Winter is a period of “respite” for those who can’t stand insects, given that in our latitudes most species go into diapause in this period; However, it is easy to find another group of Arthropods in your home even in winter: spiders. Different genera, belonging to 7 families, usually live and complete their life cycle in homes and for this reason they are defined “house spiders”. In the house they find ideal conditions as they are attracted to moisture, heat, lack of natural predators and prey to catch.
Even if not everyone likes their presence, spiders are excellent “domestic collaborators” considering that they keep homes clean eliminating a variety of insects that they feed on: aphids, cockroaches, silverfish, flies and especially mosquitoes. They are not vectors of diseases and even the silk of the house spider (Tegenaria domestica) It has antibacterial properties on Gram positive bacteria. The species present in Italy are not poisonous to humans, except in certain situations for the violin spider (Loxosceles rufescens), which is the only species of domestic spider in Italy dangerous to humans. So, why kill them or drive them away, unless you are arachnophobic? In this case, some essences and specific repellent paints with controversial effectiveness seem to be useful.
How house spiders behave and where they are found
Some species can be defined as “domestic” precisely because they now find in our homes the most suitable environment for survival and reproduction: these are species that in nature occupy the bark and cracks of trees, ravines or cavities among the rocks, but have now become synanthropic (i.e. they live close to humans). A study conducted in Belgium on 43 homes in some cities over the course of an entire year (from October 2014 to September 2015) made it possible to detect the presence of 93 species of spiders of which 19 are classified as real “house spiders”.
Even though they may be scary, most house spiders are actually our excellent allies: it has been calculated that a single spider can consume up to 2,000 insects in a year and some species are even specialized in feeding on the various developmental stages of mosquitoes, from eggs to adults.
Among the various rooms of the house, most of the specimens were found in the living room and bathroombut this is probably linked to the fact that in these environments people spend more time and look around noticing their presence. Males are seen out and about more than females, because the latter are generally less mobile. A numerical increase of specimens is noted in fall, starting in late September, as many large house spiders breed at this time of year. Furthermore, since they are not able to climb on smooth and slippery surfaces, males are often found in sinks and bathtubs intent on attempting to climb up from these surfaces, but also near windows, door keyholes or small cracks between the walls. Females generally stay closer to the webs in corners or on ceilings.
The most common species in homes
Among the domestic spiders present in Italy, only the Loxosceles rufescens (the violin spider) represents a danger to humans, while the others are not poisonous and they do not transmit diseases. Indeed, they could be a tool against some bacteria: the silk produced by Tegenaria domestica he showed in vitro specific growth inhibition activity of Gram positive bacterial strains! Below, we present some of the most frequent species in Italy.
- Dancing spider (Pholcus phalangioides)
According to the study conducted in Belgium, this is the most widespread species and was observed in two-thirds of the buildings. In fact, even in Italy and the rest of Europe the dancing spider is very common. To capture prey, it leans forward with its entire body, keeping only two of its eight long, thin legs anchored to the web, and then wraps them entirely in silk.
- Giant house spider (Tegenaria parietina)
A brown spider, somewhat impressive due to its size (body up to 20 mm long in females) and hairy legs, but absolutely harmless to humans. It builds large “sheet-like” webs with a fairly dense weave and complete with a tubular shelter in which the spider hides. The prey that ends up on the canvas comes paralyzed and then dragged into the funnel to be consumed.
- Spitting spider (Scytodes thoracica)
It is a not very large spider (body approximately 4-6 mm), with a characteristic contrasting hazel and black colour. It’s said spitter because it slowly approaches its prey and, at a certain distance, spits a sticky mixture that traps and immobilizes her. It then injects the poison into the victim’s body and feeds on it.
How to keep spiders away in the house: what to do
Since, all things considered, spiders are animals harmless for humans here in Italy, with the exception of the violin spider, and they are also quite useful as predators of weed species, it would be best not to eliminate them from homes. Unfortunately, however, not everyone appreciates them as roommates and therefore some precautions can be taken to keep them away. Given some “logistical” advice such as sealing any cracks or replacing broken mosquito nets, popular tradition sees vinegar and various natural essences as repellents for spiders. There are three active ingredients in particular – lemon essential oil, peppermint oil and chestnut fruits – tested on three species of spiders.
The research results have shown that chestnuts andmint essential oil had high efficacy on two species and moderate efficacy on the third, while the lemon one had no effect on any of these species. Some have even been tested repellent paints to be passed on the walls of houses to ward off certain species of the Loxosceles genus, but i Efficacy results are controversial. It is simply possible to eliminate the unfortunate ones with a vacuum cleaner, thus removing cobwebs and spiders.
