March Fly
Bibio marci · Insect, Invertebrate, Cold-blooded, Wild
Animal Family
Family Bibionidae, Order Diptera, Class Insecta
Animal Category
Insect/Arthropod
Breed / Variety
St. Mark's Fly
Conservation Status
Least Concern with a stable population trend; common and widespread across its range.
About This Creature
Small black fly with characteristic long dangling legs and transparent wings. Adults typically measure about 9 to 15 mm in length. Males have noticeably larger eyes that meet at the top of the head, while females have smaller, widely separated eyes and an orange-red thorax or legs depending on the exact morph, though Bibio marci is predominantly black with dark wings.
Physical Characteristics
Segmented body divided into head, thorax, and abdomen; robust black body covered in fine hairs; clear membranous wings with distinct dark venation and a dark stigma; long, spiny legs that dangle during flight; short antennae composed of multiple segments.
Behavior & Temperament
Socially active in swarms during spring, particularly around St. Mark's Day (April 25th); diurnal activity; adults do not bite and are clumsy flyers; feed primarily on nectar; larvae live underground and feed on decaying organic matter and plant roots.
Habitat & Diet
Origin Region
Europe and parts of Asia, commonly found in temperate regions
Habitat
Grassland/Savanna, Wetland/Marsh, Agricultural; Terrestrial and Aerial
Diet & Nutrition
Adults are nectarivores feeding on flower nectar and pollen; larvae are detritivores feeding on decaying plant material, humus, and occasionally living roots.
Lifespan & Health
Adult stage is very short-lived, lasting only about one to two weeks in spring; the majority of their life cycle is spent underground as a larva lasting up to a year; preyed upon by birds, spiders, and insectivorous mammals.
Special Characteristics
Known for synchronized mass emergences in spring; larvae contribute significantly to soil aeration and organic matter decomposition.
Ecological Information
Primary decomposers in the larval stage, recycling nutrients in the soil; adults serve as pollinators for various flowering plants and provide an important food source for insectivorous birds and small predators.