Structural architecture of a butterfly’s proboscis: more than a simple drinking straw

Matthew S. Lehnert

This SEM image of a butterfly’s proboscis represents a current collaborative effort between engineers and biologists to use the proboscis as a model to develop microfluidic devices capable of acquiring minute amounts of liquid for medicine and molecular research. Previous work has suggested the proboscis functions as a drinking straw, but our recent effort has showed that capillary action is an important component. This SEM image of a red-spotted purple butterfly’s proboscis highlights the small spaces used to acquire liquid by capillary action into the proboscis before the pump in the butterfly’s head transports the liquid to the gut.

Structural architecture of a butterfly’s proboscis: more than a simple drinking straw by Matthew S. Lehnert The top and bottom margins of this picture represent composite SEM images (150X magnification) of the apical 20% of the red-spotted purple butterfly’s proboscis. A butterfly’s proboscis is used to feed on fluids from sources such as floral nectar and rotting fruit. A butterfly’s proboscis is composed of two elongated maxillary galeae (modified mouthparts) that unite into a tube upon emergence from the chrysalis. The linking structures used to merge the galeae are called dorsal and ventral legulae. Although the ventral legulae (not seen here) are tightly interlocking hooks, the dorsal legulae only overlap. In this species, the dorsal legulae of the apical portion of the proboscis become modified (tooth-like) and are used for acquiring fluids when it is laid on the butterfly’s food source. The large structures on the border of the proboscis (sensilla styloconica) are used for sensing sugars. The middle image highlights the unique tooth-like dorsal legulae (800X magnification). The proboscis has been assumed to function as a drinking straw; however, we have shown that this versatile structure also is capable of capillary action. These specialized legulae are used to enhance the sponging of liquids into the food canal of the proboscis by capillary action, which is then transported to the gut by a sucking pump in the butterfly’s head. The dorsal legulae may also assist in rasping rotting fruit to gather greater amounts of liquid. We are using these results to produce a microfluidic device capable of taking in minute amounts of liquid, similar to a butterfly’s proboscis. All images were taken with a Hitachi TM3000 scanning electron microscope at the Clemson Microscope Facility.
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