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Family Empididae - Dance Flies

Rhamphomyia - female Mosquito Hairy Star Tulip - Empis Empis sp. - Empis - male Bee Fly(?) Second Glady Fork fly - Rhamphomyia - male Pennsylvania Fly for ID - Hilara seriata - male Long-tailed Dance Fly (Rhamphomyia longicauda) ? - Rhamphomyia - female Diptera. Therevidae - Empis - male
Classification
Kingdom Animalia (Animals)
Phylum Arthropoda (Arthropods)
Subphylum Hexapoda (Hexapods)
Class Insecta (Insects)
Order Diptera (Flies)
No Taxon (Orthorrhapha)
Superfamily Empidoidea
Family Empididae (Dance Flies)
Other Common Names
Balloon Flies, Empids, Dagger Flies
Synonyms and other taxonomic changes
used to be treated in a broad sense to include all the Empidoidea except Dolichopodidae(1)(2)(3); here treated as defined in(4)(5), with the subfamilies Hybotinae, Ocydromiinae, and Tachydromiinae treated in Hybotidae; Brachystomatinae, in Brachystomatidae
=Empidae
Explanation of Names
Empididae Latreille 1804
see Empis
Numbers
~460 spp. in >30 genera of 3 subfamilies in our area(3), >3,140 spp. in >100 genera total(6)
Identification
Small to medium sized flies, usually elongated and mostly dark colored. They have a rounded head and a distinct neck, a large and humpbacked thorax and long tapered abdomen. The legs are slender and sometimes the front legs are raptorial, for grasping other insects. The proboscis is often long and pointed.(5)
First antennal segment bristled and often longer than in Hybotidae and similar families. If no veins forked, prosternum may also be large and fused with epimera.
Range
Worldwide
Food
small insects, and occasionally nectar; larvae often feed on decaying organic matter in the soil, some are predatory
Life Cycle
Larvae found in a variety of situations--aquatic, semiaquatic, in dung, in bird nests, among roots and fungi(3)
Remarks
In mating swarms, males fly up and down in a sort of dance. Often they have captured an insect, wrapped it in silk, and hold it as an offering for females. Females seem to choose the male with the most enticing offering. Sometimes a male may offer just an empty ball of silk.

    ← Males with "nuptial gift balloons" →

Comments on swarming from Paul Beuk:
You may have male swarms, female swarms and mixed swarms. In the case of the first two it may be that the other sex does not form swarms but joins the existing swarm for mate selection, or there are nearby separate swarms and specimens from one of those leave for the other to select a mate.
Different species swarm at different times of day. Some may swarm during the whole day, others maybe only for an hour at dusk, etc.
The location of the swarm is determined by markers. These may be very specific (under a overhanging branch in the sun, so the swarms may move with the sun) or rather 'generally defined' (along a slope, creating a very 'long' swarm, or over the water surface of a brook).
Nuptial gifts are not known for all mating dance flies. They are mostly found in the subfamily Empidinae (in genera like Empis, Rhamphomyia and Hilara...the latter including the balloon flies).
Print References
Cumming, J.M. 1994. Sexual selection and the evolution of dance fly mating systems (Diptera: Empididae; Empidinae). The Canadian Entomologist 126: 907–920. (Full Text)
Works Cited
1.Insects: Their Natural History And Diversity: With a Photographic Guide to Insects of Eastern North America
Stephen A. Marshall. 2006. Firefly Books Ltd.
2.Manual of Nearctic Diptera Volume 1
Varies for each chapter; edited by J.F. McAlpine, B.V. Petersen, G.E. Shewell, H.J. Teskey, J.R. Vockeroth, D.M. Wood. 1981. Research Branch Agriculture Canada.
3.American Insects: A Handbook of the Insects of America North of Mexico
Ross H. Arnett. 2000. CRC Press.
4.The morphology, higher level phylogeny and classification of the Empidoidea (Diptera)
Sinclair, B.J. & Cumming, J.M. 2006. Zootaxa, Vol. 1180 (Magnolia Press, Auckland, New Zealand).
5.Cumming J.M., Brooks S.E. (2006) Homepage for Empidoidea resources
6.Order Diptera Linnaeus, 1758. In: Zhang Z.-Q. (ed.) Animal biodiversity: An outline of higher-level classification...
Pape T., Blagoderov V., Mostovski M.B. 2011. Zootaxa 3148: 222–229.