There are a big veriety of insects, but i want to speak about fly. It's one of wiedly spread insect in the world they live everywhere: in our houses, in parks e.t.c
Of course they looks ugly, but they make useful things such as collecting rubbish. But also this insects have disadvantages too and this disadvantages are really very serious! The mail problem of them it's their ability to spread infections.
In conclusion i want to add that we need to overcome problems which connected with insects, but we mustn't kill them, because insects also make a lot of usefull things for us.