Spring returns, the temperatures rise and like every year, right on time, they enter the scene, the so-called red spiders, those very small, bright red creatures that run quickly over bricks and railings. At the sight of which, often, the first reaction focuses on sprays and cleaning. Well, don’t do it, because it would be a serious mistake, both practical and biological.
They are not spiders, nor parasites
The first misunderstanding to clarify concerns the identity of these animals, because they are not spiders, but arachnid mites: the most widespread species on the walls of our homes is the Balaustium murorumwhose Latin name already describes the preferred habitat.
The intense red color is not accidental, it depends on the hemolymph, rich in carotenoids, which acts as an evolutionary warning signal, the so-called aposematism, to dissuade predators. Furthermore, the main natural enemies of these mites do not have photoreceptors to perceive red, which makes them effectively invisible to the predators themselves.
Be careful not to confuse them with the Tetranychus urticae (we can see it in the image below) the red spider that attacks garden and house plants: that is a parasite, it has completely different habits and has nothing to do with the species that colonize balconies and walls.
Because they arrive in spring
The appearance between April and June responds to a precise biological cycle, which sees us spend the cold months in a state of quiescence, and then come out to absorb the heat. These mites come out to absorb heat (brick and concrete heat up quickly and offer the ideal habitat, which is why we always see them on external walls and balconies). The cracks in the plaster provide shelter for the eggs, which need high temperatures to hatch.
Then there is the question of food, given that the Balaustium murorum it does not touch plants, its diet includes harmful insect larvae and, rather efficiently, guano and bird droppings that accumulate on ledges and railings. In fact it acts like a microscopic scavenger, carrying out a job that no pesticide could do with equal precision.
Why insecticides are useless (and counterproductive)
Here the second most frequent mistake comes into play, that is, resorting to common insecticides. Since these animals are mites and not insects, normal supermarket products have no effect on them. The only result is polluting your balcony, breathing in chemicals and staining your walls — for nothing.
The only concrete inconvenience of red spiders concerns laundry, because if inadvertently crushed, they would release hemolymph, a substance that persistently stains light fabrics. Otherwise they are completely harmless, given that they do not sting, do not bite, do not transmit diseases and are harmless to pets.
How to drive them away without killing them
The simplest solution is patience, given that the arrival of the summer heat means farewell: the spiders will leave on their own to hibernate until the following spring. Anyone wishing to discourage them without resorting to poisons can try natural remedies, for example you could place expanded clay in saucers, which would create a humid microclimate unwelcome to our mites, or use a solution of Marseille soap diluted in water, to be sprayed on walls and windowsills, which would act as a repellent. Rosemary, mint and lavender essential oils can also keep them away.
None of these solutions are definitive, nor should they be, because the presence and continuous return of these mites is part of a balance that, even in the small of a balcony or an urban garden, works and should not be interrupted. Taking them off the chain doesn’t really help anyone.
