Butterflies have long straw-like mouthparts (see the black structure in today’s photo). They are called proboscis and suck up e.g. nectar from flowers. When the proboscis is not in use, it is curled up tightly below the head of the butterfly (see previous photo).
The proboscis is made of two separate halves. They zip together when in use. The butterfly uncoils the proboscis, using muscles and hydrostatic pressure, and inserts it into the liquid. A hollow canal within the proboscis then acts like a straw, using capillary action and suction.
Butterflies also use their proboscis to sip moisture and minerals from puddles and to consume liquids from rotting fruit.