In fact, even harmful animals and reptiles have a purpose to serve. It is only because of our lack of understanding that we may not understand what the purpose is. There was a king who was sitting in his court with all splendour and pride.
A fly came to sit on his nose and he waved it off. The fly was however stubborn and as many times as the king chased it away, it came back each time.
The king finally said, "I don't know why Allaah has created this fly because it gives only trouble!"
A pious man sitting in the court remarked, "But it does have a purpose to serve. Allaah has created it to correct the crooked thinking of tyrants like you. It is there to teach you that despite what you think, you do not even have the ability to stop a fly from troubling you."
The first thing we learn from this is that we should never underestimate the value of anything because everything has importance.
The second thing we learn is that we must never have pride because Allaah does not like it at all and will punish a person for it.
We must also never complain about the creation of anything because this is actually objecting to what Allaah has created. Similarly, we must also never tease anyone for being fat, short, thin, etc.
We must be careful never to joke about any person's colour, eyes, nose, etc r about the weather being too hot, too cold or rainy. Allaah does not like these complaints, so we must be very careful about how we speak.