title: Paradox of the drinking-straw model of the butterfly proboscis.
abstract: Fluid-feeding Lepidoptera use an elongated proboscis, conventionally modeled as a drinking straw, to feed from pools and films of liquid. Using the monarch butterfly, Danaus plexippus (Linnaeus), we show that the inherent structural features of the lepidopteran proboscis contradict the basic assumptions of the drinking-straw model. By experimentally characterizing permeability and flow in the proboscis, we show that tapering of the food canal in the drinking region increases resistance, significantly hindering the flow of fluid. The calculated pressure differential required for a suction pump to support flow along the entire proboscis is greater than 1 atm (~101 kPa) when the butterfly feeds from a pool of liquid. We suggest that behavioral strategies employed by butterflies and moths can resolve this paradoxical pressure anomaly. Butterflies can alter the taper, the interlegular spacing and the terminal opening of the food canal, thereby controlling fluid entry and flow, by splaying the galeal tips apart, sliding the galeae along one another, pulsing hemolymph into each galeal lumen, and pressing the proboscis against a substrate. Thus, although physical construction of the proboscis limits its mechanical capabilities, its functionality can be modified and enhanced by behavioral strategies.
authors.affiliation: Department of Materials Science and Engineering, Clemson University, Clemson, SC 29634, USA.
authors.forename: Chen-Chih
authors.initials: CC
authors.lastname: Tsai
authors.affiliation: Department of Materials Science and Engineering, Clemson University, Clemson, SC 29634, USA School of Physics, Georgia Institute of Technology, Atlanta, GA 30332, USA.
authors.forename: Daria
authors.initials: D
authors.lastname: Monaenkova
authors.affiliation: School of Agricultural, Forest and Environmental Sciences, Clemson University, Clemson, SC 29634, USA.
authors.forename: Charles E
authors.initials: CE
authors.lastname: Beard
authors.affiliation: School of Agricultural, Forest and Environmental Sciences, Clemson University, Clemson, SC 29634, USA.
authors.forename: Peter H
authors.initials: PH
authors.lastname: Adler
authors.affiliation: Department of Materials Science and Engineering, Clemson University, Clemson, SC 29634, USA kkornev@clemson.edu.
authors.forename: Konstantin G
authors.initials: KG
authors.lastname: Kornev
mesh_terms: D000825:Animal Structures / Q000033:anatomy & histology / Q000502:physiology / Q000648:ultrastructure; D000818:Animals; D002080:Butterflies / Q000033:anatomy & histology / Q000502:physiology* / Q000648:ultrastructure; D005247:Feeding Behavior; D008855:Microscopy, Electron, Scanning; D008954:Models, Biological; D010539:Permeability; D011312:Pressure
keywords: Butterfly feeding; Hagen–Poiseuille flow; Lepidoptera; Suction pressure; Wicking phenomena