The London Underground Mosquito

27 November 2018

Interview with

Menno Schilthausen

If you wanted to go on a journey into the wonderful world of evolution, the London Underground might seem an unlikely place to start. But the tube tunnels have given rise to a surprising evolutionary connection that has nothing to do with trains: because the Underground has its own species of mosquito. Genetically distinct from its above-ground relative, the London Underground mosquito was first documented anecdotally during the Second World War. This story has inspired a new book called “Darwin Comes To Town – how the urban jungle drives evolution”. Francesca Fazey took a trip on London Transport to speak to the author, evolutionary biologist Menno Schilthausen...

Francesca - Nature gets into every gap. Even here, in the tube’s dark tunnels filled with smoke and grime and rushing commuters, evolution is at work. During the Second World War, London's residents used many of the tube line tunnels as makeshift air raid shelters hiding out with their families as the bombs rained down on their city. But many stories of the horror of this experience were punctuated with mention of an added menace: A particularly aggressive mosquito the likes of which the families had not been used to in their lives on the surface. Few people paid attention to these accounts but in the 1990s a research team found that there was truth to the stories of a sinister underground mosquito.

Menno - The scientific name is Culex molestus, or sometimes people say Culex pipiens molestus, so so they say it's a subspecies of the regular mosquito, Culex pipiens, but it is actually quite different so I prefer to call it a separate species.

Francesca - Menno Schilthausen is an evolutionary biologist at the National Natural History Museum in the Netherlands.

Menno -  It is different from its closest relative, you could say the aboveground mosquito, in three ways. The underground mosquito prefers to bite humans instead of birds, which the aboveground mosquito does. The underground mosquito does not mate in these large mating swarms that you see above ground, the underground mosquito really mates one on one in very confined spaces, and also the underground mosquito does not need a blood meal before it can lay eggs, which the aboveground mosquito does need. So you have three fundamentally different aspects of this of its life history that have evolved away from the ancestor which was the aboveground mosquito.

Francesca -  In the short time in which humans had developed tunnels and begun inhabiting underground spaces a whole new species had evolved.

Menno - One of the cool things I think is that in the London Underground these mosquitoes have not only evolved away from their ancestors aboveground but also mosquitoes in different underground lines are genetically different from each other because they are sort of separated and live in different worlds. And so those mosquitoes in the Circle Line are genetically a little bit different from the ones in the Piccadilly Line for example.

Francesca - Like most biologists he grew up loving the great outdoors as far away from the effects of people as he could get. But unlike many others his passion for evolution and studying natural selection has steered him back towards the cranes and cars of the concrete jungle. So much so in fact that he has written a book in which he outlines the amazing ways that nature adapts right in front of us in urban environments.

Menno - In cities, evolution goes really really fast so you can actually watch evolution take place over a time span of decades, sometimes even years, and that makes evolution really tangible and I think that's a really good way to show that evolution is a very mundane process really, you don't need to study fossils you don't need to go to the Galapagos to see it happening, it's happening everywhere all the time including in your own street and in your own backyard.

Francesca - Menno’s favorite example of urban evolution, he tells me, is the city blackbird which was the first bird to colonise cities in Europe and now shows multiple changes from its forest ancestor.

Menno - The city blackbirds have shorter beaks, in some cities they also have shorter intestines. They don't migrate anymore, the forest blackbirds, which still exist of course, they do migrate away during the winter, the urban blackbirds don't.

Francesca -  But when is adaptation evolution and when is it just learning. Take the famous example of bluetits in the UK who learned to peck open the milk bottles left outside people's front doors. That was learned behavior. When would it represent an evolutionary shift. Well it depends on whether genetics are involved.

Menno -  Of course there's not a gene for opening the caps of milk bottles but there are genes for inventiveness for something called neophillia. So so being curious about new things and also for tolerance towards humans. Those are all things which have a genetic basis.

Francesca -  Since 2007 more than half of the world's human population have lived in urban environments. And by 2030 it's believed that a full 10 per cent of land on Earth will be covered by a city of some sort.

Menno -  Whether we like it or not the world at the moment is in a situation that is unprecedented. We've never before had a situation where a single species - namely humans - is affecting the ecosystems of the world everywhere, and in such a drastic way. Again whether we like it or not we are witnessing a very important, unprecedented crucial change in the history of life on Earth and we should be studying that. Right now humans are one of the most important evolutionary forces and we should really take that into account.

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