Recently there have been several producers asking about why their cattle are bunching up and standing in groups instead of grazing. Cattle have also been observed standing in water. These behaviors are mainly caused by stable flies.

Stable flies are a primary concern in wet weather and in areas with a mixture of fermenting organic matter, manure, feed grounds, and soil. Feedlots, especially around feed bunks are an optimum environment for stable flies to lay eggs. However, due to the wet weather many areas of Montana have received, stable fly populations have increased, causing cattle to bunch up.

Stable flies are blood feeders and will primarily attack the front legs. The bites can be painful to cattle, and this causes them to bunch up or stand in water to avoid the flies. Stable flies live between 14-24 days and can travel over 10 miles.

When cattle bunch up or spend long periods standing in water, production can be negatively impacted. Based on research completed at the University of Nebraska, average daily gain of cattle can be reduced by 0.44 lbs/head if no treatment is administered. The economic threshold for treatment is 5 stable flies per leg.

One of the challenges for treating adult stable flies is needing to use a spray to control them. Sprays needed to control stable flies need to be applied to the cattle more often than other fly specie control treatments. Make sure to read the insecticide label for treatment method, dosage, and species controlled by treatment. Many methods of control for horn or face flies are not labeled for stable fly control and will not provide control of the specie. If cattle are located in areas with decaying organic material, the ground may also be treated with larvicide labeled for stable flies, which will reduce the development of adult stable flies.

As the weather changes and pastures begin to dry, stable fly numbers may be reduced. However, treatment may need to be considered if the economic threshold has been reached.