Mega-Diverse Megaselia: Flies in the News

by Joseph DeSisto

The phorid fly genus Megaselia contains around 1600 known species, but there are estimates that the genus may contain as many as 30,000 species in total. These flies made the news this year when 30 new species (and 16 already-known species) were discovered in the city limits of Los Angeles (Hartop et al. 2015). This is amazing but not unheard of for Megaselia — an earlier study in Cambridge, England revealed 53 species in a single garden (Disney 2001).

A female Megaselia aurea, scavenging on a dead cricket. Photo by Brian V. Brown and Wendy Porras, used under CC BY 4.0.

A female Megaselia aurea, scavenging on a dead cricket. Photo from Brown and Porras (2015), licensed under CC BY 4.0.

Diversity in Megaselia, however, goes much deeper than a simple species tally. In terms of behavior and ecology, diversity can be awe-inspiring, even within a single species.

Megaselia adults are great, and some of the largest phorid flies around. but the larvae can be just as interesting. Many species are scavengers, and some feed on carrion;  Others are parasites of vertebrates (like bot flies), and still others live inside other insects. Most recently, scientists in Mexico discovered that one species, Megaselia scalaris, is a parasitoid of the tarantula Brachypelma vagans (Machkour-M’Rabet et al. 2015). The tarantula examined contained more than 500 fly larvae which, had the spider not been killed for study, would have ultimately eaten their host alive.

Megaselia scalaris, a fly with incredibly diverse ecological roles. Photo by Charles Schurch Lewallen, licensed under CC BY 3.0.

Megaselia scalaris, a fly with incredibly diverse ecological roles. Photo by Charles Schurch Lewallen, licensed under CC BY 3.0.

Aside from being amazing in itself, this find is significant because M. scalaris already has an incredibly diverse range of lifestyles — the examples here come from a review paper by Disney (2008). In addition to acting as parasitoids on a wide range of arthropods, scalaris larvae have been observed eating decaying plant matter, dung, bacteria and other microorganisms, the leaves and seeds of live plants, already-dead insects, and carrion.

Speaking of carrion, scalaris larvae are well-known for burrowing through up to six feet of soil to feed on human corpses in their coffins. They have also been observed in honey bee hives, scavenging on dead bees, and in amphibian egg masses, feeding on the developing tadpoles. A few specimens were found on the mouthparts of a land crab, where they were apparently eating bits of food the crab’s food.

I could go on … and I will. Sea turtle eggs, shoe polish, a preserved snake specimen recently removed from alcohol, the wounds of living animals from humans to pythons to poison dart frogs, highly toxic millipedes, blue emulsion paint …

Cited:

Brown, B.V. and W. Porras. 2015. Extravagant female sexual display in a Megaselia Rondani species (Diptera: Phoridae). Biodiversity Data Journal 3: e4368. doi: 10.3897/BDJ.3.e4368

Disney, R.H.L. 2001. The scuttle flies (Diptera: Phoridae) of Buckingham Palace Garden. The London Naturalist 80: 245–258.

Disney, R.H.L. 2008. Natural History of the Scuttle Fly, Megaselia scalaris. Annual Review of Entomology 53: 39-60.

Hartop, E.A., B.V. Brown, and R.H.L. Disney. 2015. Opportunity in our ignorance: urban biodiversity study reveals 30 new species and one new Nearctic record for Megaselia (Diptera: Phoridae) in Los Angeles (California, USA). Zootaxa 3941(4): 451-484.

Machjour-M’Rabet, S., A. Dor, and Y. Henaut. 2015. Megaselia scalaris (Diptera: Phoridae): an opportunistic endoparasitoid of the endangered Mexican redrump tarantula, Brachypelma vagans (Araneae: Theraphosidae). Journal of Arachnology 43(1): 115-119.7

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