March Flies

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Compiled by Whitney Cranshaw, Colorado State University:

Colorado Insects of Interest

March Flies

Figure 1. March flies.
Figure 2. Bibio albipennis (female), a common species of March fly in the western US. Photograph courtesy Ken Gray Collection/Oregon State University.
Order: Diptera (True Flies)

Family: Bibionidae (March Flies)

Identification and Descriptive Features: Adults are moderate sized (ca 1 cm), dark flies. The sexes can be distinguished by the very large eyes of the male; females possess relatively small eyes and have a head that is more elongated. They are slow fliers. Some species are notably fuzzy.

Larvae are maggot-form with a dark brown head. Colors range from dirty white to brown and on close inspection the body can be seen to be spiny.

Distribution in Colorado: March flies are most abundant in wooded areas and in moist sites. Some have adapted to irrigated lawns and gardens.

Life History and Habits: Despite the name, March fly adults are not seen in early spring. The most common Colorado species (Bibio albipennis, B. atripilosa) are active later in spring, from late April through May. However, other species have peak periods of adult activity in midsummer and several emerge as adults in September and October (Table 1). Where abundant, they may produce noticeable mating swarms. Adults also may visit flowers for nectar, but they are short-lived and survive only a few days.

After mating females deposit masses of eggs in moist soil. Upon egg hatch the larvae feed on decaying organic matter; a few species may also may feed on roots of grasses and other plants producing minor injury. Most often March fly larvae feed gregariously and may be present in a mass of a hundred or more massed larvae. Pupation occurs in the soil and one generation is produced annually.

Table 1.  March fly species known to occur in Colorado.
Species  Period of adult activity
Bibio albipennis Say  late April-early June
Bibio alexanderi James  late April-early May  
Bibio atripilosa James midApril-May
Bibio brunnipes (F.) July-August 
Bibio flukei Hardy August-September
Bibio fluginatus Hardy June
Bibio holtii McAtee August-September
Bibio longipes Loew October-November
Bibio palliatus McAtee  August-September
Bibio rufipes (Zetterstedt)  September
Bibio siebkei Mik midJuly-August
Bibio similis James May
Bibio slossonae Cockerell September-October
Bibio striatipes Walker August
Bibio tristis Williston May
Bibio vestitus Walker June
Bibio xanthopus Weidemann  April-May
Bibiodes aestivus Melander  June
Bibiodes halteralis Coquillet  April-May
Dilophus occipitalis Coquillet July
Dilophus stigmaterus Say July-September
Dilophus tibialis (Loew) June-October
Penthetria heteroptera (Say) late April-early June

The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality.