Does size matter?

I saw a great image today got me ruminating about size in insects, the measurements we use for size, and the concept of size in general.  The picture below appeared recently in combination with a news story and is of one of the smallest insects in the world.  It is placed, for size reference, next to an amoeba and a Paramecium for scale.  You remember amoebas and Parameciums from elementary or middle school science classes right?  Found in pond water by the kajillions, but only really visible under a microscope, these microorganisms were many a school child’s first introduction to the world of the too-small-to-be-seen.

smallest insect and Paramecium_sm

Two famous microbes, the amoeba and the Paramecium, next to a fairy wasp, Megaphragma mymaripenne, one of the smallest insects. Credit: Alexey Polilov

The fairy wasp is widely referred to as the smallest insect. Fairy wasps are parasites on the eggs of other insects.  The supposedly smallest fairy wasp species is Dicopomorpha echmepterygis, a Costa Rican species that parasitizes the eggs of a barklouse–an insect that itself is barely visible to the untrained eye.  The males of Dicopomorpha echmepterygis are thought to be no more than 139 micrometers long–smaller than a Paramecium.

The wasp in the picture, at 200 microns-long,  is slightly larger than Dicopomorpha, and was published to illustrate a recent study that shows that small size comes at a cost.  It seems that Megaphragma mymaripenne goes to the extreme length of shedding nuclei in its nerve cells to help achieve its minute size.  That’s the insect equivalent of a filed down toothbrush for a backpacker, or a sprinter shaving his head to get a faster speed on the track.  You’ve got to admire their commitment.

Just like the unfathomable distances of space, measurements of smallness are difficult for most of us to comprehend.  If you are reading this at a desk, search around and look for a ruler.  Now look at the metric side of the ruler.  The smallest markings there are millimeters (mm), 1/1000ths of a meter (39 inches for us unenlightened Americans).  Of the insects and mites that come across my desk for identification, the smallest that people see and send in are usually in the 1-2 mm range.  These include some mites, thrips, booklice, and even a few very small beetles.  The periods at the end of these sentences on your computer screen are about 1/3 to 1/2 of a millimeter.

A micrometer (also called a micron) is 1/1000 of one of a millimeter.  So fairy wasps are about 1/5 the length of a millimeter.  Pretty small.  That’s about 1/3 the width of the period at the end of this sentence.  A human hair, for comparison, averages about 100 microns in diameter (1/10 mm).

I’m battling a cold at the moment, caused by a virus that is probably only about 20 nanometers across.  A nanometer is 1/1000th of a micron, or one one-millionth of a millimeter.

Obviously small doesn’t mean unimportant.  Many of the world’s tiniest insects have extremely important roles in the ecosystem.  In the case of fairy wasps, their role is helping control other tiny insects.  Many of our most important beneficial insects are small–1/1000th the size of a lady beetle or less.

I guess the point of all this is that size does not equal importance.  Science is showing us that the tiny things in this world, that so many of us seem to think beneath our dignity, are actually beyond our comprehension.

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