John Lloyd - Most Interesting: The Best of the QI App as Chosen by Users

Surely a life doesnt get any bleaker than that of the deep-sea anglerfish? Two miles down in the endless darkness, a gloomy motionless lump of brittle bone, atrophied muscle and paper-thin black skin with only luminous bacteria for company. A life spent doing nothing except waiting, often for months at a time, turning your light on and off in the hope that it will attract some other creature out of the inky gloom long enough for them to stray too close to your cavernous mouth...

The male Photo-corynus spiniceps is the smallest known vertebrate, a quarter of an inch long, about half a million times smaller than the female.

The name anglerfish is used for about 300 species including sea toads, frogfish, batfish and monkfish which attract their prey with a long, flexible appendage like a fishing rod, typically growing out of the middle of their heads. At the end of it, in place of a dangling maggot, there is the esca (Latin for food), which can be wiggled to mimic live bait. In the deep-sea anglers, the esca lights up, thanks to a chemical process controlled by the bacteria that live on it. In return for light, the anglerfish supplies them with food. Different anglerfish have differently shaped escas. It was once thought this was to attract different prey, but its now believed that they all have a similar diet. Perhaps having a big, bendy, glowing rod sticking out of your head is a form of sexual display.

The deep-sea anglers are some of the most ugly and outlandish creatures on the planet. They have an elastic stomach that can swallow prey twice as large as themselves (it even has a light-proof lining in case they swallow luminous fish). To prevent their prey escaping they have backwards-facing teeth in their mouths and another set of teeth in their throats. The female Illuminated netdevil ( Linophryne arborifer ) looks like a fluorescent root vegetable, with a black bulbous body and two shimmering lures streaming off like psychedelic foliage. Her Latin name means tree-shaped toad that fishes with a net. The Hairy seadevils ( Caulophryne polynema ) huge spiny fins have a decayed look, its body is covered in unpleasant pale hairs and its lure looks like a frayed stick of liquorice. It has one of the most sensitive lateral lines of any fish the tiniest movement triggers the opening and closing of its jaws. Elsmans whipnose ( Gigantactis elsmani ) swims along upside down, trailing its lure along the seabed. The Wolftrap seadevil ( Lasiognathus saccostoma , or hairy-jawed sack-mouth) has a lure with three shining hooks on the end that it casts forwards like a fly-fisherman. Prince Axels wonderfish ( Thaumatichthys axeli ) has its lures hanging down from the roof of its mouth like a pair of fluorescent tonsils.

The male deep-sea anglerfish is much smaller than the female and doesnt have a lure. Hes interested in mating, not fishing. He uses his giant eyes to look for a suitable female, and his enormous nostrils to sniff out her pheromones. Having found her, he latches on to her with his teeth and then starts to disappear. Scales, bones, blood vessels all merge into those of the female. After a few weeks all thats left of the male are the testes hanging off the females side, supplying her with sperm. Females have been found with eight testes attached to their sides.

In some species, if the male fails to find a female, then he will eventually turn into one himself and grow massively in size. As the anglerfish themselves are wont to remark: theres only one thing worse than being an anglerfish and thats being a male anglerfish.

Beaver

Beavers have a greater impact on their surroundings than any creature other than humans. They build instinctively: put a young beaver in a cage and even without trees or running water, it still mimes the process of building a dam. They can chop down a tree with a 6-inch diameter in less than an hour. Some scientists now think the disappearance of the Pennine forests and the creation of the Fens were due to the beavers that lived in Britain until the early thirteenth century (the town of Beverly in Yorkshire is named after them).

Beavers are rodents, like large squirrels. There are only two species: the Eurasian ( Castor fiber ) and the North American ( Castorcanadensis ). Although similar in size and appearance the two have been separated for 24,000 years, so can no longer interbreed. They are larger than you might think. A fully grown beaver is the size of an eight-year-old human. The Giant beaver ( Castorohioensis ), which became extinct 10,000 years ago, was the size of Mike Tyson.