When I looked closely at this photo of the hoverfly Rhingia campestris feeding on a primrose I noticed that ....
..... when it withdrew its tongue the tip of the proboscis sometimes split into two, and then closed up again. I've noticed this before in nectar-feeding insects like bee-flies and suspect that it may be the insect's way of clearing blockages that occur in the capillary tube formed by the proboscis.
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