I've never seen one in person, but I think this is a Cuckoo Wasp. 3 things lead me to 'guess' this: the small size of your insect...the color....and that very long stinger (for its size).

Cuckoo wasps come in other metallic colors, but this is typical. They are parasites of bees and wasps of all kinds, and when they aren't parasitizing, they are stealing from them.