The Vespertilio genus encompasses a group of bats recognized within the broader Vespertilionidae family, commonly known as vesper bats or frosted bats. This genus holds historical significance as the oldest accepted taxonomic name for bats, originally described by Carl Linnaeus in 1758. While once encompassing all bat species, its classification has since narrowed, yet it remains foundational to bat taxonomy. The name “vesper” itself derives from the Latin word for evening, reflecting the bats’ nocturnal activity.
Physical Characteristics of Vesper Bats
Bats within the Vespertilio genus are medium-sized, with a body length ranging from 4.8 to 6.4 centimeters (1.9 to 2.5 inches). Their wingspan extends between 26 and 33 centimeters (10 to 13 inches), and they weigh between 11 and 24 grams (0.39 to 0.85 ounces). A distinctive feature is their “frosted” fur, where the dorsal side exhibits a red to dark-brown coloration with silver-white tips on the hairs, creating a unique bicolored appearance. The ventral side, in contrast, is typically white or grey, contrasting with the darker back.
Their facial features include short, broad, and roundish ears, which, along with their wings and face, are black or dark brown. The wings are narrow, contributing to their flight characteristics. A short, broad tragus, an outgrowth from the base of the ear, is also present.
Habitat and Geographic Range
These bats exhibit a wide geographic distribution, primarily inhabiting temperate regions across Eurasia. Their range extends from Western and Southern Europe eastward, covering areas such as the Caucasus, Iran, Mongolia, northeast China, Korea, Afghanistan, and northern Pakistan. They naturally occur in diverse environments including mountainous terrain, steppes, and forested areas. However, their ecology also includes a synanthropic tendency, often living in close association with human-made structures.
In Western Europe, for example, they are frequently found in urban settings. This allows them to utilize tall buildings, bridges, and barns as roosting sites. Some populations have been recorded at high altitudes, reaching up to 3,400 meters above sea level in mountainous regions.
Diet and Foraging Habits
Frosted bats are insectivores, primarily feeding on flying insects. Common prey items include moths, flies (Diptera), caddis flies, beetles, and aphids. These bats forage after twilight, hunting in open areas. They fly at heights of 10 to 40 meters (33 to 131 feet) above ground, over water bodies, meadows, open landscapes, or even near street lights where insects congregate.
They employ echolocation to locate and track their prey in the dark. This involves emitting ultrasonic calls at frequencies of 22 to 29 kHz. By interpreting the echoes of these sounds, they construct a detailed acoustic map of their surroundings, enabling them to capture insects efficiently. Prey is caught in mid-air, sometimes scooped directly into their tail or wing membranes during flight.
Reproduction and Hibernation
Frosted bats mate in late autumn, during October and November. During this period, males emit distinct, audible mating calls, often observed near tall buildings or cliffs, which may also serve as potential hibernation sites. Females form maternity roosts from May to July, where they gather to give birth and raise their young. These nursery colonies can range in size from 20 to 60 individuals, though some larger groups may include up to 200 females.
Pups are born in May or June, with females commonly giving birth to twins, and occasionally one or three offspring. The young are weaned in less than six weeks, after which the females disperse from the maternity roosts. As a migratory species, these bats undertake long-distance seasonal movements, with recorded flights up to 1,780 kilometers (1,110 miles). They hibernate between October and March, often alone, in sheltered locations such as caves, tunnels, underground structures, or undisturbed parts of high buildings, and can endure temperatures as low as -5 °C (23 °F).