My Favorite Flies: Stenomicra

Can flies be cute? Yes, definitely! Take, for instance, Stenomicra angustata:

Stenomicra angustata, from Raleigh, N.C.

For one thing, this guy is tiny – just over one millimeter. It took me a while to find this one in the vial to take a picture. Then there is the nicely contrasting yellow and brown coloration.

I’ve collected this cute little fly only a couple times. The first time was sweeping through rushes and cattails at the edge of a small pond in a suburban park. The one above came from a malaise trap next to a cornfield on the NCSU farm. S. angustata is found across eastern North America, from Texas and Florida to Wisconsin and Quebec, but it is in fact the only Nearctic species of a large, pantropical genus.  There are only about 26 described species, but dozens of undescribed tropical species known in museums.  For instance, anywhere in the tropics, if you look closely at large, broad leaves of Marantaceae or other similar families, you may see something like what I saw in Costa Rica this year:

Stenomicra movie

Notice how the flies walk around the leaf sideways and backwards – but always facing the same way!  This behavior is probably unique to Stenomicra.   The larval biology is unknown for most species of Stenomicra, but specimens in Florida were reared from phytotelmata (water pools formed by plant leaves) in bromeliads (Fish, 1983), a habitat shared with the somewhat related genus Aulacigaster in the neotropics.

A key character diagnosing Stenomicra is the close approximation of the vibrissal setae (two strong bristles just above the mouth, see below); this is more pronounced in the closely related genus Cyamops.  Other diagnostic characters are the forward curving inner vertical bristles (at the top of the head), and the downward bent antennae, with long-plumose aristae (Teskey, 1987).

Head of Stenomicra species, Thailand, showing vibrissal setae.

Head of Stenomicra sp., Thailand, showing vibrissal setae

Taxonomically, the relationship of Stenomicra has been problematic.  It has been placed in several different families, most recently Anthomyzidae, Aulacigastridae, Periscelididae, and even it’s own family, Stenomicridae.  Our recent molecular results (Winkler et al. 2009) suggest it belongs with Aulacigastridae.  One fossil is known, from Dominican amber (Grimaldi & Mathis, 1993).

Finally, for your viewing enjoyment, here’s a few examples of Stenomicra I’ve come across:

Stenomicra spp. from Thailand, Brazil, Costa Rica, and Ecuador

Stenomicra sp., Costa Rica

Stenomicra sp., Australia


Fish, D., 1983. Phytotelmata: Flora and Fauna. In: Frank, J.H., Lounibos, L.P. (Eds.), Phytotelmata: Terrestrial Plants as Hosts for Aquatic Insect Communities. Plexus, Medford, New Jersey, pp. 1–27.

Grimaldi, D.A., Mathis, W.N., 1993. Fossil Periscelididae (Diptera). Proc. Entomol. Soc. Wash. 95, 383–403.

Malloch, J.R. 1927. The species of the genus Stenomicra, Coquillet (Diptera, Acalyptrata). Ann. Mag. Nat. Hist. (9) 20: 23-26, pl. 2.

Papp, L., Merz, B., Földvári, M., 2006. Diptera of Thailand: a summary of the families and genera with references to the species representations. Acta Zool. Acad. Sci. Hung. 52, 97–268.

Sabrosky, C. W. 1965. Asiatic species of the genus Stenomicra (Diptera: Anthomyzidae). Bull. Br. Mus. [Nat. Hist.] Ent. 17: 209-218.

Sabrosky, C. W. 1975. The genus Stenomicra in the Ethiopian Region (Diptera, Aulacigastridae). Ann. Natal Mus. 22: 663-676.

Teskey, H.J. 1987. Aulacigastridae. In J.F. McAlpine et al. (eds.) Manual of Nearctic Diptera, Vol. 2, pp. 891-894. Research Branch, Agriculture Canada Monograph 28.

Winkler, I. S., A. Rung, and S. J. Scheffer. 2009. Hennig’s orphans revisited: Testing morphological hypotheses in the “Opomyzoidea.”  Molecular Phylogenetics and Evolution, 54: 746-762.

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2 Responses to “My Favorite Flies: Stenomicra”

  1. I want to know more about that walking behavior – it certainly is humorous, but what is the adaptive significance?

  2. Isaac Winkler says:

    I don’t know why they walk that way. There are some insects that walk with a certain orientation on vertical surfaces, like the upside-down flies (family Neurochaetidae), which makes more sense, but Stenomicra do this even on a horizontal surface.

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