Ant movie from the 70's

I would like to find a movie that I remember watching when I was a kid back in the 1970's I think. It was about normal sized man-eating ants. I remember a part about the characters looking through a window and seeing the ants devour a small animal...maybe a bird? I also remember the female character finding her dad or grandfather dead and there was a hole in his hand and ants crawling out of it and something about the two last surviving characters escaping on a horse at the end of the movie I think. That's all I can remember...I know the main character and her dad/grandfather lived on a farm I think. The ants may have been a part of a government experiment or something? I cannot remember for sure.