The 'black fly' (Simulium trifasciatum) is spreading across Spain, joining the Asiatic wasp and the tiger mosquito as one of the country's principal insect pests.
The black fly was first detected along the shores of the river Ebro in 2006, and shortly afterwards made its presence known in various different parts of Aragon, where some 2000 people had to receive emergency medical attention, constituting the first official plague of the insect in Spain.
The following year, 28,500 people in Aragon required medical attention because of black fly bites and now the people of Butarque (Madrid) have become the latest victims of a black fly plague, because of their proximity to the river Manzanares, which appears to be the ideal habitat for this aggressive insect.
Eggs are laid in running water and the larvae attach themselves to rocks. Breeding is highly sensitive to water pollution and according to Pedro Francisco Sánchez, head of Environmetal Health Services for the region of Murcia, "the cleaning up of Spanish rivers has paradoxically made them an even more ideal habitat for the larvae and we are now finding black fly in more and more places across the country."
A swarm of black flies are capable of capable of killing small animals like mice and birds, and although they do not spread any contagious diseases in Europe, the black fly bites, rather than stings, causing a much larger and deeper wound.
"When it bites, it removes a section of skin and injects both anaesthetic and a powerful anticoagulant from its saliva so it can feed for a while without us noticing it, but what affects us most is the fly's saliva, that can bring on an allergic reaction," explained Marta Naya, plague expert and spokesperson for the National Association of Environmental Health Companies (ANECPLA).
A biting black fly leaves a swollen wound several centimetres in diameter that can be aggravated by an allergy to the saliva, necessitating hospitalisation in some cases. In contrast to other flying insects, the black fly is active during the day and is capable of getting inside long-sleeved shirts and long trousers in order to reach human skin. Only the females of the species bite and they tend to zero in on areas of thinner skin, such as the nape of the neck or ears and ankles.
Health professionals recommend avoiding known black fly habitats, using repellents containing the active ingredient IR3535 (ethyl butylacetylaminopropionate), DEET (N,N-diethyl-meta-toluamide) or picaridin, and wearing heavy duty, light-coloured, long clothing to minimise the chances of being bitten.
