You see a butterfly.
Notes
The red butterfly is the fastest of all three and the most rare to find.
Their dead bodies can be put in a Butterfly Conservation Kit to be used in The Explorer Society Quest.
Abilities
None.
Damage Taken From Elements
Physical 
Death 
Holy 
Ice 
Fire 
Energy 
Earth 
Location
Yalahar, Tiquanda, the Shattered Isles, Liberty Bay, Carlin Surroundings (near the Tired Tree) and some other places.
Behaviour
A butterfly does not attack. A butterfly will retreat at 2 (100%, full) health.
Strategy
Just attack. Since it doesn't drop any loot, you should just leave it alone unless it gets in your way.