Geoffroy's Bat

Fascinating facts about the Geoffroy's Bat

• A bat that hunts by listening to the rustle of spider silk: Geoffroy's bat can detect vibrations as faint as 0.1 millimetres — the thickness of a human hair — plucking spiders and insects directly off leaves and branches without breaking stride. Most bats use echolocation to catch flying prey; Geoffroy's bat silent-hunted, its ears tuned to the whisper of a web being plucked. This hunting style explains why it hunts low, close to vegetation, where the background noise of echolocation would be useless anyway.
• Their ears are notched in a pattern so distinctive that taxonomists named the whole species after it: 'emarginatus' means 'having a notch,' and the deep notch carved into the edge of each ear is so unusual it looks like someone took scissors to them. That notch isn't cosmetic — it's an acoustic funnel that helps them pinpoint the exact location of prey on a surface, a precision most echolocating bats cannot match.
• These bats roost in colonies of hundreds in caves and mines across Europe, but vanish entirely for weeks at a time: researchers have tracked Geoffroy's bat moving between summer and autumn roosts more than 200 kilometres apart, a journey that would take nights of travel for an animal the size of a thumb. The reason for these migrations remains partly mysterious — they seem to be searching for specific caves with particular temperature and humidity profiles, suggesting a level of environmental pickiness rare among bats.
• A female gives birth to twins — almost always — making Geoffroy's bat one of the few European bat species where reproduction is locked into a nearly fixed pattern: 96% of pregnancies result in two pups, born in June or July after a gestation of 50 days. This reproductive rigidity means populations grow slowly and make poor recovery from disease outbreaks, which is why white-nose syndrome, a fungal plague that kills hibernating bats, poses a real threat.
• They can survive winter by slowing their metabolism to a fraction of normal: during hibernation, their heart rate drops from roughly 800 beats per minute to just 10, and their body temperature plummets to match the cave around them. A bat can lose up to 30% of its body weight over winter and still wake in spring to hunt again, relying on fat reserves built during a brief autumn feeding window when insects are abundant.

At a glance

About the Geoffroy's Bat

In the warm, golden light of dusk, Geoffroy's Bat stirs, unfolding its delicate wings like a dark, leathery cloak, as it takes to the evening skies with a soft, whispery flutter. With an effortless, aerial dance, it weaves through the shadows, its large, round ears twitching with every faint echo, guiding it through the hunt for insects with unerring precision. As it flits and darts, its tiny, mouse-like face set in a fierce, intent gaze, this diminutive creature is a marvel of nocturnal adaptation, a master of the hidden world that comes alive beneath the stars.

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