It is no coincidence that spiders are a symbol of Halloween: in autumn it is much easier to see spiders in our homes. The most obvious explanation is that this greater presence is due to seasonal temperature drop: Spiders, looking for a warmer shelter, but also for food and moisture, enter homes from the outside in early autumn. In reality, things are not quite like this: outdoor-adapted species that seek shelter in homes are very few and do so rarely. What we observe instead is a increase in activities of house spider species already present in our homes. The end of summer and the beginning of autumn, in fact, coincide with the breeding season of these species: spiders, especially males, become less shy and more competitive looking for a mate with whom to mate, and it is thus much easier to see them out in the open.
The breeding season makes spiders more enterprising
The end of summer and the beginning of autumn coincides with the takeover of breeding season of many species of spiders, not just domestic ones. Most spiders are solitary and seeks company only during the reproductive period. While the females remain hidden, the males increase their activity and leave their usual refuges, searching for females to mate with. They become resourceful even during daylight hours, when they would normally stay hidden, ed it is for this reason that we notice them more easily in autumn.
This is also the time of year when males reach their larger size, becoming even easier to see; furthermore, the competition between males hunting for a partner causes the larger ones to chase the smaller ones away from their usual shelters, sending them wandering out into the open. It is therefore not the number of spiders that increases, but their activity.
Domestic species of spiders live on average only one year: in the case of Tegenaria or Eratigena, after fertilization, the female wraps around seventy eggs in a protective sac in a safe place: they will hatch after a couple of months, dispersing in search of a new refuge to colonize.
Seeing more spiders in autumn is therefore not a sign of intruders from outside or of some type of infestation, but rather a natural consequence of their life cycle and seasonal habits. The presence of spiders in the house is one of the most natural ways to avoid a possible infestation of other invertebrates potentially more annoying: spiders offer a fundamental ecosystem service to our species, reducing both the number of flies, cockroaches etc. inside homes, and that of aphids, caterpillars and other pests in greenhouses and cultivated fields. In Italy, only two of these spiders, the violin spider and the malmignatta, have a bite of medical relevance for us humans, while the rest of the species are for us harmless.
The most common spider species: “garden” and “house” spiders
Even if it’s about species “synanthropic“, that is, those that live in close proximity to human beings, spiders that live outside of houses and those that make their lair within the home tend to be distinct from each other. Typical species of gardens, walls and other external environments close to houses, like the cross spider (Araneus diadematus), the wasp spider (Argiope bruennichi) or the numerous species of small jumping spiders (family Salticidae) are well adapted to survive external conditions. They weave large webs between one plant and another with which they capture passing prey or, as in the case of Salticids, jump on small invertebrates on leaves and external walls. When the temperature drops too much, their activity is reduced and they go into one state of dormancy producing “antifreeze” compounds in their body that lower the freezing threshold. At the same time, spiders tend to be attracted to heat, which helps regulate their body temperature, therefore it rarely happens that any of these species sneak into your home with the arrival of autumn, perhaps through a still open window.
Domestic spider species, however, they are in our house all year round: the Tegenaria domesticathe Eratigena atricathe pholcid spiders (family Pholcidae) or the violin spider (Loxosceles rufescens) nest in the corners of walls, or in crevices, attics and other dark, damp corners. Contrary to outdoor species, these spiders they prefer the conditions of the domestic environmentinside which they hunt flies and midges, silverfish and other smaller spiders. They venture out of the house very rarely, and usually only to move from one indoor environment to another. A few species, such as the wolf spider (Hogna radiata) are well adapted to both the external and internal environments.
