Neither fairy nor fly

world's smallest insect, a parasitoid wasp

In reference to being either good or bad, J. M. Barrie wrote in Peter Pan that fairies must be one or the other, because “being so small they unfortunately have room for one feeling only at a time.”  Entomologists have their own version of fairies, but theirs are very much real.  And, whether they are good or bad is a matter of perspective.  But Barrie was right about one thing:  they are very small indeed.

Dicopomorpha echmepterygis male, paratype, ventral. 52 habitus 53 head + prothorax + procoxa 54 apex of gaster 55 mesosoma + base of most legs and metasoma. Scale line = 20 μm, except Fig. 52 = 50 μm. Source: Wikipedia ex Huber and Noyes, 2013, Journal of Hymenoptera Research 32: 17-44. CC by 3.

Let’s begin with their common name ‘fairyflies.’  These insects are neither fairies nor flies.  Although there are no enforceable rules about common names, tradition dictates that when an insect is a true fly that its common name is written as two words.  Thus, we have house flies, crane flies, bot flies and so forth.  And when a common name incorporates the word fly for an insect that does not belong to the order Diptera, it is written as one word.  This gives us dragonflies, butterflies, and fireflies which are odonates, lepidopterans, and beetles respectively.  And it gives us fairyflies which are teeny, tiny wasps.

Any species of the Hymenopteran family Mymaridae is known as a fairyfly.  So far, there are about 1,400 species of them in both temperate and tropical latitudes.  Among mymarids are both the smallest insect capable of flight and the smallest insect of all.  How small is the smallest insect?  Really small.  It is a mymarid that is 139 µ in length.  A micron is one millionth of a meter or one one-thousandth of a millimeter.  For comparison, the common single-celled protist Paramecium caudatum may be 330 µ long and species of the single-celled trumpet protist genus Stentor may be 1 mm or 1,000 µ in length!

Let’s put it another way.  Four males of Dicopomorpha echmepterygis, lined up end to end, would just about span the width of a typical period at the end of printed sentence.  This, smallest of all insects, was discovered in Illinois.  Males are smaller than females.  They have long legs, especially the hind pair.  They are eyeless and wingless and their mouth externally appears as nothing more than a small, round hole.  Their antennae are reduced, too, appearing as a pair of giant ears.  Like all mymarids, they are parasitoids on the eggs of other insects.  They never leave the host egg, mating with one of their sisters in situ.

Edward Mockford discovered this microscopic wasp while studying the barklouse Echmepteryx hageni.  Fairyflies showed up unexpectedly in his cultures.  When he dissected host eggs, he found both fully developed fairyflies.

For almost everyone aside from a few expert hymenopterists, it can be said that we have all been close to fairyflies but have never knowingly seen one.  Their minute size makes them effectively invisible to most of us, yet they are among the most common chalcidoid wasps.  Wings for the many mymarids which have them are slender with fringes of long bristles.

Another mymarid, discovered in the Hawaiian Islands, Kikiki huna, is the smallest flighted insect — there being a distinction between insects capable of flight under their own power and those which glide and float on air waves.  Its name, among the most fun to pronounce, is derived from two Hawaiian words both meaning “tiny bit.”

Another wonderfully named fairyfly is Tinkerbella nana, the genus named for the fairy from Peter Pan and the specific epithet for the dog nana in the children’s story which, incidentally, also aligns with the Greek word for dwarf, nanos.  Entomologists Huber and Noyes, the scientists  responsible for the discovery of Tinkerbella and Kikiki, have provided a fascinating discussion of reasons for a lower limit of just how small an insect can be and still remain a functioning animal — but that’s a story for another day.

After centuries of taxonomy, we have only begun the process of discovering the limits of diversity among species.  For those willing to see it, the biosphere is overflowing with wonders of the unknown, with record-breaking new species around every corner.  We should conserve biodiversity because ecological services sustain us and because it is simply the right thing to do, but  also to nurture the human spirit, to assure we can always indulge our innate urge to explore and to discover.  To preserve our sense of childlike wonder, we should repeat a line from Peter Pan to our planet’s biodiversity: “Just always be waiting for me.”

References

Huber, J.T. and J.W. Beardsley 2000. A new genus of fairyfly, Kikiki, from the Hawaiian Islands (Hymenoptera: Mymaridae).  Proceedings of the Hawaiian Entomological Society 34: 65-70.

Huber, J.T. and J.S. Noyes 2013. A new genus and species of fairyfly, Tinkerbella nana (Hymenoptera, Mymaridae), with comments on its sister genus Kikiki, and discussion on small size limits in arthropods.  Journal of Hymenoptera Research 32: 17-44.

Mockford, E. L. 1997. A new species of Dicopomorpha (Hymenoptera: Mymaridae) with diminutive, apterous males.  Annals of the Entomological Society of America 90: 115-120.