This just in from the AP:
Researchers in Denmark report that the Alcon blue butterfly has
managed to produce larvae with a chemical coating similar to that of
the local Myrmica rubra ants. The butterflies deposit their
larvae on marsh gentian plants where exploring ants find them, identify
the chemical coating, and take the butterfly larvae back to the ant
colony and feed them until they grow up and leave.
Read more at New Scientist. The photo comes from David Nash, one of the researchers.