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I first saw the bats, as it happens, a few Halloweens ago. I had stopped by the main Berkeley library on the way from work, before heading home to hand out candy to the little extortionists, and it was dusk as I was leaving the building. Something caught my eye: what appeared to be birds—starlings? blackbirds?—flying away from the business school across the street. Birds with an odd flickering flight. 

No, not birds: bats. And they were emerging from the Spanish tiles of the building’s roof. 

We’re not talking hordes of bats, a few dozen at most. It wasn’t Carlsbad Caverns. It wasn’t even the Congress Street Bridge in Austin, Texas, where folks gather on summer evenings to watch bats fly out on their nightly hunt. But it was a stirring sight in its own way. 

Somewhat later I met bat rehabilitator Pat Winters (and some of her charges, which were really engaging creatures) at an Audubon Society presentation, and asked her about the downtown bat flight. She knew them, of course. They were Mexican free-tailed bats, a species that finds Spanish-tile roofs congenial roosting places. She also knew of another roost on the UC campus. 

Mexican free-tails, also known as Brazilian free-tails or guano bats, may be the most abundant bats in North America. “Free-tailed” refers to an anatomical peculiarity. Most bats have a skin membrane, the uropatagium, which stretches between their hind legs from ankle to ankle and completely encloses their tails. Free-tails have a reduced uropatagium that leaves the tip of the tail, well, free. Since bats use the membrane as a scoop to catch insects in flight, this would seem to put free-tails at a competitive disadvantage. But you wouldn’t know it from their numbers. 

California lacks the enormous aggregations of bats that occur in the Southwest. In summer, female free-tailed bats gather in nursery caves to give birth and rear their single pups. Bracken Cave in Central Texas harbors an estimated 20 million bats, the largest colony of any mammalian species. Other caves in the region have bats in the lower millions. Within the cave, bat pups group together in creches at densities up to 500 per square foot. Somehow returning females are able to locate their own youngsters by voice and smell, although some freeloading inevitably occurs. 

On the West Coast, free-tails use buildings in lieu of caves. They also differ from their Texan kin in being non-migratory. Free-tails are found year-round in California and Oregon, going torpid when the weather turns cold and bugs are scarce. 

A free-tailed bat nursery cave is no place for the faint of heart or weak of stomach. Here’s how Roger Barbour and Wayne Davis described the setting in Bats of America: “The bats are always alert, and the disturbance of the intruder’s lights causes them to peel off from the great clusters….The floor and the walls of the cave soon seem to be crawling with them, and they collide with the observer in ever increasing numbers. They cling to him and crawl upward to reach a high point from which to launch into flight…one gets the feeling that he may be smothered by the animals as he sinks deeper into the loose and sometimes soggy guano which covers the cave floor.” All this plus stifling heat, powerful ammonia fumes, and biting insects.  

You have to appreciate, then, the dedication of the bat wranglers who took part in one of the loonier episodes of World War II: Project X-Ray.  

It all started when Dr. Lytle Adams, an oral surgeon from Irwin, Pennsylvania, had a sort of epiphany while driving back from Carlsbad after Pearl Harbor. Adams was musing about what bats could possibly be good for when it struck him that their tendency to fly into buildings could be exploited for strategic purposes. As he put it in a letter to FDR: “This lowly creature, the bat, is capable of carryng in flight a sufficient quantity of material to ignite a fire.” 

Bats could be refrigerated to induce hibernation, rigged with little incendiary devices and parachutes, and airdropped over Japanese cities. “The effect of the destruction from such a mysterious source,” Adams wrote, “would be a shock to the morale of the Japanese people as no amount of bombing could accomplish.” 

People in Washington took this seriously. As Jack Couffer recounted in his 1992 memoir, The Bat Bomb, X-Ray was funded to the tune of a couple million dollars. A Harvard chiropterist was assigned to the project, and its staff came to include actor Tim Holt (Treasure of the Sierra Madre), an alumnus of the Capone organization, and, as mascot, a young Bengal tiger. 

Bats were gathered from some of those Texas caves, and by the spring of 1943 the crew was ready for field tests, first over a dry lake in the Mojave, then at an Army airfield near Carlsbad Caverns. However, technical difficulties were encountered. Texas free-tailed bats, being migratory, did not take naturally to hibernation. When released from planes, some of the bats did not so much fly as plummet. During the Carlsbad test in June, napalm-bearing bats got away from their handlers and flew to the airfield’s control tower, then to nearby barracks. The base erupted in flames, as did a general’s automobile. 

The bat-bomb project survived this debacle, but not for long; the Chief of Naval Operations (the Army Air Force had lost interest, but the Navy had signed on) pulled the plug the following February. By then, plans for another kind of weapon were far advanced at Los Alamos.  

The next time you pass the library in an autumn twilight, though, think of this footnote to history, and look up.›