What Are The Harmful Effects Of Insects To Human?

Mostly, insects are more of a nuisance than a harm. Most may bite a human and cause itching and rashes. These are not harmful as such but they are bothersome.
However, some insects can actually harm humans or play a part in harming humans. Harmful insects are those which are poisonous when they bite. Examples include, fire ants, harvester ants, brown widow spiders, the hobo spider and the brown recluse spider.

Besides that insects may play a part in transmitting various diseases to humans. A very common example is the house fly. When it comes into contact with fecal matter, it (along with all the bacteria on it) sticks to its feet. Thus, when the fly next sits on something, it leaves a trail of fecal matter and its bacteria behind. If it comes into contact with food that we consume, we may ingest harmful bacteria. House flies are a common agent for cholera.

Other insects may act as vectors for a disease. This means they carry a pathogen in them. When they bite, this pathogen enters human blood, thereby causing disease.
Some insects and the diseases they may cause by acting as vectors are:

  Insect                   Disease
Lice                          Typhus
Anopheles mosquito   Malaria
Aedes mosquito         Dengue fever