Worlds smallest fly discovered

In a paper appearing today, Monday, July 2, 2012, I describe the world’s smallest known fly. It was collected during the TIGER (Thailand Inventory Group for Entomological Resources) project, funded by the National Science Foundation with the grant to Dr. Michael Sharkey of the University of Kentucky and me (as co-PI).

Many stories about small things, especially parasites, quote Jonathan Swift:

“So, naturalists observe, a flea
Hath smaller fleas that on him prey;
And these have smaller still to bite ’em;
And so proceed ad infinitum.”

In this case, the quote is especially apt, because the newly discovered worlds smallest flies are parasites!

The smallest fly in the world is a member of the family Phoridae, and is one of the “ant decapitating flies”. Adult females lay an egg in the body of an ant, and the resulting larva feeds in the ants head, eventually causing the decapitation of its host. Some of these flies are being used to attempt biological control on imported fire ants, and were even featured on an episode of the popular television show “King of the Hill”.

Because these flies usually develop in the head of their host ant, they are smaller than their hosts. One would think that the smallest ants would be therefore immune to these nasty parasites, as their heads are vanishingly small. But the world’s smallest fly is one of these ant killers, and at the astoundingly small body length of 0.4 mm, these flies can probably decapitate ants with heads as small as 0.5 mm. That is pretty close to the smallest size that ants can get!

When we think of animals that are small, usually a fly or a flea come to mind. Let’s forget about fleas; they are comparative monsters at around 1-2 mm in length. But what about flies?

The common house fly is something that we think of as being small. In the world of tiny insects, however, they are virtual Godzillas at a whopping 6 mm.

Many flies are much smaller than this. Fruit flies that you see hovering over overripe bananas, for instance, are about 2 mm long, one third of the size of the “giant” house fly.

Some of the biting flies are much smaller than this. One aptly named family of flies has the common name “no see ‘um”, because of their almost invisibility when they are biting you. These flies are getting really small, usually around 1 mm in length.

The world’s smallest fly is 0.4 mm in length. Here is a microscope slide, 1″ x 3″ size, with the holotype specimen of the fly mounted on it. It’s unimaginably small, smaller than a flake of pepper you shake out of the pepper shaker.

holotype specimen of Euryplatea nanaknihali Brown

Do you see it, within the small circle, to the right and slightly above center?

The world smallest fly doesn’t really look like a fly. It’s one of those weird phorids whose body form we call “limuloid”, after Limulus, the horseshoe crab. It is a defensive body form that allows the flies to live in the ant nest which, based on this body structure, is probably part of the fly’s life. It has short wings, but they are functional sized, so this fly could easily fly from ant nest to ant nest. It also has a sharply pointed tip of the abdomen, indicating that it is a parasitic species.

My research is funded by the National Science Foundation, currently grant No. DEB-1025922.

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation.

12 comments on “Worlds smallest fly discovered

  1. whyevolutionistrue says:

    Hi! Where is the paper appearing, and could you send me a copy? Cool finding. Thanks, Jerry Coyne

  2. Jeff Skevington says:

    Fantastic! Thanks for posting this Brian. For others looking for the paper, it is: Brown, B.V. 2012. Small Size No Protection for Acrobat Ants: World’s Smallest Fly Is a Parasitic Phorid (Diptera: Phoridae). Ann. Entomol. Soc. Am. 105(4): 550-554.

  3. Jeff Bjorck says:

    Congratulations on this amazing find! Truly astounding. Thanks for posting!

  4. Another amazing find Brian, and I can’t wait to read the paper and become more acquainted with this petite parasite!

  5. Great discovery and a very nice paper. I used it to write a Wikipedia article ( about the species which I hope will introduce those to this tiny fly who do not have access to the paper (although I think the PDF version is actually around for free).

    Oh, and I also have some (actually a bunch of) questions relating to this: From the accounts in the press and from your own paper, I was not quite able to understand whether you think E. nanaknihaly does actually paratize Crematogaster rogenhoferi (i.e. the ranges of both species overlap although C. rogenhoferi has not been found at the type locality yet) or if it is just a possible host species of some geographical vicinity.

    You are talking about host fidelity within this group of flies – are you implying that the genus Euryplatea sticks to Crematogaster or do you mean that their closest relatives are also Crematogaster parasites?

    In which way do you relate to Nanak Nihal Weiss? I read that he is an entomolocigal enthusiast from LA, but is he a student of yours or a friend or …?

    I noticed that the Thai Wikipedia also has an article about this species and that it is using one of your photos, apparently without your permission. Rather than implying that you should have it taken off (which you should take into consideration of course), I would like to ask you whether you would like to release a picture of the fly under a creative commons license (cc-by or cc-by-sa) so that we could use it legally at Wikipedia? I think this would make our articles much more attractive for the reader.

    Oh, and is there any alert for readers for whenever youpublish a new original description? I love to write about new species on Wikipedia in real time; however I usually miss the papers when they appear. This is why I love summer slump so much: the newspapers are desperate to publish anything to fill their gaps so that new species get a little more of the attention they deserve.

    • phoridae says:

      Thank you for your interest! I am not sure which species of Crematogaster this fly attacks, but since the African species attacks Crematogaster, it’s a pretty good bet that the Thai one does too.

      The photos in the article belong to the journal, but I have others whose rights remain with me. I will post them in Wikimedia.

      I am going to make new posts to this blog when I describe new species. There is quite a backlog for you, however, just in the phorids!

      Thanks again, Brian

      • Thank you very much, that is very generous 🙂 I could write a short Wikipedia article about you in return, that is, if you want me to (some people prefer not to have an article). And I will at least try to catch up with the species you describe; I guess we’ll need some 100 years just to cover up all the flies currently known. But who knows, maybe we’ll have all known Phorids within the next 20 years 😉

  6. […] week by Brian Brown, and now ranks as the smaller species of fly we know of at only 0.4mm long! Brian has an excellent write up of his discovery over at flyobsession, and he also posted a bonus illustration of the fly which wasn’t in the […]

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