Proboscis musculature in the butterfly Vanessa cardui (Nymphalidae, Lepidoptera): settling the proboscis recoiling controversy

The proboscis of Vanessa cardui (Nymphalidae) contains two basal galeal mus cles and two different series of numerous oblique muscles. Both muscle seri es extend from the proximal region up to the tip-region; the individual mus cles of each series run a constant course throughout the proboscis. In cont rast to other butterflies, the knee bend region does not have additional ty pes of muscles. The analysis of shock-frozen proboscises reveals that the d orsal wall is arched outwardly in the uncoiled, feeding position whereas in the coiled, resting position the dorsal proboscis wall is flat or concave. This results in a significantly greater cross-sectional area due to the si gnificantly greater dorso-ventral diameter in uncoiled proboscises. After f reezing the proboscis in its distal region, it can still be uncoiled, howev er, it cannot be fully recoiled. These morphometric and experimental result s indicate that the oblique proboscis muscles are responsible for recoiling the proboscis to the resting position.