You see, there is an insect called the lantern bug, and its idea of a great night out is sit on the bark of a tree, sucking up the sap. It does like a spot of sap, but it finds it a bit too sugary, so after a while it starts to poo out the excess blobs of sugary stuff. And because evolution is bat-shit loopy, it has evolved to have a flicky spatula on its bum (!?) so it can flick the sugary poo a long way away. Apparently it does this to avoid attracting ants. (Some species invent Tupperware, others evolve spatulas on their bums. Go figure.) Anyway, moths like sugary things, and therefore moths have evolved to come along, position themselves right behind the lantern bug's bum... and catch the sugary poo and suck it all up, yum yum yum. Or alternatively, YEUCH, if you're not a pervy scatologically obsessed moth.
For the disbelieving or curious, footage of both this peculiar scene AND the shagging slugs from last week can be found on the BBC website. And to think they call themselves a family channel.
Coming next week: spiders in bondage (probably).