#19 The main danger of these insects is that they are carriers of infectious diseases such as anthrax, polio and others.
Agriculture suffers irreversibly from these insects. The animal's stamina, milk yield and so on become lower.
#20 It is necessary to immediately consult a doctor if the temperature rises after a horsefly bite.
Of course, everything is beneficial, even horseflies. They are included in the diet of birds and fish. But without them, as well as without other living organisms, the cycle of life in the surrounding world is impossible.
They are an important part of the food chain in nature. So reducing the number of these insects will lead to an imbalance.
And by the way, horsefly and gadfly are completely different insects. Even though they are equally intrusive.
To protect yourself from these unpleasant insects, you should know their habits and try not to come to their dense habitats.