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Family Bibionidae - March Flies

Mystery Fly - Bibio - male Black Colored Fly - Penthetria heteroptera - female Love Bug - Plecia nearctica - female March Fly - Bibio - female March Flies Mating - Bibio - male - female What Are These Thing? Dipteran - Bibio - female Black Fly - Dilophus - male
Classification
Kingdom Animalia (Animals)
Phylum Arthropoda (Arthropods)
Subphylum Hexapoda (Hexapods)
Class Insecta (Insects)
Order Diptera (Flies)
No Taxon ("Nematocera" (Non-Brachycera))
Infraorder Bibionomorpha (Gnats, Gall Midges, and March Flies)
Family Bibionidae (March Flies)
Other Common Names
Lovebugs (Plecia), St Mark’s Flies (esp. Bibio), Fever Flies (esp. Dilophus), Garden Flies
Numbers
ca. 60 spp. in 6 genera in our area(1), >750 spp. in 9 genera worldwide(2)
Size
5-12 mm
Identification
Small to medium-sized flies with robust bodies, usually dark, often with brightly colored thorax. Characteristics (Univ. Florida--ENY 3005):
body usually black covered with long hair, thorax red or yellow in some genera, such as Plecia
antennae short, placed low on face
ocelli (simple eyes) present
males with large compound eyes, divided into upper and lower sections
tibiae with prominent apical spurs
pulvilli (pads) present beneath tarsal claws.
wings clear or dark, some have dark spot on the anterior margin
anal angle of wing usually well developed
Some of these characteristics shown on image(s) below:

Genera can be distinguished by wing veins:
Rs forked, R2+3 at sharp angle, R4+5 nearly straight (Southeast): Plecia
Rs forked, R2+3 at sharp angle, R4+5 distinctly curved (North): Hesperinus brevifrons
Rs forked, R2+3 parallel to wing: Penthetria heteroptera
Rs unforked, partially merged with M: Bibioides
Rs unforked, basal section of Rs much shorter than R-M crossvein: Dilophus
Rs unforked, R-M crossvein shorter than or similar in length to basal section of Rs: Bibio
The last two also have strong protibial spurs.
Key to CA spp. (adulta) in(3)
Range
worldwide; most diverse in the Neotropical and Palaearctic regions, but distribution patterns vary considerably between genera(1)
Habitat
larvae live gregariously in the top layers of soil and leaf litter, rotten wood, and dung; adults often found on flowers(1)
Food
larvae feed on leaf and needle litter, decaying organic matter, also on subterranean structures of live plants; Hesperinus larvae are xylophagous and bore in the decaying wood of various deciduous trees; adults apparently feed on nectar or pollen, but also on honeydew and plant liquids associated with damage from other insect feeding(1); adult Plecia do not feed.
Life Cycle
Adults emerge synchronously in huge numbers and often form dense mating aggregations. Males form loose "swarms" and copulate immediately with females as they emerge from the soil. After mating, female bibionines dig a small chamber in the soil with their fossorial fore tibiae, lay eggs, and die within the chamber (Plecia lay eggs on the soil surface). Adults are short-lived (3-7 days)(1)
Remarks
larvae may damage cereal crops, vegetable crops, ornamental plants, nursery stock, grass, and forage crops; adult Bibio and Dilophus may be important pollinators in orchards and are the exclusive pollinators of some species of Orchidaceae and Iridaceae(1)
Print References
D. Elmo Hardy (1945), "Revision of Nearctic Bibionidae Including Neotropical Plecia and Penthetria (Diptera)", University of Kansas Science Bulletin, Vol. 30, No. 15. (Full Text)
Works Cited
1.Evolution and classification of Bibionidae (Diptera: Bibionomorpha)
S.J. Fitzgerald. 2005. Ph.D. Thesis, Oregon State University. 385 pp.
2.USDA Diptera Site (now closed)
3.The Bibionidae of California
D.E. Hardy. 1961. Bull. Calif. Insect Survey 6(7): 179-195.