The stable fly is the most concerning pest for producers of both pasture and feedlot cattle, according to Ludek Zurek, Kansas State University professor of entomology. Because stable flies are difficult to control, especially around pastured cattle, he encourages producers to be proactive and begin controlling stable fly populations even when they cannot be seen.

“Stable flies to some degree can actually survive winter here in large piles of manure and spoiled feed around feedlots,” Zurek said. “The maggots dig deeper and deeper into the area that doesn’t freeze. Most of them still die, but we have evidence that some of them make it through the winter and emerge as adults in the spring.”

Ranchers may not be thinking about fly control when temperatures drop, because they can’t see the flies. But, Zurek’s research shows the time to be aware is when ranchers start feeding hay in the winter, especially large round bales.

On pastures, cattle waste some hay when they feed, because it drops from their mouth and then mixes with the manure. When this mixture starts to accumulate in one area, Zurek said, it becomes perfect ground for stable flies in the spring. 

“When feeding these large hay bales, what needs to be done is move the feeders to a new feeding site at least several feet every time, so that the manure and hay do not accumulate in the same place,” Zurek said. “If it accumulates, it retains moisture, and in the spring, stable flies start developing. Then that one site can produce thousands of stable flies.”

In southern parts of the United States, the climate allows for stable flies to live year-round. Many migrate north to Kansas in the early spring, where they find areas with accumulated hay waste and manure from winter feeding. 

Zurek said Kansas typically experiences two peaks for stable fly populations throughout the year. The first and largest peak starts around the end of April and usually lasts until the early weeks of June. Due to the summer heat quickly drying the manure where maggots live, the population will decline during the summer and rebound around the end of August for a second shorter and smaller peak.

The economic effects of stable flies are indirect; while these blood-sucking insects do not transfer any pathogens or parasites to the cattle, the bites are painful. When the pests bite the legs of the cattle, it can be distracting and may cause the herd to bunch for protection. The cattle will even stand in water to escape the annoyance if water is available. All of these reactions lead to a decreased time grazing or eating, which in turn reduces weight gains.

“Unfortunately, in pastures there is nothing that can be done for stable fly control, except controlling the sites where they develop as maggots,” Zurek said. “The ear tags don’t work for stable flies, and insecticides sprayed on the cattle are often brushed off too quickly by the grass.”

Control is easier for feedlots, he said, because they have structures such as buildings, feed bunks and fences that can be sprayed with residual insecticides and will kill the flies when they come in contact with the surface.

Because pastures do not have such structures, Zurek encourages producers to be proactive by taking away the moist manure and hay mixture that creates the flies’ habitat.