Identification, Images, & Information
For Insects, Spiders & Their Kin
For the United States & Canada

Family Bibionidae - March Flies

Unknown - Bibio articulatus - female Bibiodes - Bibiodes halteralis - female Bibio - Bibio articulatus - male fly060520-17 - Dilophus spinipes - male Penthetria heteroptera - male Penthetria heteroptera? - Penthetria heteroptera - male Bug - Bibio femoratus - female Bibio - female
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
Synonyms and other taxonomic changes
Revision in(1)
Explanation of Names
Bibionidae Fleming 1821
Called lovebugs because the adults spend an inordinate amount of their short lives mating and copulating.(2)
ca. 60 spp. in 6 genera in our area(3), >1,100 spp. in 12 genera total(4)
5-12 mm
Small to medium-sized flies with robust bodies, usually dark, often with brightly colored thorax. Characteristics [cite:185010] (reference deleted?):
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. (adults) in(5)
worldwide; most diverse in the Neotropical and Palaearctic regions, but distribution patterns vary considerably between genera(3)
larvae live gregariously in the top layers of soil and leaf litter, rotten wood, and dung; adults often found on flowers(3)
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(3).
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)(3)
Larvae don't wander too far from their birthplace and form family gatherings underground.(2)
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(3)
Internet References
Fact sheet (Denmark et al. 1998-2012)[cite:185010]
Works Cited
1.Revision of Nearctic Bibionidae including Neotropical Plecia and Penthetria (Diptera)
Hardy D.E. 1945. University of Kansas Science Bulletin 30(15): 367-555.
2.Hidden Company that Trees Keep: Life from Treetops to Root Tips
James B. Nardi. 2023. Princeton University Press.
3.Evolution and classification of Bibionidae (Diptera: Bibionomorpha)
Fitzgerald S.J. 2005. Ph.D. Thesis, Oregon State U. 385 pp.
4.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.
5.The Bibionidae of California
Hardy D.E. 1961. Bull. Calif. Insect Survey 6(7): 179-195.