Not underground as in it burrows into the earth, but the formal noun referring to the London Underground. That’s right, as well as being an exceptional form of public transportation, the London Underground has it’s very own species of mosquito.
It was first reported during World War Two, when the tunnels of the Underground were used as overnight shelters, housing 180,000 people.
And then it was largely forgotten until a doctoral student, Katharine Byrne, started studying this subterranean pest. And found that the Underground mosquito is no longer able to interbreed with other mosquitoes:
“There are differences in both the mating behaviour and the reproductive biology,”
Read about it over at BBC, or read the original paper here!
Nothing in Biology Makes Sense! 
Fascinating!