Here in eastern North America we’re gaining a new appreciation for bats, not just as Halloween symbols but as insectivores, because several of our species are threatened with extinction due to white nose syndrome. The bats most at risk are those that roost in caves where cool moist temperatures allow the Pseudogymnoascus destructans fungus to grow and infect them.
Spix’s disk-winged bat (Thyroptera tricolor) is far removed from this danger because he lives in the tropics and roosts inside curled leaves. He recently made news in the journal Nature because scientists discovered he uses the curled leaves as an ear trumpet.
Leaf roosting has made him unusual in other ways, too. Most bats roost head-down but this species roosts head-up so it can exit the leaves quickly. Leaves are smooth and slippery so the bat has evolved suction cups on his wings and feet. These cups look like disks, hence his name.
Above, the bat is showing off his wing disks but his arms look really weird and stubby. To understand this it helps to know a little about bat-wing anatomy.
Bats’ wings are made of skin stretched from their armpits to their fingertips. Their four fingers, encased in thin skin, have evolved to be very long to give the wings their breadth. Bats’ thumbs, however, are not inside their wings and their thumbs are short.
In the photo above you can see the attic bats’ long fingers. The joint of the wing is at the bat’s hand/wrist. I’ve circled the tiny thumb. This one has a claw but Spix’s disk-winged bats have a suction-cup there instead.
When bats roost, they close their fingers to fold their wings. Most bats grab a perch with their feet but Spix’s uses suction cups to latch onto the inside of the leaf.
Suction cups on his feet alone are not enough. This bat is hanging on by his thumbs.
(photo of a Spix’s disk-winged bat taken near Golfo Ducle, Costa Rica by Alan Wolf. Bat wing from Wikimedia Commons. Click on each photo to see the original.)
p.s. Thanks to Peter Bell for alerting me to this fascinating bat.