A mask to protect a horse from insects is attachable to the horse's bridle. The mask has a cover member, such as flexible plastic screen material, that extends between the brow band, the nose band and the cheek pieces of the horse's bridle. The mask is removably attachable to the bridle, such as by loop and hook fastener. When attached to the bridle, the edges of the mask can be positioned either above or underneath the corresponding part of the bridle. A snug fit between the mask and the corresponding part of the bridle prevents insects from getting under the mask. Two darts space the mask away from horse's eyes. Elastic portions of the mask allow a snug fit between the mask and bridle while the invention is being worn.