The black fly

What is a black fly?

The black mosquito is a blue-gray to black mosquito up to six millimeters in size, whose females suck blood in warm-blooded animals and humans. In doing so, they do not stab the host in the narrower sense, but create a wound with their mouthparts, from which they then suck. The black fly feeds on the nectar of many plants, only the females need blood for egg development. They track down their possible host through the smell of carbon dioxide and optically.

Which diseases are transmitted by the black fly?

The black fly's bite is very painful and often leads to local bruising and severe swelling. The secretion of the hormone histamine often gives rise to pseudo-allergic reactions that can be dangerous.

Many black flies transfer poisonous substances into the wounds of people who have been stung, causing them to become infected with pus. This first local infection often leads to inflammation of the lymphatic vessels, which can lead to blood poisoning.

African subgroups of the black flies in particular transmit roundworms, which is called "onchocerciasis". Most infected people complain of lumps and inflammation of the skin. About ten percent of the sick go blind due to the colonization of the worm, which in this context is referred to as "river blindness".

In Europe, too, the black flies transmit dangerous diseases such as Lyme disease, which can lead to pain, inflammation and nerve failure.

What does the black fly look like?

Since black flies are rather small mosquitos and fly silently close to people, their bite is usually not noticed. In doing so, they do not stab people directly to suck blood, but rather bite a wound first. Blood collects in it, which is constantly flowing in thanks to an anticoagulant in the blackfly's saliva. The mosquitoes then drink the blood from these “pools”. The bitten person then often notices a small area of ​​bleeding and / or a bloodshot point on the skin.

In addition, the hormone histamine in the blackfly's saliva can cause a small nodule under the skin. In the process, a small purulent blister often forms on the site of the bite and a reddening of one to two centimeters around the bite site. The itching and swelling of the mosquito bite is caused by the hormone histamine in the mosquito saliva, which is then released further by your own body. It actually represents a defense reaction of the body. However, excessive scratching can carry infectious agents into the wound, which can then lead to severe inflammation.

Concomitant symptoms

In addition to the first pain of the black fly bite, swelling and reddening of the bite may occur over time. Most of the time, those affected complain of itching, which they give in by scratching.

In some, fortunately rare cases, stronger, allergic symptoms can also occur. Hives on the skin near the bite site and in more distant locations, a severe rash and even shortness of breath are caused by histamine, which is present in small amounts in the blackfly's saliva. Other toxic substances in this saliva can also set in motion a cascade in which other hormones and immune cells cause these stronger symptoms, including allergic shock.


The blackfly stinging and sucking blood can cause swelling around the bite. This is caused by local inflammation triggered by toxic substances and the hormone histamine.

The mosquito itself ensures that these substances get into the bite wound by secreting saliva mixed with them. The affected areas of the skin set in motion a cascade in which there is an increased influx of blood and fluid into the tissue. The swelling caused by this contains not only fluid but also immune cells that put an end to the inflammation.

Cooling and anti-inflammatory pain relievers such as ibuprofen, diclofenac, and the like can help fight the swelling faster.


The poisonous substances and the histamine in the blackfly's saliva can resolve an allergy. This can manifest itself through increased irritation with itching and reddening as well as large swelling.
In other cases, general malaise and even shortness of breath may occur. Some patients report headache, palpitations and even fever in this context. In the worst case, allergic shock with cardiovascular failure can occur. Fortunately, these appearances are very rare.

Read on below: Allergic reaction to a mosquito bite

Possible complications


A bruise around the black fly's bite can be caused by anticoagulant substances in the mosquito saliva. Small bruises from scratching and pressing the wound are also common. These usually recede very quickly and heal without consequences.


Inflammation of the bite site can be triggered in two ways: On the one hand, bacteria are released into the wound by some black flies with the suction process, on the other hand they can get into the wound when scratching, since bacteria occur naturally on the skin of every person.

Blood poisoning

With blood poisoning as a result of a mosquito bite, patients often complain of headache, dizziness, nausea, exhaustion, severe swelling of the affected parts of the body and fever. However, this is very rare. A doctor should be contacted in this case to stop the infection from spreading further.
Read more about this under: Symptoms of blood poisoning


Unless the black fly has transmitted any other disease, only the itching and pain need to be treated. For this purpose, even if it is difficult, the bite site should not be scratched if possible. Bacteria and other toxins are carried (deeper) into the wound via scratching, which can lead to severe infection. It is best to disinfect the sting to prevent infection.

Cool water or ice helps against the itching. Certain home remedies, such as lavender, lemon oil or ribwort juice, are good for calming itching and fighting swelling and redness. In the pharmacy there are also many other preparations.

If the itching and pain have not gone away after a few days, a doctor should be visited. A decision is then made as to whether an antiallergic agent or, due to a bacterial infection, an antibiotic should be used. In addition, anti-inflammatory pain relievers such as ibuprofen or diclofenac can also be used.


Ointments are often used to treat mosquito bite injuries, as they have a good local effect and there are few or hardly any general side effects.
Most of the drugs that are used here, such as antiallergics, antibiotics, diclofenac and cortisone, can be conveniently administered as an ointment. There are also some products in the pharmacy that calm itching and have a cooling effect. They are also given as an ointment for mosquito bites.


Cortisone is a very effective drug against inflammation and irritation. It is particularly popular as an ointment to be applied directly to the diseased area of ​​skin, especially when the skin is injured or infected. In this way, it quiets the irritation particularly quickly and has hardly any side effects that relate to the rest of the body. Still, a doctor should make the decision to use cortisone as it is not suitable for prolonged use on the skin.

When do you need antibiotics?

Antibiotics are useful if the wound has become infected with bacteria or the blackfly has transmitted Lyme disease bacteria. A doctor will then decide whether an antibiotic ointment or even antibiotics should be given as a tablet.
It is rarely necessary to give the antibiotics directly into the vein as an infusion. A Lyme disease infection would classically be through a "Erythema chronicum migrans" detect. This is a reddening that spreads outwards around the bite site, but becomes paler in the center over time.

How can you prevent the black fly bite?

Good prevention against the black flies bite is the best strategy to avoid inflammation and allergies in the first place. In addition, one should avoid the breeding places of the mosquitoes, i.e. flowing waters. In addition, long clothing protects against the bites of insects. There are also mosquito repellants, such as essential oils such as citrus or eucalyptu or special anti-mosquito sprays. They keep the black flies away for a few hours.

Find out more at: Mosquito repellent

Which doctor treats a mosquito bite?

As a rule, the uncomplicated or slightly infected bite of the black fly and any allergies that occur are treated by a dermatologist. If there is a deeper infection with wound healing disorders, these can be treated by a surgeon. Only in the case of a transmission of Lyme disease or “ochocerciasis” should a neurologist or tropical medicine doctor be brought “on board”.

Occurrence of the black fly

The black flies family occurs in around 200 species worldwide. More than 50 of these species can be found in Germany. However, transmission of "onchocerciasis", which can lead to "river blindness", has so far only been observed in tropical regions. In contrast, native species of the black fly transmit borreliosis in some cases.

Learn more about

  • Symptoms
  • Treatment of borreliosis


The duration of a black fly bite is difficult to estimate. It depends to a large extent on how the resulting wound is kept clean, how fast the wound healing takes place and how much a patient is prone to allergies and severe infections.
It is very rare for these complications to occur and a black fly bite does not heal within a few days without consequences. If this is not the case and there are other symptoms such as pain or pus formation, a doctor should be consulted.

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