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Have you ever watched a tiny red ant scurrying through the backyard only to be astounded that the ant seems like a giant when it walks by some much smaller black ants?  Such observations have always caused me to wonder how small insects could become.  What are the smallest insects out there and just how tiny are they?   The answer is actually astonishing, and, like most good answers it just brings up more questions.  Most entomologists believe the tiniest living insects are the fairyflies, infinitesimally minute parasitoid wasps which live on or inside the tiny eggs of thrips(well, some fairflies also live inside the brains of other insects, but let’s not think about that right now).  Fairyflies are smaller than many single cell organisms like paramecia, amoebas, and euglenas.    Dicopomorpha echmepterygis,  a wasp from Costa Rica, is an astonishing  .13 millimeters in length.   Although many of these wasps fly, they are so tiny that they don’t have conventional wings:  some of the smaller specimens have long cilia-like hairs which they use to row through the air (the fluid dynamics of which are considerably different for creatures so small).

Fairy wasp with single celled organisms under electron microscope

In fact the wasps are so tiny that the millions of individual cells which make up their tissues and organs have to be very miniscule indeed.  In fact, according to physics, the brains of fairyflies should not work.  Many of the neural axons are smaller than 0.1 micrometre in diameter (and the smallest axons were a mere 0.045 μm).  At such sizes, the electrical action of axons should not work properly.   An article on Newscientist describes the basic problem:

 …according to calculations by Simon Laughlin of the University of Cambridge and colleagues, axons thinner than 0.1 μm simply shouldn’t work. Axons carry messages in waves of electrical activity called action potentials, which are generated when a chemical signal causes a large number of channels in a cell’s outer membrane to open and allow positively charged ions into the axon. At any given moment some of those channels may open spontaneously, but the number involved isn’t enough to accidentally trigger an action potential, says Laughlin – unless the axon is very thin.

So how do the wasps continue to fly around and parasitize the eggs of other creatures if the electrical impulses of their brains do not work?  German researchers speculate that the axons of wasp brains work mechanically rather than electrically.  The tiny axons touch each other physically instead of by means of electrical action.  If this is correct it means the wasps are analogue creatures with little clockwork minds!  If they were any larger or more complex, this would not work, but because of their small size and simple drives, they can manage to operate with slow-moving machine-like brains.

Micrograph of a fairyfly (fairy wasp)

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