When the bats are not there, the mosquitoes dance

To hear from many people, you would swear that mosquitoes have never been as abundant as this summer. But what could be the cause of such a great abundance of critters? It is certain that the torrential rains of August allowed mosquitoes to breed happily because their larvae develop in stagnant water.

However, the hot and humid climate of the summer that we have just experienced does not alone explain this increase in mosquitoes. The dramatic decline in populations of certain insectivorous animals, such as swallows and bats, is also to blame.

All bat species recorded in Canada feed on insects, many of which are harmful, such as flies and mosquitoes. For example, a single little brown bat can eat a quantity of insects equivalent to its own weight in a single night! They also attack insects that ravage crops, such as the cucumber beetle.

Like certain species of birds, bats are currently experiencing a spectacular decline because they unfortunately face various threats such as climate change, habitat loss, accidents involving wind turbines and, above all, the white-nose syndrome, a fatal fungal disease. Some North American bat populations have declined by 95% since the appearance of this terrible disease. It is estimated that nearly 7 million bats have died since the disease was introduced to North America.

White-nose syndrome appeared in the United States in 2006. The fungus responsible for this disease, called Geomyces destructanswas probably introduced into a cave in the Albany, New York area by explorers or cavers who carried dirt from European caves on their equipment. Unlike European bats which seem rather resistant to this fungus, North American species are very sensitive to it, particularly the little brown bat, the eastern pipistrelle and the northern bat. Since no effective treatment for white-nose syndrome has been discovered to date, some experts believe that the little brown bat will disappear completely from many regions of Canada.

Bats are fascinating animals with amazing abilities. Of all mammals, bats are the only ones that can truly fly. Their hands have long bones covered with a membrane that acts as wings. Bats typically rest hanging by their legs, upside down.

Bats have the ability to orient themselves and hunt their prey in the dark. They do this using an echolocation system, similar to sonar. Bats emit sounds and, if they hit an obstacle or object, they pick them up, allowing them to judge distance and format. Bats use high frequency sounds varying between 40 and 100 kilohertz. Because the human ear only detects sounds with a frequency below about 20 kHz, unfortunately we cannot hear them.

Help bats by installing a nest box

Unlike pollinating insects and birds, it is rather difficult to attract bats to a garden. The presence of a watercourse, where many mosquitoes will develop and be born, near your land is certainly an important asset. On the other hand, as bats mainly eat insects, the majority of plants emitting scent and nectar at night – the hosta plantain, for example – on which the insects feed will thereby attract these flying mammals. .

During the day, bats need a very warm place to take refuge and raise their young in peace. This resting place can be a hollow in a rock or a cavity in a tree. It is also possible to buy or make yourself a nest box specially designed to accommodate small colonies of bats and thus contribute to the conservation of these mammals.

Make sure the birdhouse you buy or make has the following features:

– It has a height of at least 60 cm.

– It is equipped with a vertical board which extends beyond the base of the nest box by 7.5 cm to 15 cm to facilitate entry to the dormitory. This board must be made of raw wood, not planed or marked with grooves spaced 0.5 cm to 1 cm apart.

– It has one to four interior partitions. These must have a height of at least 50 cm and a width of at least 35 cm.

– As bats need a rough surface to cling to, interior partitions should be made with raw, unplaned wood. You can also make several grooves there.

– The exterior of the nest box must be perfectly waterproof and not allow water or light to penetrate.

– It should be dark in color to better absorb heat, so that the temperature inside the dormitory is between 27^oC and 37^oC.

The best location for a bat box is near a pond, marsh, small lake or quiet river. Most North American bat species prefer to live in a roost located less than 300 meters from a watercourse in order to drink there and chase away mosquitoes and other insects that they eat. nourish. Also make sure your nest box is placed facing south, exposed to full sun and clearly visible. A shelter installed on a building or post is easier to spot than a nest box installed in the canopy of a tree. The occupancy rate and colonization speed are generally much higher for nest boxes hung on human constructions.

Place your bat box more than four meters off the ground so that it is not accessible to cats or other animals. In addition, it is strongly recommended not to place the nest box too close to balconies, galleries, patios, terraces and parking lots as well as windows and doors of your residence, as bat urine can stain certain materials. The majority of nest boxes have a downward opening which prevents the accumulation of droppings inside. These will therefore accumulate on the ground, under the nest box. Bat droppings, called “guano,” are very rich in nitrogen and make an excellent fertilizer for ornamental plants grown for their foliage.

Inside the nest box, the temperature should ideally be between 27^oC and 37^oC. The big brown bat prefers a temperature below 35^oC, while others, like the little brown bat, tolerate temperatures above 37^oC. The interior temperature of the nest box is directly influenced by the type and color of the exterior covering as well as its orientation. A dark coating and a south-facing orientation help maintain an ideal internal temperature. You will probably need to do a few experiments before you get the right location and ideal temperature. You can use a thermometer with a probe that can be placed inside the nest box.

Bats like their roost to be clean. You must therefore maintain their nest box if you want them to return year after year. Inspect your nest box every month to ensure their presence and the absence of problems such as the presence of predators, too low or too high a temperature, water infiltration, etc. Also be sure to remove any debris as well as wasp, bee or bird nests if there are any. However, any repairs as well as cleaning must be done when bats are absent.