Butterfly anatomy may help scientists probe cells

One of my favorite treats is a butterscotch malt. However, trying to drink one through a straw can be difficult because of the viscosity of the concoction.

It is interesting to note that the smaller the diameter of the straw, the more suction it takes to draw fluid into it. So when ordering butterscotch malts, it is best to ask for the largest-diameter straw.

Of course, most places only have one diameter of straw, so perhaps you should carry a supply of large-diameter straws of your own.

So consider the difficulty a butterfly, moth or bee might have in obtaining its own version of butterscotch malt: flower nectar or fruit juice. They have to obtain their liquid food through a mouthpart called a proboscis that has a very tiny diameter. (This is similar to, but structurally different from, Jimmy Durante’s.)

A butterfly’s proboscis looks outwardly like a straw — long, slender and used for sipping. The proboscis varies somewhat in diameter among different insect species, but it is generally close to about 50 micrometers (or one-twentieth of a millimeter). I don’t think you can buy straws with that small of a diameter. In the Monarch butterfly, the proboscis is about 13 millimeters long.

Inside the butterfly’s head, this straw-like proboscis is attached to a muscular suction pump.

When these muscles contract they expand the size of a compartment, much like pulling on the piston in a syringe.

Or like your cheek muscles do when sucking on a straw. This expansion reduces the inside pressure relative to the atmospheric pressure, forcing liquid into the proboscis.

At these tiny diameters the viscosity of these fluids would require enormous amounts of pressure to be sucked up. Estimates based on engineering hydraulic formulas suggest that the pressure could be greater than one atmosphere. That is greater than any vacuum pump at these sizes could apply.

This pressure also might be more than the walls of the proboscis could withstand and the tube would collapse. Another problem is that when fluids are placed under less pressure than atmospheric pressure, they disassociate into a gas.

At these suction pressures, the nectar would boil into a gas, thereby reducing the pressure and the nutrient value of the food.

Konstantin Kornev of Clemson University recently published a paper that shows Monarch butterflies (Danaus plexippus) may use capillary action to fill the proboscis and use a pumping mechanism only to empty the proboscis into the intestinal tract. Electron micrographs of the proboscis of the butterfly show that it resembles a rolled-up paper towel.

There are tiny grooves that can be modified in diameter by a zipper-like mechanism attached to muscles along both the top and bottom surfaces.

By slightly modifying the diameter of the central groove, the liquid is pulled up the tube by capillary action, somewhat the way fluid is pulled into a paper towel.

The fluid adheres along the edges of the food channel, and more liquid clings to that liquid in the same way that water clings to water at the edge of a glass container and forms the meniscus.

This process is not nearly as affected by viscosity as pumping. In fact, if there is a high capillary attraction within the fluid, which often occurs with increased viscosity, thicker nectar actually would aid feeding.

Kornev hopes to borrow the tricks of this piece of insect anatomy to make small probes that can sample the fluid inside a cell.

He has been awarded a National Science Foundation grant to develop such artificial probes made of nanofibers.

This would enable someone to examine cell cytoplasm taken from a living cell. Present methods require the destruction of the cell membrane to obtain cell fluids.

I’m wondering if a more practical application might not be to see if nanofibers couldn’t reduce the effort required to drink a butterscotch malt?

Gary McCallister is professor of biology at Mesa State College and CEO of Flaming Moth Productions.


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