Butterflies and moths use their slender probosci to sip nectar, plant sap, etc. Let the radius be 30 μm, and the length be 1.4 mm. The visocsity varies with the sweetness of the nectar, but you can take it as around 2 mPa-s. How fast would you predict these lepidoptera can pull in their food? (Think about the Pressure difference, which we haven't said anything about.) How does this compare with measured rates of flow of around 3 x 10-10 m3/s? The difference turns out to suggest interesting different biology