Bug-type Pokémon are characterized by their fast growing, they don't take long to evolve. Bug-type Pokémon live mostly (not all of them) in forests, some of them are a little harder to find because they live atop the trees.
From Generation V on, it is known that Bug-type Pokémon are preferred by artists, mostly because they have beautiful colors and have a stoic and cheerful character. It can be said that Bug-type Pokémon represent the beauty of nature. Many of the bug-type pokemon evolutions are similar to the life cycles of insects like that of beetles and butterflies; i.e the first stage like larvae, second like pupae, then its final evolution into its mature, adult form.
They're strong against the Psychic type because they represent a common fear affecting the psychology of the mind. Further, members of this type often do not have the mental capacity to be very susceptible to mental manipulation.
They're strong against the Grass type because members of this type commonly consume plants and similar organic material.
They're strong against the Dark type because members of this type are well adapted to operating in darkness and do not have the mental capacity to fear the dark.
They're weak against the Flying type because many members of this type are ground dwellers, vulnerable from attacks from up above. Further, many members of this type are commonly preyed upon by Flying type members.
They're weak against the Fire type because fire consumes the exoskeletons endemic to members of this type rather easily, and where fire is both a bane and repellent to insects, either keeping them at bay with its increasing heat or drawing them into its flame with its light.
They're weak against the Rock type because the strength of their exoskeletons rarely can endure the weight or impact of rock or stone.
They're resistant against the Ground type because many bugs like worms live inside the ground and many of them eat it.
The Ghost type is resistant to them because members of this type cannot easily transcend the spiritual barrier members of that type hide behind in order to attack them.
The Fighting type is resistant to them because the strength of their exoskeletons rarely can endure the weight or impact of physical blows.
The Fairy type is resistant to them because many fairies live along bugs.
The Poison type is resistant to them because members of that type have developed natural resistances to poisons, rendering many poison-based bug attacks ineffective. This type was vulnerable to Poison type attacks in Generation I, but this weakness was possibly removed due to members of this type's rapid adaptation to poisonous material.