Plantwatch: the cactus that lures bats with its fuzzy acoustic hat

Some flowers lure bats into pollinating them by stinking like fermenting fruit, cabbage, garlic and even urine. But one cactus flower tempts bats by turning into an acoustic beacon. Bats make high-pitched squeaks, too high for humans to hear, and use the echoes when the sounds bounce off objects for navigation and for finding objects in the dark. Many cacti in eastern Brazil bloom at night and are pollinated by bats, but some have no scent. Instead, one cactus – Coleocephalocereus goebelianus – grows what looks like a fuzzy hat near its flowers, a strange body called a cephalium. This helps focus the bats’ ultrasound towards the flower, and its dense structure may also help reduce background noise to make the bats’ echolocation clearer. The cactus also stands like a tall tower above the surrounding plants, making its acoustics even clearer. Some carnivorous pitcher plants also help bats to echolocate, using curved dish-like openings around their traps that reflect bat calls, helping them find the pitchers. The bats roost inside the pitchers and their dung fertilises the plant.