The north of Ireland is currently free from warble fly infestation. However, according to the Department of Agriculture in Northern Ireland, it is important that stock owners remain vigilant and check their cattle regularly.

The warble fly lays its eggs on the forelegs of large animals.

Within a week, the eggs hatch and penetrate the skin. they then migrate throughout the connective tissues or to the esophagus

After a few months, the larvae travel back to the skin surface and cause swellings called "warbles".

They remain under the skin, and when destroyed by pressure, the larvae can cause large purulent swellings. Upon emergence, the fly leaves holes in the skin. Large numbers of such punctures can render cattle hides valueless.

In Northern Ireland, during the period February 1 to August 31, 2016, any sign of warbles must be reported immediately to the local Divisional Veterinary Officer and, if confirmed, treatment of infected animals will be undertaken by Department of Agriculture and Rural Development (DARD) in Northern Ireland at a charge of 75p per animal.

All imported cattle, except those imported from Britain or southern Ireland must be treated with an approved warble fly treatment within 24 hours of arrival in Northern Ireland. The importer must confirm to DARD in writing that such treatment has been carried out.

If the presence of warbles is confirmed by DARD, and the condition had not been previously reported, the herdowner will be required to have the animal treated by a Veterinary Surgeon at his or her own expense, and may also be liable to prosecution.