A proboscis ( or ) is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In invertebrates, the term usually refers to tubular mouthparts used for feeding and sucking. In vertebrates, a proboscis is an elongated nose or snout.
First attested in English in 1609 from Latinproboscis, the latinisation of the Greek (proboskis), which comes from (pro) "forth, forward, before" + (bosko), "to feed, to nourish". The plural as derived from the Greek is proboscides, but in English the plural form proboscises occurs frequently.
Scanning electron microscopy of proboscis of an Acanthocephala
The Acanthocephala or thorny-headed worms, or spiny-headed worms are characterized by the presence of an eversible proboscis, armed with spines, which it uses to pierce and hold the gut wall of its host.
Lepidoptera mouth parts
The mouth parts of Lepidoptera mainly consist of the sucking kind; this part is known as the proboscis or 'haustellum'. The proboscis consists of two tubes held together by hooks and separable for cleaning. The proboscis contains muscles for operating. Each tube is inwardly concave, thus forming a central tube up which moisture is sucked. Suction takes place due to the contraction and expansion of a sac in the head. A specific example of the proboscis being used for feeding is in the species Deilephila elpenor. In this species, the moth hovers in front of the flower and extends its long proboscis to attain its food.
A few Lepidoptera species lack mouth parts and therefore do not feed in the imago. Others, such as the family Micropterigidae, have mouth parts of the chewing kind.
The study of insect mouthparts was helpful for the understanding of the functional mechanism of the proboscis of butterflies (Lepidoptera) to elucidate the evolution of new form-function. The study of the proboscis of butterflies revealed surprising examples of adaptations to different kinds of fluid food, including nectar, plant sap, tree sap, dung  and of adaptations to the use of pollen as complementary food in Heliconius butterflies. An extremely long proboscis appears within different groups of flower-visiting insects, but is relatively rare.
^Charles A. Triplehorn and Norman F. Johnson (2005). Borror and Delong's Introduction to the Study of Insects (7th edition). Thomson Brooks/Cole, Belmont, CA. ISBN0-03-096835-6
^Krenn HW, Kristensen NP (2000). "Early evolution of the proboscis of Lepidoptera: external morphology of the galea in basal glossatan moths, with remarks on the origin of the pilifers". Zoologischer Anzeiger. 239: 179-196.
^Krenn HW, Zulka KP, Gatschnegg T (2001). "Proboscis morphology and food preferences in Nymphalidae (Lepidoptera, Papilionoidea)". J. Zool. Lond. 253: 17-26. doi:10.1017/S0952836901000528.
^Knopp, M. C. N.; Krenn, H. W. (2003). "Efficiency of fruit juice feeding in Morpho peleides (Nymphalidae, Lepidoptera)". Journal of Insect Behavior. 16: 67-77. doi:10.1023/A:1022849312195. S2CID33428687.