Greater Mouse-Eared Bat

The Greater Mouse‑eared Bat (Myotis myotis) is a medium‑sized vesper bat belonging to the family Vespertilionidae within the order Chiroptera. It inhabits a broad Palearctic range, extending from the British Isles and Scandinavia across Central and Eastern Europe, through the Caucasus and the Middle East, into Central Asia, and down to the northern fringes of Africa (Morocco, Algeria, Tunisia). The species prefers temperate deciduous and mixed forests, but it also occupies mountainous woodlands, river valleys, and semi‑arid scrub. Roost sites are typically caves, old mines, rock crevices, and occasionally buildings such as attics and barns. Adults weigh 9–16 g, measure 4.5–5.5 cm in head‑body length, and display the characteristic large, rounded ears that give the bat its common name. Its fur is brown‑gray on the dorsal side and paler ventrally. Myotis myotis employs frequency‑modulated echolocation calls (≈ 30–50 kHz) to navigate and hunt insects in open air and near vegetation. The species is listed as Least Concern on the IUCN Red List due to its wide distribution and large, apparently stable population, although local declines have been recorded where roost disturbance or intensive pesticide use occurs.

Greater Mouse‑eared Bats are highly social and form colonies that can range from a few dozen to several hundred individuals, especially during the maternity period. They are strictly nocturnal, leaving their roosts at dusk to forage for insects over forest edges, clearings, and water bodies. Individuals maintain relatively small home ranges, typically 2–5 km², and exhibit fidelity to both foraging grounds and roost sites. Communication relies on a sophisticated repertoire of ultrasonic echolocation pulses for navigation and prey detection, complemented by low‑frequency social calls used in mother‑pup recognition and colony cohesion. Seasonal movements are modest; in colder regions bats may enter torpor or hibernate in deep caves during winter, while in milder areas they remain active year‑round. Territorial aggression is limited, with competition mainly expressed through acoustic signaling rather than physical confrontations.

The Greater Mouse‑eared Bat is an insectivore that exploits a diverse assemblage of nocturnal arthropods. Stomach‑content analyses across its range have identified moths (Lepidoptera) as the primary prey, comprising 45–60 % of diet by volume, followed by beetles (Coleoptera), flies (Diptera), and occasionally spiders (Araneae). In agricultural landscapes, the bat consumes significant numbers of pest species such as the European corn borer (Ostrinia nubilalis) and the cotton bollworm (Helicoverpa armigera), contributing to natural pest control. Foraging is conducted primarily by aerial hawking—capturing insects in flight using agile, maneuverable flight—and by gleaning insects from foliage or water surfaces. Individuals can consume up to 4 g of insects per night, equivalent to roughly 30 % of their body mass, and may drink water directly from surface tension on leaves or from puddles.

Myotis myotis reaches sexual maturity at 12–18 months for both sexes. Breeding commences in late spring (April–June) when females form maternity colonies in warm, humid roosts. After a gestation period of 50–60 days, females typically give birth to a single pup, though twins occur in up to 10 % of litters in northern populations. Newborns weigh about 1.5 g and are altricial, relying entirely on maternal milk for the first three weeks. The mother visits the pup nightly to nurse while the rest of the colony provides thermoregulatory benefits. Weaning is completed by 4–5 weeks, after which juveniles join nightly foraging flights and gradually acquire hunting proficiency. Females may breed again the following year, but most individuals reproduce only once per annum.

The IUCN classifies Myotis myotis as Least Concern, reflecting its extensive distribution and large, stable population estimated at several million individuals. Nevertheless, the species faces localized threats that can cause colony declines. Disturbance or destruction of roost sites—through cave tourism, mining, demolition of old buildings, or forestry activities—removes essential maternity and hibernation habitats. Intensive pesticide use reduces prey availability and can lead to bioaccumulation of toxic compounds in bat tissues. Climate change may alter insect phenology and winter hibernation conditions, increasing mortality during extreme cold spells. Conservation actions include protecting key roosts, enforcing cave access regulations, promoting bat‑friendly building renovations, and monitoring pesticide residues in foraging habitats. Population trends remain generally stable, but long‑term monitoring is recommended to detect subtle declines.

• The species can enter deep torpor, lowering its body temperature close to ambient during cold spells.
• Greater Mouse‑eared Bats have one of the most diverse diets among European bats, preying on over 200 insect species.
• Their echolocation calls are highly adaptable, shifting frequency to reduce interference in cluttered habitats.
• Females can delay fertilization by storing sperm over winter, timing birth to the spring insect surge.
• In some regions, they are known to roost in historic churches and castles, sharing space with humans for centuries.