. >> reporter: this english manor in the woods near boston is denny and win swenson's dream house.n they moved here ten years ago, they were thrilled to see a lot of deer. >> and it was so exciting because they're such beautiful animals. they seemed harmless. wow, we felt like we had arrived. >> reporter: but today she is a more than a little wary of the deer. in fact, she believes controlling their numbers is the only practical way to stem the spread of lyme disease. humans are infected with lyme from tick bites, and ticks like to feed on deer. >> there's a trail there that the deer love. >> reporter: this is deer country here? >> yeah, yeah. we have tons of deer. >> reporter: the state says that there are about 85 deer per square mile in the adjacent 7,000 acre blue hills reservation. ten per square mile is considered a density that could reduce the spread of lyme. deer were hunted nearly to extinction a century ago in the u.s. today, thanks to legal protection and regulated harvests, the deer herd nationwide has exploded to more than 30 million. this creates a host of problems,