your guppies are all male. They have probably reached sexual maturity and because there are no females in the tank, they are taking their frustrations out on each other by being aggressive and frisky.
Add some female guppies - approx 14 (a ratio of 1 male to 2 females) - and they'll calm down.
Incidentally, do you keep your guppies in a planted tank? Once you add females, there will be a fry explosion and the plants will give the fry hiding places.