Aotearoa Science Agency
Entomologist Fiona Cross, aka “Dr Aranha”
Your home could have dozens of spiders — or many, many more than that. The good news: Our homes provide little food for spiders. The bad news: they don’t have any of their predators either. But don’t worry, you can sleep peacefully…
How many spiders are in your house? Pest control companies often point to a number on the order of 40 spiders in an “average” housebut it is difficult to find, in the published scientific literature, anything that directly supports this estimate.
One in 2016, carried out in 50 homes in North Carolina, USA, found irregular web spiders, arachnids from the theridiid family, in 65% of all rooms analyzed. But the aim of the study was to assess biodiversity and not to count the number of individual spiders…
Thus, if a typical house has five or six divisionsin addition to corridors, according to the estimate found in the 2016 study, the average would be somewhere around the 10 spiders per roomwhich already seems like a lot.
To answer a recent question from readers on , the zoologist Luis Villazon did an “investigation” on his own: he vacuumed the entire house (a rare event) and found only 26 spiders. But this only corresponds to the areas of the house that we can observe relatively easily.
If we consider what is under the floor, behind the refrigerator, in the attic, in the garage and so on, it is entirely possible that there is as many or even more hiding, notes Villazon.
If we look at the average density of spiders outdoorswe can take as a basis a frequently cited value, from one published in 2017, of 131 spiders per m² of land, which is equivalent to an order of magnitude of around 10 quadrillion spiders worldwide, or one million spiders per human.
A typical house actually has relatively little food for spiders. But there is also almost none of the top predators of a spider, such as centipedes and birds, so each spider can live longer indoors than outdoors.
Furthermore, spiders put between 10 and 250 eggs at a timeand can produce up to five postures per year. Less than 1% will reach adulthood, but even so, if we include baby spiders in the household population “census”, the number can reach, at any time, a few thousand spiders.
Now the good news
Don’t worry, and sleep peacefully. The spiders at home are not exactly tarantulas, or black widows. Although some have poison, this is too weak to harm humans. In fact, spider bites are much rarer than we think.
Furthermore, if you happen to find one or two spiders at home, scientists — firstly because, like us, they are organisms with the right to life.
But more importantly, killing a spider eliminates an important element of balance within homes. Spiders are generalist predators that eat various types of insects, helping to eliminate uncomfortable prayers and disease-carrying creatures, such as mosquitoes… and other spiders.
