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CATTLE ECTOPARASITES AND THEIR CONTROL by Alec Gerry, Ph.D., Professor and Cooperative Extension Specialist in Veterinary Entomology, University of California, Riverside to cattle. More importantly, cattle grub eggs deposited Insects, ticks and mites that harm cattle by feeding on blood, skin, tissue, hair or exudates (tears or mucus) at the on cattle legs hatch into fly larvae that burrow into the external body surface of cattle, are commonly described as cattle skin and then migrate through the cattle body until reaching the back of their host. Once at the back, cattle external parasites or “ectoparasites.” Cattle ectoparasites grubs chew an opening in the skin (a “warble”) allowing are often further classified as either permanent, the maggot to get air. Cattle grubs remain in the warble to intermittent or temporary ectoparasites according to the complete their immature life and then they will drop to the degree of association with their animal host. Permanent ground to transform to the adult stage. ectoparasites spend their entire life on a single animal, Temporary ectoparasites include the biting flies such while intermittent ectoparasites spend much of their life as the horn fly, stable fly, face fly, biting midges, black flies, on a single host animal but also spend part of their life horse and deer flies and mosquitoes. Of these pests, the in the surrounding habitat off the host, and temporary most economically damaging in the U.S. are the horn fly, ectoparasites make only brief contact with an animal to stable fly and face fly. Horn flies bite cattle on the back feed on blood or body exudates. during cool weather but move to the belly to feed on Information on the biology and management of sunny days with high temperatures. Horn flies bite many ectoparasites is available through a national extension times each day and remain on the cattle body even when website (Figure 1) managed by veterinary entomologists not biting. throughout North America as part of a USDA multistate In contrast, stable flies bite cattle on the legs and project. lower belly and leave their host after biting to rest in the Permanent ectoparasites include the many different surrounding environment and digest the bloodmeal. Both species of cattle lice and cattle mites. Feeding by lice and horn flies and stable flies acquire blood by tearing through mites can be very irritating to their cattle host, potentially resulting in dermatitis and hair loss. Hide damage can also the skin resulting in painful bites and considerable cow discomfort. occur as cattle rub and scratch against objects in their Face flies feed on eye and nasal excretions, rather environment to relieve the itching caused by lice and mite than blood, and while they do not deliver painful bites, feeding. Lice and mites are typically very host specific they will use their mouthparts to scrape at softer tissues (only live on cattle) and because they lack wings, they around cattle eyes causing irritation to cattle eyes. Face can only disperse to new cattle during direct contact with flies can transmit pathogens to cattle eyes including infested cattle. Therefore, limiting movement of animals infectious bovine keratoconjunctivitis ( “bovine pinkeye”) among herds can help prevent spread of lice and mites. and eyeworms. When fly activity is high, cattle express Intermittent ectoparasites in the U.S. include ticks and cattle grubs. While some ticks will spend their life on a single animal (i.e., the ear tick), most ticks will feed on three different host animals taking one blood meal for each tick life stage (larva, nymph, adult tick). These three-host ticks drop off the host after feeding for several days, and then they remain in the environment until they digest the host blood and transform to the next life stage or lay eggs and die for adult female ticks. Some ticks such as the Foothill Abortion tick (Pajaroello tick) are unusual in that they will feed on many hosts, taking small bloodmeals during each short feeding period. Adult cattle grubs are also called “heel flies” because the adult flies hover near and land on the lower legs of cattle where they lay their eggs. The presence of heel flies can cause cattle to engage © UC RIVERSIDE in a panicked running behavior called “gadding” that can result in injury Cattle on pasture in the Sierra Nevada foothills of California. Image by Alec Gerry. 34 California Cattleman June 2021
