The beetle Scydosella musawasensis has been declared the world's smallest free-living insect. Besides the cuteness factor, the announcement tells us something about how small insects can actually be. The size is as small as some unicellular organisms.
S. musawasensis, a type of featherwing beetle, was first collected in 1955 in Nicaragua, but not scientifically described until 1999. Scientists were not aware of subsequent examples until recently and it was not known if the species even survived.
Among the specimens Polilov examined, one was just 0.325 millimeters (0.014 inches) long. This is almost twice as long as a Dicopomorpha eschmepterygis, which has been measured at just 0.139 millimeters (0.005 inches), but D. eschmepterygis – like other extra-small species – is a parasitic insect, unable to survive independently. Reports have been made of smaller free-living insects, but Polilov says these have turned out to be errors.
Measuring the world's tiniest insects is a lot harder than non-entomologists might expect. Polilov explains that many are embedded in preparations, making them difficult to measure. In this case, specialized software and a scanning electron microscope were required to get precise enough measurements to confirm S. musawasensis's status as the record holder.
Polilov's record-breaking specimen was not an outlier. The average beetle measured was just 0.338 millimeters and the largest example of S. musawasensis he found was 0.352 millimeters. All were around 0.1 millimeters wide (0.004 inches).
“The smallest insects have recently attracted considerable attention as models for studying animal miniaturization, since they are among the smallest metazoans and since many morphological features unique to them and resulting from their extremely small size have been described,” Polilov writes.
In a paper published earlier this year, Polilov described the “considerable reorganization of structures” seen in insects that have taken miniaturization to its limit. Studying these examples allows us to explore biology at the extremes.
Beetles (Coleoptera) are the most numerous order of animals in terms of species numbers, partly because they seldom go extinct. The creator, it seems, really is fond of beetles, including very small ones.