Face flies, Musca autumnalis, began appearing last month at near treatment levels. In Arkansas, face flies do not reach the abundance to cause economic concerns every year. In general, face flies are more of a concern in the northern half of Arkansas than the south. These flies are economically important as an annoyance to cattle and horses. When face fly abundance is high, grazing may be disrupted, resulting in weight and milk production losses. In addition, they can be vectors of Moraxella bovis, a principal cause of pinkeye, and are implicated in the transmission of the eyeworm (Thelazia sp.) in cattle.
Like several important insects, face flies are an introduced pest, most likely being introduced into Nova Scotia from Europe in the early 1950s and began spreading. By the early to mid-1970s, face flies were common in parts of Arkansas. Although face flies are not a major pest in Arkansas every year, they are major pests in the north and northeastern U.S.
Face flies are found primarily on the face, neck and head of cattle and horses. Unlike the horn flies (Haematobia irritans) that feed on blood, face flies are non-blood feeders similar to house flies (Musca domestica). Instead of blood feeding, they feed using their sponging mouthparts on mucous secretions found around the eyes, nose, mouth and wounds. Nearly all face flies that are found on the animal are female. This is because only females feed on the animal to consume the rich protein secretions necessary for their egg production. Male face flies primarily feed on nectar. It has been estimated that only about 4% of the face fly population is on the animal at any given time. In appearance, face flies are very similar to house flies except about 20% larger. Adult activity begins in early spring and ends in late autumn.
In some ways, the face fly life cycle is like the horn fly lice cycle. One key similarity to the horn fly is that the face fly will only lay eggs in fresh cattle manure. It take about 6 to 12 days for a newly deposited egg to become a fully mature larva (maggot). The fully mature larva transforms into a pupa under the manure pat. Then, from 6 to 11 days later, an adult fly emerges from the pupa. During optimum conditions, it takes from 12 to 23 days for an egg to develop into an adult fly. Unlike horn flies that overwinter as pupae in the soil, face flies overwinter as adults in protected areas such as barns, outbuildings, lofts and attics. During warms spells in winter months, face flies can become household pests as they become active from brief warm-ups.
When an average of ten flies per face occur in the herd, economic loss can occur. When monitoring face flies, count the number of flies on the face of 10 to 15 animals. If the average number per animal begins to approach ten flies per face, treatment is warranted.
Face flies can be difficult to control for three reasons. First, they are primarily found on the animal’s face, which is an area that is often difficult to treat. Second, only a very small percentage of the population is found on the host at any given time. Last, face flies are intermittent feeders, spending very little time on the animal.
With that in mind and when using traditional insecticides, frequent application is often necessary. In the northeastern U.S., dairy producers may install automated face misters/sprayers at the milking barn exit to apply pyrethins and sometimes pyrethroid insecticides to the cow’s face.
Fortunately for us, our populations do not normally reach this extreme abundance. In terms of self-treatment, forced-use back rubbers equipped with fly flips charged with a pyrethroid such as permethrin are effective. A few of the insecticide impregnated ear tags cattle such as Cygard®, Python®, GardStar® plus and a few others can provide control. Because face flies only develop in cattle manure, feed-through larvicides/IGRs (insect growth regulators) such as ClariFly® will prevent new flies from emerging.
Products registered for use against insect pests of cattle are listed in the 2015 Insecticide Recommendations for Arkansas (http://www.uaex.edu/publications/mp-144.aspx).