INTRODUCTION.
The common name of face fly comes from the adult habit of feeding on the mucus and watery
secretions found around the eyes, nostrils, and mouths of cattle. They are a nuisance pest
in structures where their behavior resembles that of cluster flies, coming in to
overwinter and being active on warm winter days. In the early 1950's, face flies were
introduced from the Old World and are now found throughout most of the United States and
Canada.
RECOGNITION.
Adults about 1/4" (6.5-7 mm) long, about house fly size or slightly larger. Color
dull gray; head with parafrontals (sides of front next to eye) bright gray, wide, nearly
as wide as median frontal strips; thorax with 4 narrow black longitudinal stripes on
dorsum; no pale spot behind head or on soutellum (rear tip of thorax); abdomen with dorsum
entirely black in ground color, with gray and black pattern. Mouthparts sponging. Female
with eyes much more widely separated than on male, male's almost touching. Wing with 4th
(3rd long) vain (M) sharply bent forward near tip, towards and almost meeting 3rd vein at
wing margin; with strong tuft of bristles at base of calypter (flat basal lobe; best seen
by lifting upper calypter/lobe).
Mature larva about 1/4-7/16" (7-11 mm) long; eyeless, legless, and
tapering towards head from large rounded rear segment, head represented by 1 pair of dark
hooks. Color yellowish. Posterior spiracies (breathing pores) with spiracular area smooth
and dark, 2 plates each with spiracular openings sinuous/winding slits which may/may not
be surrounded by a thin black ridge (peritreme), button (round eedysial/molting scar) away
from margin towards center, not attached to peritreme/margin.
SIMILAR GROUPS.
House fly (Musca domestics) with wing calypter (basal lobe) lacking
bristle tuft, male with eyes well separated, female head with parafrontals (sides of
front) each about 1/3 width of median frontal stripe.
Flesh flies (Sarcophagidae) have only 3 dark longitudinal stripes on
thorax, tip of abdomen usually red/pink.
Stable (Stomoxys calcitrans) and false stable (Muscina stabutans)
flies have wing with 4th (3rd long) vein (M) curved towards 3rd vein but not sharply
angled; in addition stable flies have piercing mouthparts and thorax with pals spot behind
head while false stable flies have sponging mouthparts but a pale scutellum (rear tip of
thorax).
Little house (Fannia canicularis) and latrine (F scalaris) flies have
wing with 4th (3rd long) vein (M) straight.
Cluster fly (Pollania rudis) with golden hairs on thorax, thorax
lacks 4 dark longitudinal stripes.
BIOLOGY.
Females lay their eggs (30-230) only in fresh (less than 1 day old), undisturbed cow
droppings/manure. The eggs are deposited just below the surface and have a black
respiratory stalk on one end. Eggs hatch in 10-23 hours. The 3 larval instars require
about 3-4 days. Last instar larvae migrate from inches to 30 ft (9.1 m) from the dropping
to pupate in the soil. The pupal stage lasts about IO days. Developmental time (egg to
adult) outdoors requires about 17-18 days at 77-86'F/25-30'0. Non- overwintering adults
live up to 55 days.
HABITS.
Face flies are present outside from April to October, with numbers building up towards
autumn. When the temperature is about 60'F/16'C, large numbers of primarily female flies
cluster around the faces of cattle and horses where they feed on the mucus and watery
secretions around the eyes, nostrils, and mouth. They also feed on the blood coming from
wounds made by biting flies and on dung fluids. Males feed primarily on flower nectar.
During the day, adults can also be found frequenting bushes, tall pasture grasses and
weeds, fence posts, and rocks, in addition to the animals. In dispersal studies, marked
flies were recovered up to 0.9 miles (1,500 m) away 46 hours after release; they are known
to travel up to 1 1 3 miles (70 km).
Females lay their eggs only in fresh dung, preferably less than I hour old. The dung
must be undisturbed which means breeding sites are in pastures and on range land.
Adults seek sheltered locations in which to overwinter beginning in late August or
September. Such places include attics, wall voids, and basements of structures especially
on the south and west sides of the structure. They tend to use the same structure year
after year.
They can be a problem or nuisance in the autumn, winter, and/or spring; autumn when
they enter to hibernate; on warm, sunny winter days; and again in the spring when they
attempt to leave the structure. They can be stimulated by warmth to resume activity almost
any time. Sometimes it takes no more than the furnace to be turned on and thoroughly warm
the inside of the structure to start activity, but it usually additionally requires a
bright sunny day to warm the walls from the outside. Once stimulated, face flies seek
light. This is why they usually come out around loose-fitting wall switches and outlets,
ceiling fixtures, window and door frames, window pulleys, etc. Face flies can usually be
found at windows crawling on the panes or frames, or around lamps or lights.
