Up close, a bat is a furry mammal that flies on its hands, with a thin sheet of skin stretched between hugely long fingers. Most of what looks strange about it, from leaf-shaped noses to oversized ears, is gear for flying and hunting in the dark. There is no single bat look, though, because body shapes shift with what each kind eats and how it finds food.
The Basic Body Plan of a Bat
A bat’s arm and hand bones are much longer than those of a land mammal its size.1PubMed. Biomechanics of the bat limb skeleton: scaling, material properties and mechanics They are also thicker, while its leg bones are noticeably thinner.2PubMed. Biomechanics of the bat limb skeleton: scaling, material properties and mechanics
The chest is built much like a flying bird’s. Bats have a ridge on the breastbone where big chest muscles attach,3PubMed Central. Evolution of Flight Muscle Contractility and Energetic Efficiency and the main one pulls the wings down on each beat.4PubMed Central. What Factors Shape the Flyability in Bats?—The Perspective from Bat’s Wing Development The heart is large for a mammal, about 1% of body weight and up to 2% in some bats.5IntechOpen. Biomechanical, Respiratory and Cardiovascular Adaptations of Bats and the Case of the Small Community of Bats in Chile
A resting bat looks like a furry body wrapped in folded, leathery wings, which hide how long the fingers really are. Most bats are small enough to fit in a hand, though flying foxes are much larger.
A roosting bat shows bare, dark wing skin, large ears, and often a pug-like or pointed face. A small clawed thumb pokes out from the front edge of the wing.
How a Bat’s Wing Is Built
The wing is really a hand. Four very long fingers spread the skin like the spokes of an umbrella, while the thumb stays short and clawed, free of the membrane. Finger proportions track lifestyle: bats that hunt in open air tend to have a longer third finger and a shorter fifth finger, while bats that pick food off leaves in cluttered places have the opposite build.6PubMed Central. Ecological Morphology of Neotropical Bat Wing Structures
The bones inside are made to bend. Wing bones carry less mineral than other mammal bones, and less still toward the wingtip.7PubMed. Biomechanics of the bat limb skeleton: scaling, material properties and mechanics That makes the outer wing more flexible, which helps it give during flight.
Compared with a bird’s wing, which is feathers on a mostly fused hand, a bat’s is skin on a spread hand. A torn membrane can heal, while a bird has to regrow feathers.
Because the skin attaches to the finger bones, a bat can reshape the wing by moving its fingers. It can spread or draw in its fingers to change the wing’s curve and area, broad for slow, tight turns and narrower for speed. On the upstroke it typically folds the wing in somewhat to cut drag, so the wing is not held fully open through every beat.
Up close, the skin is thin and stretchy, often nearly see-through against a light. Fine blood vessels and fibers cross the membrane. The skin is also dotted with tiny hairs on both top and bottom,8PubMed. Morphology and deflection properties of bat wing sensory hairs: scanning electron microscopy, laser scanning vibrometry, and mechanics model too small to notice without magnification. These hairs connect to touch sensors and likely help bats feel airflow while flying.9PubMed. Hair, there and everywhere: A comparison of bat wing sensory hair distribution10PubMed Central. Functional role of airflow-sensing hairs on the bat wing They are thicker near the body than near the wingtip.11PubMed. Hair, there and everywhere: A comparison of bat wing sensory hair distribution
At the back, many bats have a skin membrane stretched between the legs and tail.12PubMed Central. A Potential Role for Bat Tail Membranes in Flight Control A thin spur on the ankle helps support that membrane’s edge.13PubMed. Assessment of the Hindlimb Membrane Musculature of Bats: Implications for Active Control of the Calcar By moving the legs, a bat can tilt the tail membrane, which helps it pitch up and down sharply.14PubMed Central. A Potential Role for Bat Tail Membranes in Flight Control In some bats small muscles control the ankle spur, suggesting it aids quick turns.15PubMed. Assessment of the Hindlimb Membrane Musculature of Bats: Implications for Active Control of the Calcar
Why Some Bats Have Strange Noses and Big Ears
Many bats find food by echolocation: they make high-pitched calls and listen for the echoes to locate objects. Noses and ears are shaped to send those calls out and read what comes back. Bats that call through the mouth tend to have a skull tilted upward.16Discover Magazine. Echolocation Shapes a Bat’s Skull to Match Specific Frequencies Bats that call through the nose lack that tilt and have elaborate nose flaps and larger ear bones.17Discover Magazine. Echolocation Shapes a Bat’s Skull to Match Specific Frequencies Bats using higher-pitched calls tend to have shorter faces.18Discover Magazine. Echolocation Shapes a Bat’s Skull to Match Specific Frequencies
The calls start in the voice box, and the face then shapes how the sound leaves the head and how echoes arrive. Nose callers use the noseleaf, a leaf-shaped flap of skin around the nostrils,19Functional Ecology. Morphological diversity in the sensory system of phyllostomid bats: Implications for acoustic and dietary ecology something like a megaphone that shapes and directs the beam. Its shape is linked to the pitch range of the bat’s calls.20Functional Ecology. Morphological diversity in the sensory system of phyllostomid bats: Implications for acoustic and dietary ecology Some leaf-nosed bats narrow their sound beam as they close in on an object,21PubMed Central. Sonar beam dynamics in leaf-nosed bats and by tilting the flap, a bat may tell how high or low a target is.22PubMed. Bat noseleaf model: echolocation function, design considerations, and experimental verification Mouth callers often have simple noses, since nose flaps aren’t aiming their sound.
