Important among the insects which spread various diseases through bites are mosquitoes, tse tse flies, ice, rat fleas, bed bugs etc. when these insects bite some diseased person and suck the blood, the germs of his disease pass into the bodies of the insects.

When these insects bite a healthy person, they pass on to him the germs of that disease along with the saliva. These germs infect the healthy person and make him sick.

Malaria is caused by the bite of anopheles mosquitoes, and the dangerous sleeping sickness due to the bite of tse tse flies. Lice transmit typhoid. The rat fleas carry the germs of plague. Bedbugs cause skin diseases. They suck our blood to keep themselves alive.

We wonder how the germs of the diseases are passed into our body while the insects keep on sucking the blood. In fact before sucking the blood, they inject a small amount of saliva into our body to prevent the blood from clotting. By doing so the germs of the disease enter our body along with the saliva.

However, there are some other insects too which sting but do not spread any disease. Among them are honey bee and wasp. Their sting cause intense pain. The stings of these insects are located at the tail end. They are connected to poison glands.

These insects use them as weapons for their self-defense. When they bite us, they inject some poisonous substance into our body. It is this poison that causes swelling on the skin and pain.