Mosquitoes in multitudes

  • Culex pipiens, the most common mosquito in Britain

    Culex larvae

    Cliffe Pools on the Hoo Peninsula, Kent

    The Hoo Peninsula (Google Maps).

  • Mosquitoes in multitudes
    09.08.2012 15:32


    The infrequent days this summer when we have been able to loaf in our gardens and enjoy the weather we have been blighted by mosquitoes.

    Although there is little evidence yet for a year-on-year increase in mosquito numbers, the weather conditions during the summer have been ideal for a boom in the population this year.

    Mosquitoes breed in slow-moving or stagnant water, and the persistent and often heavy rain that has typified much of this summer caused flooding that has left plentiful pools and brimming water butts in addition to permanent groundwater. Subsequent warmth has been a boon for these fecund creatures.

    About thirty species of mosquito reside in or visit the British Isles but only a few of these are interested in the taste of human blood, and of these it’s only the females. Others dine on cattle, or on wild mammals such as rabbits, or on amphibians. The contest between a mosquito and a frog’s tongue might be an interesting one.

    Bird blood is the tipple of choice of Britain’s most common species, the small brown “house mosquito” Culex pipiens. However, there is a variety called Culex pipiens f. molestus that does trouble the human population in a few locales – most notably in the warmth of subway systems. It earned the name “London Underground mosquito” after incessantly preying on Londoners sheltering in Underground stations from the Blitz.

    However, the insect you are swatting will most likely be the woodland mosquito, Ochlerotatus cantans, or the relatively large Culiseta annulata, known as thebanded mosquito, which, with its penchant for water barrels and dirty water, often plagues towns and cities. The salt marsh mosquito, Ochlerotatus detritus, also bites, but none of these species transmits disease.

    Another mosquito, Anopheles, might pose more of a threat, though. Both Anopheles plumbeus and Anopheles atroparvus are capable of carrying malaria, and both are found in the southeast of England, with A. atroparvus relishing the North Kent marshes.

    Malaria was well known by Chaucer and Shakespeare and was called “ague” or, because of its prevalence in estuaries and swampy areas, “marsh fever”. It seems to have been endemic throughout the estuaries of southeast England, the Fens and the marshes of northern England’s coasts in the Middle Ages but vastly improved healthcare in recent decades has almost eradicated it.

    However, there was an outbreak following the First World War, when soldiers returning from northern Greece with malarial symptoms were billeted on the Hoo Peninsula near Rochester, Kent, to recuperate.

    This marshy spot between the Thames and Medway estuaries could not have been a worse location.

    Mosquito larvae do not spring from the egg ready laden with the parasites that spread malaria. Instead the adult fly contracts the disease from people or its other prey and can then infect the next living creature it feeds upon.

    When the peninsula’s resident Anopheles atroparvus mosquitoes attacked the war veterans they picked up malaria and spread a minor epidemic across Kent. Although no fatalities were recorded, at least 500 people contracted the disease.

    There is less chance these days of such an outbreak; but we need to be wary of the possibility, however, remote at the moment, of greater threats. One such may be the Asian tiger mosquito, which carries Dengue fever, yellow fever and encephalitis, spreads to new niches rapidly, and has become well established in Italy with potential sightings as far north as Belgium.

    If Britain’s summers continue to be wet but still occasionally hot then who knows what tiny flying beasts may arrive.

    By: Stephen Davenport