Are there really mosquitoes on the tube? Is it true that they've evolved into different species, each frequenting a different tube line? How did they ever get there?
We've always wondered about the mozzie rumours. Now we have some answers for you, thanks to naturalist Bob Gilbert. Bob was the author of Ghost Trees, an absolute bobby-dazzler of a book about the wildlife in the author's local area of Poplar. His new book, The Missing Musk: A Casebook of Mysteries from the Natural World, casts the net much wider and, among the titular mysteries, it catches some of London's mosquitoes. Bob devotes many pages to the maligned insects in the book, as well as wider histories of mosquitoes in Britain.
We asked if he'd be kind enough to answer a few questions for us. He bit.
Has London always had mosquito populations, or are they a more recent arrival like parakeets?
There have always been mosquitoes in London. In fact they were once far more numerous than they are today. Mosquitoes were a constant presence in the lowlands and marshes of the English east coast and these extended all the way up the Thames estuary and into the environs of the city. It has largely been forgotten that malaria, spread by mosquitoes, was endemic in these areas until the early 20th century. The marshes of Lambeth and Westminster were particularly notorious and between 1850 and 1860 it was estimated that one in twenty patients at St Thomas’s hospital were suffering from the ‘ague’, with the figure, in some years, much higher.
Do we know how many different mosquito species live in London and the south-east? Do they all bite?
All mosquito species bite, but they don’t necessarily bite humans. Many of them feed on birds or other mammals, and it has to be remembered, too, that only the females bite. They need the blood feed to facilitate egg laying; the more innocuous males feed on nectar or the juices of rotting fruits. Of the estimated 34 species of mosquito found in Britain, several occur in London, some of which will also enter our homes. Among them is Theobaldia annulata which is distinguished by the bold black and white stripes on its legs. I recently found it in my bathroom. It comes into our homes to hibernate and is the most common source of winter bites.
How did mosquitoes come to be associated with the Underground?
Mosquitoes first seem to have entered the London Underground during the second world war. At the height of the London blitz, and despite initial Government opposition, up to 150,000 people were sheltering in the underground every night; sleeping body-to-body on the platforms and even, when the trains stopped for the night, on the escalators or in hammocks slung across the tracks. It became like a small town down there with medical services, canteens, entertainment, even a library in some.
Nonetheless conditions were grim. People were packed together, sleeping on uncomfortable surfaces, spreading coughs and colds, hardly even able to turn in their sleep and fearful of what was going on above. The smell was also highly unpleasant — except to the mosquitoes, of course, who would have been drawn by this as well as by the body warmth and other chemical signals given off by the huddled masses. Others would have been accidentally transported into the network amongst the paraphernalia that people brought down with them each night. They were eventually to become such a problem that special squads were set up to try and deal with them — which they did with almost military discipline.
There’s an old factoid that says every tube line has its own species of mosquito. It sounds deeply implausible to us, but is there any truth in this?
The idea that every tube line is evolving its own species — a Victoria line mosquito, a Central line mosquito and so on — is a popular one and even appears in some scientific papers. It is, I believe, based on an error.
Researchers in 1999 identified the species of mosquito now living in the tube network as Culex pipiens. What puzzled many people was that this species was not thought to bite humans at all but to feed from birds. The fact that, in the tunnels, it had now switched to human blood, together with its other adaptations to life underground, suggested that evolution was happening at a remarkably rapid rate, and one that challenged orthodox Darwinian theory. Moreover this ‘speciation’ was so fast it might even imply that populations of mosquitoes living on different tube lines, and separated from each other by the action of trains, might themselves evolve into separate species. My research, however, showed something different.
Though seemingly forgotten, several pre-war records already existed of above-ground Culex pipiens that had switched to drinking human blood. Moreover, most of these reports came from urban areas, and, in London, from a particular area around Trafalgar Square. I have no problem with challenges to neo-Darwinian theory but in this instance I believe the evolution of this different strain of C. pipiens had already happened amongst surface dwelling mosquitoes. When, alongside various others, they found their way into the war-time tunnels, it was this strain that was already best adapted to survive.
Have to admit, we've used the tube more intensively than most people over the years, and we've never seen a single mosquito, let alone been bitten by one. Are we just lucky, or are they now confined to tunnels and parts of the network where the public don't go?
Despite being a Londoner, and always being on the look-out for them, I, too, have never encountered the underground mosquito. They continued to be well attested in post-war years, however, both by workers on the underground and researchers who walked the tunnels at night — something I was unable to get permission to do. I do wonder, however, whether their populations survived the Covid lockdown when usage of the system dropped dramatically and the human prey would have been less available. Something similar certainly seems to have happened to the underground mice: pre-Covid they were a common sight at many stations. In the last 18 months I have seen only one mouse at one site.
Given the warming climate, are we likely to see more mosquitoes in London? Could malaria become a problem again?
The more significant aspect of climate change in this context is its impact on the malarial virus Plasmodium vivax. Currently it is only viable here in the summer months. A warming climate gives it a longer time to develop, and across more of the country. A greater concern, however, surrounds the arrival of new, invasive species of mosquito and the diseases that might accompany them. Among these is Aedes albopictus, commonly known as the Asian tiger. A carrier of dengue, chickungunya and zika virus, it has been breeding in Kent since 2016 and reached London in 2019. According to the National Contingency Plan for Invasive Mosquitoes, ‘the problem of emerging or re-emerging vector-born diseases may intensify soon.’
The Missing Musk: A Casebook of Mysteries from the Natural World by Bob Gilbert is out now from Hodder and Stoughton. Its natural mysteries include the mysterious hardiness of tardrigrades, and why all the world's musk plants stopped smelling in 1913.