Of the 35,000 species of spiders described worldwide (out of an estimated 170,000 species), only a handful are considered to be dangerous and only 27 are known to have caused human fatalities.
Though most people have a big fear of spiders, it seems that venomous spiders are not such a big threat to humans as many people believe.
First of all, studies have shown that most serious bites attributed to spiders were, in fact, due to other causes, notably other arthropods.
There are, however, a few exceptions, and bites from certain species can cause severe dermatological lesions and other symptoms which require urgent medical treatment and care.
In Europe, like elsewhere in the world, spiders seem to strike fear into people more than any other creature, despite the fact that very few of the spiders found in Europe can really be considered dangerous to man.
Most venomous spiders in Europe belong to the Theridiidae family.
1. Comb-footed Spiders (family Theridiidae )
This is a very large family with over 300 described species in Europe in 38 genera.
These spiders live on dry rocky walls, or on the walls of houses or sheds. They usually build non-sticking, three-dimensional, often tangled and grubby webs and hide inside. A few species don't make webs at all, though.
1.1 Widow Spiders, Malmignatte (Latrodectus)
These spiders measure roughly 10 mm for the female, and hardly 3 mm for the male. Female mature over a period of 4-8 month and males in a 2-3 month only. The female can live up to three years and males only 6 months.
Widow spiders build their webs in dark places near the ground, preferring the sheltered sides of buildings, abandoned rodent holes, or openings in stone outcroppings. Though they rarely venture indoors, they sometimes make a home in outbuildings such as woodsheds or outdoor toilets. The web has a distinctive tangled appearance, and a series of vertical trap threads extending to the ground. Crawling insects get stuck on the sticky threads and are lifted into the web where the Widow Spider wrapped them in layers of silk, injects them with venom, and sucks them dry.
Young Widow Spiders leave the web and disperse by a process called "ballooning" whereby a thread line of silk is released until the drag of the air is strong enough to lift the young spider in the air.
- Latrodectus lilianae: found in the Iberian Peninsula
1.2 False Widows (Steatoda)
These spiders occur all over Europe (including England) and can be very abundant.
Males produce sounds during courtship by scraping their teeth on their abdomen against a file situated on the rear of the carapace.
False Widows are far less venomous than "real" Widows, though their bites might require medical attention. They are not thought to be aggressive, but bites can occur because they often live close (or in) to human habitations.
The European species in that genus are :
- Little White Spotted Malmignatte (Steatoda albomaculata)
This species occurs in Western Europe (from Denmark to Corsica...).
This beautiful, black spider displays paired spots on the abdomen and a narrow band around the front margin. The markings can be white, pale yellow or pink.
Steatoda albomaculata is usually found among stones or low vegetation in sand quarries, dry sandy pastures or heathers, especially on south facing slopes. It likes to build its web near a stone under which it can hide if disturbed.
- Coffee Bean Spider (Steatoda bipunctata):
This species is common throughout most of Europe.
It is dark brown to black rugose carapace with characteristic whitish markings along the mid-line and anterior edge of the abdomen, and reddish brown annulated legs with dark brown. Females measure 5-7 mm, and males 4.5-5.5 mm.
Steatoda bipunctata is commonly found in houses, but it also occurs in forests, usually under loose bark on tree trunks.
Other species are: Steatoda brignolii, Steatoda castanea, Steatoda distincta, Steatoda grossa, Steatoda incomposita, Steatoda italica, Steatoda latifasciata, Steatoda latrodectoides, Steatoda maura, Steatoda meridionalis, Steatoda nobilis, Steatoda paykulliana, Steatoda phalerata, Steatoda triangulosa.
1.3 House Spiders (Genus Parasteatoda and Cryptachaea, previously genus Achaearanea)
These spiders measure between 3 and 7 mm and have a distinctive abdomen which is much higher than wide, when seen sideways, and almost circular from above. Color varies greatly even within a species.
Parasteatoda and Cryptachae use a leaf hanging in the middle of their web like an inverted cone as a shelter from the rain or potential predators. Webs are often a bit messy with a certain amount of debris and wrapped insects.
Six species occur in Europe.
- Common House Spider (Parasteatoda tepidariorum)
It is a yellowish brown to dark brown spider with indistinct whitish chevrons and streaks on its abdomen, orange to reddish brown legs, and sometimes blackish markings in the center area of the dorsum. Females measure 5-7 mm, males 3-4.5 mm.
Parasteatoda tepidariorum often builds its web on the dry walls of buildings. Adults are found at all seasons.
- Parasteatoda lunata: from across Europe.
2. Recluse Spiders, Violin Spiders, Fiddleback Spiders (Loxosceles)
The approximately 100 described species of Loxosceles spiders don't generally occur in Europe, yet at least two species of those potentially dangerous spiders can be found in the Mediterranean region of southern Europe.
Loxosceles are six-eyed spiders, unlike most spiders that are eight-eyed. They measure roughly 9 mm in length and have long legs.
They are generally nocturnal and are known to live inside and outside buildings. Indoors, they often seek shelter in clothing, bed sheets and blankets, and are thus responsible for a number of bites.
The European species are thought to be less venomous than the feared American Brown Recluse spider.
- Loxosceles distincta: found in the Mediterranean region
3. Yellow Sac Spider, Long-legged Sac Spider (Cheiracanthium punctorium)
Family Miturgidae (previously Clubionidae )
Cheiracanthium punctorium is found from central Europe (including Germany, the Mediterranean region...) to Central Asia. It prefers fairly hot and arid areas.
It can measure up to 15 mm and, like other members of the Miturgidae family, it has a long first pair of legs and stout fang. Those fangs can penetrate the human skin causing a sharp pain that commonly last for twelve hours, and in some cases for as long as ten days.
Females build an egg sac of about 4 cm in high grass. It opens below and is aggressively defended.
Other mildly venomous spiders in Europe can be found in the Dysderidae family, Long-fanged Six-eyed Spiders (notably Dysdera crocata) and in the Lycosidae family, Wolf Spiders (notably Hogna radiata, and Lycosa oculata). However, none of these spiders are truly dangerous to humans.