LAZZARO SPALLANZANI watched by the flickering light of a single candle as a bat flew hither and yon around his simple room in Reggio nell’Emilia, Italy. Then he made a remarkable observation: when he blew out the candle, the bat’s flight was unaffected. It flew in total darkness as if it were light! Spallanzani, an ordained Catholic priest and tireless, self-taught scientist, knew this because he had tied some string around one of the bat’s bony ankles. Holding tightly to it like a strange kite, he occasionally felt the bat tugging in different directions as it flew around in the pitch-black room. When he repeated the test with his tame barn owl – or “night-bird”, as he called it – the owl became clumsy in total darkness. It flew into the walls. It collided gracelessly with objects in the room.
How was the bat different to the owl? With this simple question in 1793, Spallanzani began an ingenious series of experiments that still hold up today – in terms of rigour, if not ethics. His studies might have been revolutionary, if everyone had known about them. Instead, most of the work went unpublished. It was sent in letters to correspondents. Other findings he committed to notebooks, unread until the 1940s. Instead, it would take another century and a half from the time of his discovery for researchers to uncover the complex system of echolocation that bats use to navigate.
Born in 1729, Spallanzani wrote widely about the natural world – about swallows, owls and eels. His interests seemed endless. He filled his notebooks with observations about reproduction, breathing and the maintenance of body temperature. He was widely known as an expert on sperm. In one study, he proved that sperm is involved in frog reproduction by dressing male frogs in tight taffeta pants to prevent its release. He was so industrious that his contemporaries called him Magnifico. And as you might expect from any historical figure with such a nickname, he was zealous. For example, to better understand digestion, he swallowed little food-filled cheesecloth bags tied to string and, at regular intervals, hauled them up from his stomach to assess their contents.
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Hello, flittermouse
But bats really fascinated him. żěè¶ĚĘÓƵs knew little about bats when Spallanzani had them flying around his room. In 1758, Carl Linnaeus had only named a handful of bat species in the definitive tenth edition of Systema Naturae, his attempt to classify the natural world. He was the first person to separate bats and birds taxonomically. Today, there are more than 1300 known species. Diverse and highly adapted, they are found on every continent except Antarctica. But in 1793, people still argued about whether bats had more in common with mice or birds. In the Roman era, Pliny had placed them with birds, an error with a long life. Linnaeus made the correction, but some ideas die slowly.
In Spallanzani’s day, bats were also known as flittermice. Some people thought the only thing a flittermouse was good for was curing gout and leprosy. As Zoologia Medicinalis Hibernica, a medical textbook published earlier that century, put it: “Bat, or Flittermouse, The flesh of a bat medicinally taken, is good against a scirrhus of the liver, the gout, rheumatism, cancer, and leprosy.”
But Spallanzani’s mind was alert to the simple mystery that eluded others. How does a bat navigate in the dark? At first, he approached the subject gently. He covered a bat’s head with a tiny, opaque hood. Suddenly, it flew into the walls of his room like the owl would in his later experiment. This led him to the logical, though mistaken, idea that somewhere that looked dark to humans and owls had some mysterious luminescence, which a bat with no hood could see. “Thus a place which we believe to be completely dark is not so at all,” he wrote.
“My astonishment at this bat, which can see without eyes, is inexpressible”
To test this hypothesis, he covered bats’ eyes with birdlime, a sticky substance that locals spread on trees to catch birds. This time, to his surprise, although the bats were effectively blinded, their navigation was unaffected. “These phenomena induced me to perform another experiment which I considered decisive,” wrote Spallanzani in August 1793, “namely to remove the eyes of a bat.” This excision duly done, he was stunned to find the bat could still navigate. “My astonishment at this bat, which absolutely could see although deprived of its eyes, is inexpressible,” Spallanzani wrote.
Around the same time, a researcher called Charles Jurine in Geneva, inspired by his correspondence with Spallanzani, was plugging bats’ ears with grease. He observed that their flight was impaired. It was becoming clear that the bats must be using their ears to find their way. Spallanzani’s hooded bats had been unable to hear properly; that they couldn’t see was less important. Ultimately, Spallanzani devised an elegant experiment to resolve the question once and for all. He made two small, cone-shaped tubes from brass and fixed them carefully in a bat’s ears. With the cones in place, the animal flew unaffected. “When I closed the tubes with pitch so that the air could no longer enter the auditory duct, the animal did not fly at all, or its flights were short and uncertain, and it frequently fell.”
In the summer of 1794, Spallanzani took his exploration of bats’ abilities to another level – literally. In the bell tower of the cathedral in Pavia, he swept a net through the air, retrieving bats from its recesses. In one day, he caught 52 specimens, probably all greater mouse-eared bats (Myotis myotis). A few minutes later, in the shadow of the campanile, still dressed in his vestments, he removed the eyes of the bats and released them. Four days later he returned. This time he caught 48 bats. He’d captured three of them before: they had no eyes. When he opened their stomachs, he found them filled with insects. Finally, there was no doubt. Even blind bats could navigate, hunt and survive as long as they had their hearing.
Fast-forward to 1938. Donald Griffin is a student at Harvard University. For his studies, he is placing numbered tags around the ankles of different species to aid the tracking of their seasonal migrations. Collaborating with Robert Galambos, who worked in the emerging field of auditory physiology, Griffin gained access to an early version of an ultrasonic detector. In a darkened laboratory, the pair ran a series of studies as elegant as Spallanzani’s – if less gruesome. Finally, with the modern apparatus, they were able to hear the staccato ultrasonic vocalisations that bats emit and bounce off their surroundings. And they showed that bats could use them to dodge obstacles – right down to thin wires – even in the dark. Griffin understood immediately that bats generate a 3D picture of their environment based on the way their vocalisations bounce back to them.
But it was Spallanzani, crouched in the darkness in 1793 with a string tied to a bat’s leg, who made the key breakthrough. It was Magnifico, high above Pavia in the darkness of a bell tower, who first discovered the truth about bats. Luckily for him, the poor flittermice never heard him coming.
This article appeared in print under the headline “The original batman”