On real bats, horseshoe and leaf-nosed species carry fleshy flaps that look like small leaves or spears. Plain-faced bats have simple noses but often large, mobile ears, and long-eared bats can have ears nearly as long as their bodies.
Big ears collect more of the faint returning echo, which helps a bat hunting small prey in the dark. Their surfaces are often ridged, and the folds help shape how sound enters. Some bats swivel their ears, even independently, toward a sound. Some with huge ears fold them back or tuck them under a wing while sleeping, which is why a roosting bat’s ears can seem to vanish.
Many bats also have a small flap inside the ear, the tragus.23PubMed. Echolocation in bats: the external ear and perception of the vertical positions of targets It creates a second echo whose timing tells the bat a sound’s height.24PubMed. Echolocation in bats: the external ear and perception of the vertical positions of targets With the tragus bent aside, a bat’s sense of up-and-down worsens from about 3 degrees to about 12 to 14 degrees.25PubMed. Echolocation in bats: the external ear and perception of the vertical positions of targets
Are Bats Really Blind
No bat is blind. Flying foxes and other fruit bats have very large eyes,26Wildlife Online. Is the expression “blind as a bat” justified? because most don’t echolocate to find food and rely on sight instead.27Wildlife Online. Is the expression “blind as a bat” justified? Their brains have relatively large areas for controlling eye movement.28PubMed Central. Divergence of dim-light vision among bats (order: Chiroptera) as estimated by molecular and electrophysiological methods Big dark eyes and dog-like faces give flying foxes their name. Their ears are usually simpler and smaller.
Smaller echolocating bats usually have proportionally small eyes, often half hidden in fur.29Wildlife Online. Is the expression “blind as a bat” justified? Those eyes likely suit nearby, wide-focus vision rather than sharp detail.30Wildlife Online. Is the expression “blind as a bat” justified? Small is not useless, though. These bats can use sight, especially for seeing dim light and the horizon at dusk. Sight helps over longer distances, where echoes fade, while echoes handle close detail in darkness.
Vampire bats add a different sense. They have heat sensors on the nose that react to warmth around 30°C, near skin temperature.31PubMed Central. Ganglion-specific splicing of TRPV1 underlies infrared sensation in vampire bats They may sense a warm animal from about 16 cm away to pick a bite spot.32Journal of Comparative Physiology ? A. Thermoperception in the common vampire bat (Desmodus rotundus)
Teeth, Skulls and Tongues Shaped by Diet
Nectar-feeding bats have long, narrow skulls.33PubMed Central. Signatures of echolocation and dietary ecology in the adaptive evolution of skull shape in bats Skull shape has changed most often in the leaf-nosed bat family, which eats the widest range of foods.34PubMed Central. Signatures of echolocation and dietary ecology in the adaptive evolution of skull shape in bats Among insect eaters, bigger bats that eat tough beetles have blunter teeth and sturdier heads, while smaller bats eating soft insects have sharper, more complex teeth and lighter heads.35Functional Ecology. Craniodental traits predict feeding performance and dietary hardness in a community of Neotropical free‐tailed bats (Chiroptera: Molossidae)
Teeth are tools. Sharp cusps slice or pierce insect bodies, while flatter teeth crush fruit. Insect-eating bats often have many small pointed teeth that mesh like shears to cut through hard exoskeletons, and you can see them when a small bat opens its mouth to call. Nectar bats often have small, reduced teeth, since their food needs little chewing. Vampire bats don’t suck blood. Razor-sharp front teeth make a small cut, and the bat laps up the blood.
