Home Sciences The plague of the black fly and its powerful bite spreads throughout...

The plague of the black fly and its powerful bite spreads throughout Spain


The black fly (Simulium erytrocephalum) is not an invasive species in Spain, but rather it is an autochthonous insect of the Iberian ecosystems, but which for a few years has been experiencing unprecedented peaks in its populations. At least, that is the general perception that they have in Madrid, Catalonia, Valencia, Murcia, Aragon and areas of Andalusia, where these flies are becoming a true plague that attacks both people and animals.

From 2015 to 2019, in Madrid alone, the medical services had treated more than 300,000 people suffering from its bite. In Zaragoza there are more than 20,000 affected each year, when a decade ago they did not exceed 4,500, according to health sources.

And it is that the bite of the black fly is especially intense. More than stinging, what this insect does is bite the skin, leaving a visible bruise that can last for several days and up to a week. Many residents of the affected towns have had to go to the emergency room suffering from large swellings, dermatitis and severe itching.

But not only people. Pets and livestock are also affected by the black fly, a species that seems to be favored by heat.

It especially attacks sheep, cattle, horses and goats, but also dogs and other pets. These insects form a large cloud that surrounds the animal and do not stop harassing and biting it, which is why many farmers have been forced to vary the times in which they take the animals out to avoid this plague as much as possible. Nobody seems to be safe. Veterinarians have also had extra work for a few summers.

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This annoying insect is very small, it measures between 3 and 6 mm, it is more similar to a wasp.

Apparently, its proliferation is due to the inadequate cleaning of riverbedsproduct of the months of confinement due to the coronavirus pandemic, according to numerous media outlets in the affected areas.

This black fly lays its larvae on vegetation that is in contact with fresh water. Since the cleaning of these channels cannot be carried out correctly, these insects have multiplied.

In addition, the high temperatures have also favored an early hatching, as well as the gradual disappearance of its predators: swallows, swifts and batsinsectivorous species whose protection is necessary precisely to keep this type of annoying species at bay.

Its bite is more stealthy than that of a mosquito. Supports its legs as little as possible on the skin, so it goes unnoticed. It injects an anesthetic more powerful than that of mosquitoes and an anticoagulant to make the blood more fluid. We do not realize that it has stung us until a good time later.

The bite is highly inflamed with a red dot in the center. In these cases, it is best to apply ice and go to the emergency room if there are symptoms of an allergic reaction (see recommendations, below).

The bite will cause an inflammation that, despite being painful, does not present any risk of disease transmission, according to the Spanish Society of Emergency Medicine (SEMES).

In Madrid, with the arrival of high temperatures, a walk in the open air in certain areas can become torture, due to the large number of black fly specimens that tend to populate the outskirts of the capital.

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For this reason, already in 2020 the City Council carried out an important fumigation of the Manzanares River to eradicate this insect, but the problem seems to have reproduced this year.

The same happens in Catalonia. In February last year, the Ebro Environmental Policy Consortium (Copate) carried out the first treatment against the black fly plague in the final stretch of the Ebro riverafter last year this action demonstrated its effectiveness.

This body had a budget of 1.3 million euros to combat the black fly and the mosquito. Half was provided by the Generalitat and the rest by the Provincial Council of Tarragona and the municipalities of the Delta de l’Ebre.

1º How to prevent the sting?

-Dress in long, light clothing

-Do not spend much time in rivers or reservoirs

-Install mosquito nets in your home

-Prevents accumulations of water

-Use flying insect repellents

2nd What are the symptoms?

-High pain in the affected area

-Central red and bleeding spot

-Inflammation of the affected area


-Wheal or spot around the affected area

3º What is the treatment?

-Clean and disinfect the affected area with an antiseptic

-Apply cold

-Don’t even think about scratching, you’ll only make it worse

– Product soothes bites

4th Consult a health center or your specialist

SEMES website on the black fly: https://www.semes.org/semes-divulgacion/picadura-de-mosca-negra/


Environment section contact: crisisclimatica@prensaiberica.es

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