being struck by lightning.
Este artículo fue publicado originalmente en The Conversation, un sitio de noticias sin fines de lucro dedicado a compartir ideas de expertos académicos.
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Rick Visser no recibe salario, ni ejerce labores de consultoría, ni posee acciones, ni recibe financiación de ninguna compañía u organización que pueda obtener beneficio de este artículo, y ha declarado carecer de vínculos relevantes más allá del cargo académico citado.
