Why do snails cluster in summer on top of plants and fence posts? We will try to explain it to you below.
Our land snails are mainly nocturnal, since at night the presence of predators decreases and the environmental conditions are more conducive to them, by significantly increasing the humidity of the environment. During the favorable time of the year, with mild temperatures and adequate environmental humidity, land snails feed in the herbaceous layer closest to the ground, being able to remain active for a good part of the day as well.
But when spring gives way to summer, temperature increases and the humidity of their environment decreases, producing a truly hostile environment to them. At this time of year they can’t even count on the help of the morning dew to ease their water stress. Their predominantly light-colored shells, typical of hot places, are no longer helpful either. To overcome these unfavorable conditions, which usually begin in June, land snails enter a state of dormancy in which their metabolism and pulsations are reduced to a minimum. Many animals employ this strategy in our hemisphere to withstand harsh winter conditions, but in the case of our land snails, they do so to survive the rigors of summer. It is therefore the equivalent of hibernation during the summer, so we can call it aestivation.
To do this, snails close their shell with a lid formed by a sticky calcareous secretion called epiphragm, which also stick them to the chosen substrate, be it a plant, a tree branch or a fence post. This mucous secretion solidifies on contact with air, hardens and closes the shell almost hermetically, although it leaves a small hole open to allow oxygen exchange.
Temperatures in summer decrease as we move away from the ground, heated by the sun’s rays, which is why the snails tend to climb up as much as possible. In addition, this way they cool off with the breezes that may blow during the day. This also keeps them away from some ground predators such as some myriapods and beetles, lizards, toads, rodents, hedgehogs and dormouses; although it exposes them to others such as birds (storks, egrets, blackbirds, little owls, kestrels, black birds and crested larks). But the number of snails is so high that these losses are perfectly assumed by the population.
The period of time that they may need to be lethargic can go from just a few weeks to several months, as occurs in our latitudes, where the dry season can last from June to October.
Sometimes, in favorable areas where they grow in large numbers, concentrations of several hundred of them can be observed, turning each fence post into an authentic living sculpture.