Butterflies and Fluid Dynamics

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In seriously gross news, I just found out that butterflies and moths use their proboscis not only to sip nectar from flowers, but also to sip more complex and viscous fluids, like the blood and tears of animals (that should give my sister nightmares for the rest of the month).  Researchers out of Clemson University are attempting to mimic the proboscis by creating tiny probes that could siphon liquid out of single cells for medical testing, diagnosis, and treatment.  This appendage is a great choice because it is able to perform multiple tasks beyond liquid acquisition: it is also a sensory organ, it can coil and uncoil, and it is self-cleaning.  The ultimate idea behind this project is the eventually allow doctors to pluck out a single defective gene from a cell and replace it with a good one.  While this is an ambitious goal, this work does provide some fantastic new information about adapting insect physiology into medical technology.

The researchers, in a team comprised of materials scientists and biologists, first attempted to describe the fluid acquisition mechanism of butterflies.  Believe it or not, this has been a hotly debated topic in entomology.  A typically used model is the "drinking straw model", which is flawed because it requires us to assume that the proboscis is a straight tube, which it is not.  To test the validity of this model, the authors looked at the permeability and flow of the drinking region of the proboscis.

There's a lot of math in this paper, some of which was later corrected, but the gist of this paper is: according to the math, butterflies and moths shouldn't be able to drink from their proboscis.  Because of its shape and structure, the pressure differential required for the suction to work is greater than 1 atm.  For context, no vacuum pump can produce a pressure differential greater than 1 atm on Earth.  The authors suggest that the insects use a behavioural strategy to overcome this problem, by altering the taper, length, pore size, and placement of the proboscis, and how they use it, ultimately making it act like both a sponge and a straw. 



Monarch butterfly proboscis under
a scanning electron microscope

This is just the first phase of the study, the next phase will involve studying the formation of the proboscis during the metamorphic stage.  Afterwards, researchers will study how insects are able to get their proboscises into and out of animal tissues without getting them covered in organic material, including skin and blood cells and bacteria. 

What is especially exciting about this research is the awesome example of what happens when scientists get out of their silos and start collaborating across disciplines.   This study was the result of collaboration between biologists and engineers, to look at the same problem from different perspectives and come up with a meaningful solution.