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3 March 2013, 10 mm long, on a window pane indoors. Wetland habitat in northern Belize, low elevation.

ID help will be appreciated!

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Micropezidae or Neriidae. Tanypezidae also has convergent long veins but would have different antennae.

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Thanks, John! I had wondered about Neriidae (there was a cactus on the other side of the window pane!)

I have been trying to figure out those two black circular areas at the anterior end of the head. Maybe the ocelli are placed there?

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Some genera, e.g. Glyphidops, have shiny spots near the antenna bases.

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Yes, it is Neriidae. Appear to be the genus Glyphidops (99%) or a new genus. The antennal sockets are separated each other, a rare feature among Neotropical genera and species, so my question in relation to genus.

The 'shiny spots' cited by John Carr are the highly modified lunula, and in Neriidae we call them 'antennal sockets' or 'antennal bases'.

And about the popular name 'cactus fly', this name is strongly derived from biology of Odontoloxozus longicornis, a southern Nearctic species, and the best known and studied fly of the family. I'd say about 5% of species may be related to cactus, based on the circumtropical distribution around the world. But if you find any necrotic plant tissues, you can find neriids (like stems of papaya, banana, pumpkin...). They may be attracted by necrotic animal tissues too, but are just venturing there (secondary protein source).