Proboscis

What is a proboscis

Proboscis (Latin proboscis) is a specialized mouthpart of an adult butterfly adapted for consuming liquid food. It is a flexible hollow tube formed by two fused galeae — modified parts of the lower jaw (maxilla).

At rest the proboscis is coiled in a tight spiral under the butterfly's head. When feeding, it straightens and is inserted into a flower or other food source.

How the proboscis works

The principle is suction: powerful pharyngeal muscles create a vacuum, and liquid rises through the tube. The proboscis itself does not contract — it is only a flexible guide.

Proboscis length varies greatly among species:

• In most day-flying butterflies — 1–3 cm
• In some hawk moths (nocturnal) — up to 30 cm (record — Xanthopan morganii praedicta)

Charles Darwin predicted a Madagascan orchid with a 30 cm nectar spur — and a corresponding pollinator with the same proboscis length. Both were found 40 years later.

Proboscis and feeding

The proboscis allows consumption of:

• Flower nectar
• Sap of overripe fruit
• Liquid from damp soil (puddling)
• Hemolymph from insect wounds (in some tropical species)

Species with a rudimentary proboscis

Some butterfly species do not feed at all as adults — their proboscis is underdeveloped or fused. They live on reserves accumulated as caterpillars. Such butterflies live 2–5 days, only long enough to mate and lay eggs.

More on feeding — in the article what butterflies eat.