From Nookipedia, the Animal Crossing wiki
The Agrias Butterfly (ミイロタテル, Miirotateru) is a rare insect in the Animal Crossing series. It can be found in summer, between the months of June and September. It can be sold for 3,000 bells. It is different to other butterflies in the game, using speed and agility to avoid being caught in a net, while others fly slowly.
Donating to the Museum
In Wild World
"The agrias butterfly is said to be quite an agile flier. I'm shocked you snared one! Yes, rather impressive! I know for a fact that I could never do it, wot! Or, to be more accurate, catching one would never even cross my mind...Fleeing from one...That I might do!"
In City Folk
"I must commend you for catching this particular type of butterfly! The agrias butterfly's atypical flight pattern has earned it the nickname "King of the Butterflies." It's such a swift flier that most enthusiasts who attempt to catch one rely on traps, eh wot? I daresay I'd lose a race with this flittering thing... Though I'd likely pass out from mortal revulsion first."
It can found flying in the bottom terrace by the entrance of the insect room, with other butterflies.
In New Leaf
Upon being donated, the butterfly can be found in the first room of the bug exhibit resting on flowers with the other butterflies. The exhibit has this to say about the Agrias Butterfly:
"Agrias butterflies are argued to have the most beautiful wings of all butterfly species. They're capable of flying quite fast, making them more difficult to catch than a number of their peers. Their wings sport three colors - red, blue, and black - but many have different patterns and shapes."
The family, Nymphalidae or "Brush-footed butterflies", gets this name from the forelegs of the adults, which are small and hairy, and resemble small brushes. However, these forelegs are not used for walking.
Names in other languages