MADRID city council has assured the public there is 'no existence of a swarm' of biting black flies in the metropolitan area, and that the cases reported to date are 'within the realms of normality'.
Concerns were raised recently after a residents in the Butarque area of Madrid had to be treated for a spate of bites, and the presence of Simulium trifasciatum, or 'black fly', was detected in the nearby Manzanares river.
Non-stagnant freshwater areas are the ideal habitat for these noxious creatures, since they lay their eggs in running water and the larvae attach themselves to rocks – and, ironically, cleaning up river pollution actually encourages them, because they need clean water to breed.
Environmental engineers from the city council have been closely monitoring the situation and have agreed to 'reinforce' control and prevention in the Manzanares river, but say the number of bites reported so far is 'normal'.
Insecticide specially designed to wipe out eggs, larvae and adult black flies is being used on the banks and in the wooded areas near the river, but the council stresses that these substances are not harmful to humans, animals or the environment.
Black flies do not carry infectious diseases and are not considered dangerous to humans or animals, except for small ones such as mice and birds when they strike in large swarms, although their bites normally require medical attention as their saliva causes an allergic reaction.
The flies remove pieces of skin and feed off human blood for some time, since their bite anaesthetises the area – as well as stopping the blood clotting so the insects literally have an on-tap supply.
They mainly go for ankles, backs of knees and ears where the skin is thinner, and wearing long sleeves or trousers is no barrier to them entering.
Wounds caused by black-fly bites are usually large, red and swollen.
Other than avoiding areas where they are known to be, the only effective prevention is to wear insect repellent containing DEET, the type usually recommended for anyone travelling in tropical rural areas.
Black flies in the river Ebro first found 12 years ago left 2,000 people needing treatment – enough to be considered an 'epidemic' – and by the following year, nearly 15 times as many people were affected.
But Madrid says the incidence this summer has been much lower and does not constitute an 'epidemic'.
Biting black flies are among Spain's most nuisance summer insects, along with tiger mosquitoes and the Asiatic wasp.
