giant sciarid fly

From a 4 hectare (about 9 acre) patch of cloud forest near San José, Costa Rica, a team of dipterists (fly researchers) have identified over 4000 species of flies, and extrapolations from this collecting suggest that the true total is 7,000 – 8,000. This incredible diversity was the result of the ZADBI project, funded by the US National Science Foundation. A team of talented and dedicated Costa Rican biologists sampled at the site, called Zurquí de Moravia, for an entire year, using several Malaise traps, regular light trapping, hand collecting and other methods. The resulting catch was prepared (mounted, pinned, slide-mounted, labeled) and sent to international experts on various fly families for identification.  The result was an eye-popping number of species, many of them new to science (especially in the families of smaller flies).

Leading the way were the gall midges, or Cecidomyiidae, which were represented by at least 800 species, almost all of the probably undescribed. During the course of the project, cecid expert Dr. Mathias Jaschhof actually described some of the new species, including those that belonged in a new genus he named Zadbimyia in honor of the project (there were 19 of the 22 species of this genus alone at Zurquí).

Second most species rich were the phorids, whose numbers were so large that I am still reeling from the effort of trying to understand their diversity (with help from Maria Wong, Giar-Ann Kung, John Hash, and others). The 400 species we identified is surely just part of what is really there.

There were hundreds of species of other families of flies as well, including lots of strange and wonderful new things. It will be years before we can finish identifying everything, but the project gives us some important insights into tropical Diptera diversity. It is also a testament to how effective a large group of dipterists can be, identifying thousands of specimens of one of the least-known biotas in the world.

I hope to bring you many more details about the results from the project, but for now, here are links to the two recently published papers:

Borkent, A., B. V. Brown, P. H. Adler, D. S. Amorim, K. Barber, D. Bickel, S. Boucher, S. E. Brooks, J. Burger, Z. L. Burington, R. S. Capellari, D. N. R. Costa, J. M. Cumming, G. Curler, C. W. Dick, J. H. Epler, E. Fisher, S. D. Gaimari, J. Gelhaus, D. A. Grimaldi, J. Hash, M. Hauser, H. Hippa, S. Ibáñez-Bernal, M. Jaschhof, E. P. Kameneva, P. H. Kerr, V. Korneyev, C. A. Korytkowski, G. Kung, G. M. Kvifte, O. Lonsdale, S. A. Marshall, W. N. Mathis, V. Michelsen, S. Naglis, A. L. Norrbom, S. Paiero, T. Pape, A. Pereira-Colavite, M. Pollet, S. Rochefort, A. Rung, J. B. Runyon, J. Savage, V. C. Silva, B. J. Sinclair, J. H. Skevington, J. O. Stireman III1, J. Swann, P. Vilkamaa, T. Wheeler, T. Whitworth, M. Wong, D. M. Wood, N. E. Woodley, T. Yau, T. J. Zavortink, and M. A. Zumbado. 2018. Remarkable fly (Diptera) diversity in a patch of Costa Rican cloud forest: why inventory is a vital science. Zootaxa 4402: 53-90

Brown, B.V., A. Borkent , P.H. Adler , D.S. Amorim, K.Barber, D. Bickel, S. Boucher , S.E. Brooks, J. Burger, Z.L. Burington, R.S. Capellari, D.N.R.Costa, J.M. Cumming , G. Curler, C.W. Dick, J.H. Epler, E. Fisher, S.D. Gaimari, J. Gelhaus, D.A. Grimaldi, J. Hash, M. Hauser, H. Hippa, S. Ibáñez-Bernal, M. Jaschhof, E.P. Kameneva, P.H. Kerr, V. Korneyev, C.A. Korytkowski , G. Kung, G.M. Kvifte, O. Lonsdale, S.A. Marshall, W. Mathis, V. Michelsen, S. Naglis, A.L. Norrbom, S. Paiero, T. Pape, A. Pereira-Colavite, M. Pollet, S. Rochefort, A. Rung, J.B. Runyon, J. Savage, V.C. Silva, B.J. Sinclair, J.H. Skevington, J.O. Stireman III, J. Swann, F.C. Thompson, P. Vilkamaa, T. Wheeler, T. Whitworth, M. Wong, D.M. Wood, N. Woodley, T. Yau, T.J. Zavortink, & M.A. Zumbado. 2018. Comprehensive inventory of true flies (Diptera) at a tropical site. Communications Biology (Nature). 

tachinid fly, photo by W. Porras

Questions remain about differentiating greenbottle flies (Lucilia spp.) from muscid lookalikes (Neomyia) in iNaturalist photos. I wrote previously that the distribution of the tomentum (silver reflection caused by microtrichia) would help; below are some further photos to aid in this process.

Male Neomyia

Male Lucilia

Female Neomyia

Female Lucilia 

In each instance, you can see that the tomentum in Lucilia extends much farther dorsally on the frons than in Neomyia.

There was also the tougher question about separating Lucilia cuprina from L. sericata in photos. This is more difficult, because the main character used by the calliphorid expert, Terry Whitworth, is on the back of the head, usually out of sight in photos. There are supporting characters, however, on the dorsum (top) of the thorax. If you look at the humeral callus (“h”, below) and the notopleuron (the triangular area marked “n”), there are a  few tiny setulae along the posterior margins. In L. sericata, there are usually around 6, in L. cuprina 2-3. If you can see that kind of detail in an iNaturalist photo, then you can make a call; otherwise, I suggest leaving them as “Lucilia sp.”

sericata thorax

cuprina thorax

The phorid genus Megaselia Rondani is possibly one of the biggest genera of insects. I say “possibly” because we still don’t know if we should consider all the species currently classified as Megaselia as belonging to a single group. Recently molecular work by Sibylle Häggqvist seems to indicate that most of Megaselia is monophyletic (forms a natural group), but much more work needs to be done.

Just for fun, I made a graph of the described species of phorids, showing the number of species per genus.  This is a representation of how big Megaselia is within the Phoridae. Note that this is the number of DESCRIBED species, and does not take into account all the unknowns. 

For the phorid researchers: does this treemap surprise you? It did me, a little.  I thought Megaselia would be even more dominant. Presumably, once we get to do all the world’s fauna, Megaselia will end up being closer to half of the family.

Or maybe not.

In the recent “City Nature Challenge” (an iNaturalist event co-hosted by our museum, LACM), the question was indirectly asked of me “how do you separate the common greenbottle flies,  classified in the calliphorid genus Lucilia, from the muscid lookalikes in the genus Neomyia that can also be green.” Especially, how would you tell them apart from the photos in iNaturalist, which are often not of stellar quality. My answer is to look them in the face. In both genera, the distribution of tomentum (microscopic extensions of the fly’s cuticle; not ‘hairs’ or setae, which are socketed) is different. The tomentose parts of the frons reflect light as silver or white, so this is often easy to see in photos.

You can see in Lucilia, on the left, that the tomentosity extends much farther up the frons, especially medially (in the middle) than in Neomyia, on the right, which has a dark, tomentosity- free section of the head.

You can see that the attached photo from iNat is a Lucila.