Q. Every fall, I see bot flies terrorizing my horses. I have tried to find a way to get rid of them or to even cut their numbers down, but I have not been successful. I have cows in the next pasture, and someone told me cows attract bot flies. Is this true?

Tracy, Oroville, Calif.

A. Bots are an inevitable aspect of equine ownership, but they are probably more bothersome to you than to your horse.

Bots are the equine representatives of a specialized family of flies (Oestridae) that employs a common strategy of spending the cold winter months within the body of a mammalian host. "Bots" (Gasterophilus spp.) winter in the stomach of horses, and "grubs" or "warbles" live in various tissues or under the skin of cattle (Hypoderma spp.) or rodents (Cuterebra spp.)