Figure 1.

Structural features and wettability of the lepidopteran proboscis. (a) Water droplet placed on the proximal region of the proboscis of Papilio glaucus results in a clam-shell formation, indicating hydrophobicity, whereas fluid on the submersed distal region of the proboscis has a hydrophilic contact angle (inset). (b) The dorsal legulae remain approximately the same width along 90 per cent of the proboscis of Danaus plexippus. Each dorsal legula consists of an upper (ub) and lower branch (lb; insets a,b); the upper branches enlarge in the distal region of the proboscis (inset c). (c) We measured the widths of the upper branch of the legula (lw) and the galea (gw) to demonstrate structural arrangements of brush-tipped and smooth-tipped proboscises (Limenitis arthemis astyanax proboscis on the left, with slight artefactual opening between dorsal legulae of opposing galeae; Danaus plexippus on the right). (d) Schematic of a cross section of the proboscis showing two C-shaped galeae with lateral and median intrinsic muscles (lm and mm, respectively), nerves (ne) and tracheae (tr). The galeae are held together by overlapping dorsal legulae (dl) and interlinking ventral legulae (vl), forming a food canal (fc). (Online version in colour.)