Does this attract horse flies?

It depends on the type of fly you are referring to as a Horse Fly. This trap is proven to catch False Stable Flies, Face Flies, Flesh Flies and many others, but it's not proven for flies that bite. It is known as a "vacuum cleaner" for flies and really does the job well for nuisance and disease-carrying flies. For biting flies, we recommend other products in the RESCUE! line: TrapStik for Biting Flies, Mosquito DecoShield or Mosquito GoClip. Although the last two are labeled for mosquito, they work on any insects seeking flesh to bite. Hope this helps!