Black flies thrive in Spain's heat: How to avoid their bites

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Black flies thrive in Spain's heat: How to avoid their bites
Year after year, ANECPLA has increased the alert level for the prevalence of la mosca negra (black fly) in urban areas across Spain. Photo: Fritz Geller-Grimm/Wikipedia

Several Spanish regions are dealing with a sharp rise in black fly populations, with experts warning of the potential risks black their blood-sucking bites pose to our. Here are their recommendations to keep them away.


What's the latest?

In recent years, health experts in Spain have been warning residents and visitors about the proliferation of black flies in several regions across the country. 

In August 2023, the regions of Murcia, Madrid, Valencia, Catalonia, Aragón and Andalusia are seeing what's been referred to in the press as a plaga (infestation) of the mosca negra

Spain’s National Association of Environmental Health Companies (ANECPLA) is again informing people that the black fly poses a "potential risk to public health" which can lead to hospitalisations in some cases. 

"The black fly bite is in the shape of a saw, their saliva can cause very alarming allergic reactions or infections, which in some cases require hospitalisation," ANECPLA warns. 

People bitten by black flies often develop an itchy and painful welt or rash several centimetres wide that sometimes even bleeds, as well as swelling in the affected area that can last up to a month.

ANECPLA has said "high temperatures are one of the main factors leading to a peak in the volume of the black fly population," and by giving some forewarning "larvicide treatments can be executed to combat the plague in its early stages of development".

Their president Sergio Monge adds that "climate change and globalisation" are also having an impact on their proliferation.


"Their lifespan, which can last from a few days to several months, can be reduced by half when it is very hot, thus producing a demographic 'boom' and consequently an increase in bites." 

Just like with other insect species, scientific studies show that climate change encourages their reproductive cycle, particularly in areas close to rivers where they tend to live. 

Increased conservation and maintenance of rivers in urban areas has also helped them thrive, as black flies proliferate in clean and circulating bodies of water.


Globalisation is playing a role in the rise of black flies in Spain as well. ANECPLA has warned that the black fly is a transmitter of serious infectious diseases such as onchocerciasis (river blindness), endemic to several countries in sub-Saharan Africa, Brazil and Venezuela, where according to the World Health Organisation (WHO) 18 million people are currently infected with river blindness and almost 270,000 have gone blind as a result.


A drop in bat populations has also meant they have no natural predators to keep numbers down. For over a decade, authorities in Zaragoza have been trying to increase the bat population around the Ribera de Ebro protected area to address the problem.

Residents of the district of Villaverde outside of the Spanish capital have been plagued by black flies for years, attracted by the abundance of vegetation, the nearby Manzanares river and the swimming pools.

"We have to go outside in long sleeves because they bite you, even if you use mosquito repellent," one resident told local TV channel Telemadrid, insisting that it’s preventing outdoor activities from taking place in Villaverde.

Year after year, ANECPLA has increased the alert level for the prevalence of la mosca negra (black fly) in urban areas across Spain.



What to do if you get bitten by a black fly and how do you avoid it?

Black flies - also referred to as buffalo gnat, turkey gnat, or white socks - don’t sting, they bite. 

This 6mm insect is in fact looking to suck blood just like a mosquito, but as the amount they ingest is usually greater, the pain is more intense and long lasting. 

You may not feel the bite initially as the black fly injects an anaesthetic that is both a vasodilator and an anticoagulant, allowing them to go unnoticed while feeding.

The bites are not venomous but they can cause swelling or bleeding and in some cases an allergic reaction, in which case it’s advisable to go to the emergency room.

Other symptoms can include headache, nausea, fever, and swollen lymph nodes.

If you do get bitten, try to avoid scratching the wound, wash it and disinfect it. You can apply ice or a recommended cream. 

Pay special attention if you’re in a part of Spain that’s close to a river, although black flies are found all across the Spanish territory. 

Unlike other flying insects, the black fly acts during the day (particularly active in the early morning and in the evening) and is able to get under clothing and reach the skin to achieve its goal.


Some of the tips released from ANECPLA to avoid being bitten by this insect are as follows:

  • Dress in light clothing and avoid bright colours that can attract swarms.
  • Avoid walking along the riverside or in closeby areas, especially in the late afternoon.
  • Install mosquito nets on doors and windows in risk areas.
  • Avoid the accumulation of water outside of your home.
  • Keep swimming pools, water tanks and other water deposits covered when not in use.
  • Check your home’s drains and sewage system.
  • Use certified repellants (especially those containing citronella).
  • Contact professionals if you’ve been unable to solve the issue.


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