The barbed tips allow it to stay in place while the owner drinks the tears of sleeping birds.
Tear-feeding moths and butterflies are known to exist elsewhere in Africa, Asia and South America, but they mainly feed on large, placid animals, such as deer, antelope or crocodiles, which cannot readily brush them away. But there are no such large animals on Madagascar. The main mammals - lemurs and mongoose - have paws capable of shooing the moths. Birds can fly away.
But not when they are sleeping. The Madagascan moths were observed on the necks of sleeping magpie robins and Newtonia birds, with the tip of their proboscises inserted under the bird's eyelid, drinking avidly (scroll down for images). This was during the wet season, so the scientists think the insects wanted salt, as the local soils are low in sodium.