For the last six years, Paul Racey has been trying to find a female eastern sucker-footed bat. He has failed. The bats only live in Madagascar and since 2007, Racey’s team have tramped through the country’s eastern forests with nets, bags, and devices that detect the bats’ sonar. They’ve captured 298 individuals, some many times over. But every single one of them was male.

Where are the females? Why are they so ridiculously hard to find? And why do they segregate themselves from the males? No one knows. After so much fruitless searching, Racey doesn’t even have a good hypothesis.

All he knows is that the females must exist. For a start, a Smithsonian team once collected a female sucker-footed bat