the black fly (Simulium erythrocephalum) is not an invasive species in Spain. it is an autochthonous insect of iberian ecosystems, yet its numbers have surged to levels not seen in recent years. in madrid, catalonia, valencia, murcia, aragon and andalusia, residents and health professionals alike perceive these flies as a troubling plague, impacting both people and animals.
in madrid alone, health services treated more than 300,000 people for bites from 2015 to 2019. health authorities report that more than 20,000 patients are affected annually in zaragoza, a figure that was under 4,500 a decade ago according to earlier data.
the bite of the black fly is notably intense. this insect tends to bite the skin rather than merely stinging, leaving visible bruising that can last several days to a week. many residents in affected towns have sought emergency care for large swellings, dermatitis and severe itching.
the impact is not limited to people. pets and farm animals are also affected, with heat seemingly favoring species such as sheep, cattle, horses and goats.
these insects gather in large clouds around animals, harassing and biting persistently. as a result, many farmers adjust grazing times to minimize exposure, and veterinarians report busier summers as these pests return.
the black fly is very small, typically 3 to 6 mm, more akin to a wasp in appearance than a mosquito.
experts point to factors such as riverbed pollution and inadequate cleaning of waterways as contributors. some analyses link outbreaks to delays in river channel maintenance during recent years, which allowed larvae to thrive on vegetation in contact with fresh water.
warmer temperatures also accelerate hatching, while the gradual decline of natural predators like swallows, swifts and bats reduces biological control. the protection of these predators is part of broader strategies to keep nuisance populations in check.
the bite is often subtle. it does not cling heavily to the skin, making it easy to miss at first. it releases a local anesthetic and an anticoagulant, allowing blood to flow more freely. many people do not notice the sting until later, when irritation grows.
the bite typically inflames the skin with a central red spot. in such cases, applying cold and seeking medical care for signs of allergy is advised. medical authorities note that while the bite is painful, it does not transmit disease in the same way as some other insects.
outdoor activity in certain areas can be uncomfortable as temperatures rise and black flies populate urban districts. authorities have conducted fumigation campaigns in affected regions in the past, and ongoing management remains a priority where infestations reappear.
regional efforts to combat black flies have included coordinated treatments along major river corridors. funding structures involve multiple levels of government, with a mix of regional and local support to sustain control programs.
prevention tips include wearing long, light clothing; avoiding prolonged time near rivers or reservoirs; installing window nets at home; eliminating standing water around properties; and using approved flying insect repellents.
questions commonly asked include how to prevent stings, what symptoms to watch for, what treatment steps to take, and when to seek a health center or specialist for guidance. practical recommendations emphasize early care for skin cleaning, cooling the bite area, avoiding scratching, and using soothing products as directed.
for authoritative guidance on black fly bites, consulting a medical professional is advised. health authorities encourage people to seek timely care if there is difficulty breathing, swelling of the face or throat, or signs of a severe allergic reaction.
in madrid, the summer experience can be marked by the high heat and a noticeable presence of black flies, but the focus remains on practical prevention, prompt treatment and coordinated regional action to reduce nuisance and protect public health.