The Mosquitoes of the London Underground

Photo One by Walkabout12 - Own work, CC BY-SA 3.0, Walkabout12 - Own work, CC BY-SA 3.0,

The London Underground Mosquito (Culex pipiens f. molestus)(Photo One)

Dear Readers, I was much taken by an article in New Scientist about the evolution of urban species by Rob Dunn this week, and in particular his thoughts about the infamous London Underground mosquito. During the Second World War, unfortunate civilians who spent nights on the platforms of Underground stations to avoid the Blitz complained about being bitten unmercifully, but it’s only recently that genetic technology has advanced to a point where we can really work out what’s going on.

Photo Two by By US Govt - This media is available in the holdings of the National Archives and Records Administration, cataloged under the National Archives Identifier (NAID) 195768., Public Domain,

Sheltering in the Underground (Photo Two)

The original LU Mosquito came from the Fertile Crescent in the Middle East and lived above ground. These insects are active only during the warmer months, require a meal of blood before they can reproduce, and feed mainly on the blood of birds. However, as the mosquito spread north into colder climes, it survived by living in cities, particularly their underground regions such as sewers. The insect evolved new genetic characteristics, such as odour recognition, digestion and immunity, that would be useful in environments rich in organic waste.

However, it wasn’t just the genes that changed, behaviour did too. Both the underground and the above-ground mosquitoes are thought to be the same species, but the underground ones are active all year round, can reproduce without a blood meal, and prefer to feed on mammals: rats and mice in particular, but humans where they can find them. The underground mosquitoes are isolated from other mosquitoes, and their habitat can be compared to an island, as Dunn points out: the mosquitoes cannot disperse, and so they become more and more specialised. Cities such as Paris, Minsk, Tokyo and New York all have their own ‘Underground Mosquitoes’.

However, the isolation can have another, even more extreme, effect – it’s been shown that where LU Mosquito populations are isolated within the Underground network, they can start to become genetically distinct from one another. So, it was found that the mosquitoes found on the Victoria Line were different from those found on the Bakerloo Line. It’s quite possible that every underground line could have its own mosquito, though I suspect that lines with a larger proportion of stations which are above ground might be less distinct, because their mosquitoes can actually disperse and interbreed.

For us, though, as humans, it means that the old Petula Clark song ‘Don’t Sleep in the Subway’ has never been better advice.



6 thoughts on “The Mosquitoes of the London Underground

  1. Anne

    This is really fascinating. It is amazing how species continue to evolve to suit the environment they find themselves in – unlike humans, who bash things around to suit themselves!

    1. Bug Woman Post author

      I rather like the way that life will find a way, even in the most unpromising circumstances. It gives me a bleak kind of hope 🙂

  2. Julian Woodford

    Re: genetic isolation between the Victoria and Bakerloo line mosquitoes: perhaps they change at Oxford Circus!!!

  3. rescuedogdexter

    Interesting thank you. I am not surprised that there are mosquitoes on LU. After all the study a few years back showed how filthy it was down in the bowels of London. One of the London universities found (I think) 95 bacterias on the sears, handrails and seat undersides. Nine of those bacteria are resistant to antibiotics. Just a miasma of dust, disease and dangerous bugs down there. It wouldn’t shock me if they found a new alien species too.

  4. Claire

    Very interesting! Sounds like Science fiction: in a way ,it reminds me of John Wyndham’s «The day of the triffids ».


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