No voles in several days.
The morning after I set out snap traps, I went out to investigate. The trap in hoop house #2 had gone missing. Wow!
John and Mom share the opinion that the Red Fox who lives in the meadow took it. Now I ask you-how plausible is this? To execute said theft, Mister Fox would have jumped the fence topped with barbed wire, gotten into the hoop house and under the row cover without disturbing anything and then taken the cheese (with trap attached) and retreated for his meal.
Anyway, this fox has been seen in close proximity to the back fence when dogs are elsewhere. My theory is that the voles are after the greens and the fox is after the voles. As to what happened to the snap trap? I really don't know.