The extremes are striking. One bird-eating bat has a large, high skull, thick jaws and a strong bite.36PubMed Central. Correlation of skull morphology and bite force in a bird-eating bat (Ia io; Vespertilionidae) At the other end, nectar bats have a tongue tip covered in long hair-like bristles.37PubMed Central. Specialized bat tongue is a hemodynamic nectar mop During feeding, blood fills the tip, the bristles stand up, and nectar is mopped into the mouth.38PubMed Central. Specialized bat tongue is a hemodynamic nectar mop
How Bats Hang Upside Down
Many bats have a locking section in the tendons of their toes and thumb.39PubMed. Chiropteran tendon locking mechanism It works like a ratchet, holding grip with little muscle effort.40PubMed. Chiropteran tendon locking mechanism That is why a sleeping bat can hang for hours.
The feet themselves are small, with five toes and sharply curved claws. They face backward so a bat can grip a ceiling, and the knees bend backward compared with ours, which helps with hanging. The thin legs reflect that bats rarely walk.
When a bat lands, it grabs on with its toes and its weight pulls the tendons tight, locking the claws. To let go, it usually has to tense muscles or lift its weight off, so releasing takes effort while holding does not. Hanging also lets a bat drop straight into flight, which matters because many bats can’t easily take off from the ground.
Fur, Colors and Scent Glands
Over 80% of bat species are basically one color all over.41Synapsida. Bats Can Be Colourful, Too Among the minority that are marked, the largest families show more patterns.42Synapsida. Bats Can Be Colourful, Too Some tent-making bats have bright yellow skin, and the Honduran white bat stores yellow pigment from plants.43Journal of Zoological Systematics and Evolutionary Research. Tent‐roosting may have driven the evolution of yellow skin coloration in Stenodermatinae bats Typical colors are brown, gray, black or reddish, and some bats have white tufts or stripes on the face.
The fur is thick and soft on the body, which helps insulate a small animal that loses heat quickly. Hair often looks banded or frosted, because individual hairs can have lighter tips or darker bases. Wing and tail skin are mostly bare, so they lose heat but can be tucked in at rest. Young bats are often duller or grayer than adults, and color can change with age.
Many male bats have scent glands on the throat, shoulders or wings.44Canadian Journal of Zoology. A histological examination of the holding sacs and glandular scent organs of some bat species (Emballonuridae, Hipposideridae, Phyllostomidae, Vespertilionidae, and Molossidae) These glands are small or absent in females.45Journal of Graduate Studies, York University. A Comparative Histological Examination of Scent Glands in Selected Chiroptera Some males have special larger hairs that hold and spread the scent.46Canadian Journal of Zoology. A histological examination of the holding sacs and glandular scent organs of some bat species (Emballonuridae, Hipposideridae, Phyllostomidae, Vespertilionidae, and Molossidae)
Why Bats Come in So Many Shapes and Sizes
In general, wing bones grow in step with body weight across bat sizes.47The Journal of Experimental Biology. Scaling of wingbeat frequency with body mass in bats and limits to maximum bat size Fruit bats are the exception: their wingspan grows faster than their weight, giving bigger ones longer, narrower wings.48The Journal of Experimental Biology. The effect of body size on the wing movements of pteropodid bats, with insights into thrust and lift production Large flying foxes therefore have long wings that suit efficient flight.
Scale shapes the body in other ways. Very small bats often have short, broad wings that suit maneuvering around obstacles, and wing size relates to what a bat eats and where it flies. That is why fast open-air hunters and slow forest feeders look different even at similar weights. Smaller bats also lose heat faster, one reason small species tend to shelter in warm, protected roosts.
Early bats looked different from today’s. One of the oldest known bats, from about 52 million years ago, weighed about 40 grams.49PubMed Central. Aerodynamic reconstruction of the primitive fossil bat Onychonycteris finneyi (Mammalia: Chiroptera) It had claws on all fingers and could likely climb well.50PubMed. Primitive Early Eocene bat from Wyoming and the evolution of flight and echolocation It could fly but likely could not echolocate.51PubMed. Primitive Early Eocene bat from Wyoming and the evolution of flight and echolocation The wing came first, and the sound-sensing face came later.