Harvest mice are Britain's tiniest rodent. They're not considered pests themselves, and in fact are actually seen as pest control; they prey on agricultural pests, saving farmers on pesticides. They also take their place in the food chain, supporting predators like hawks and owls, which supports overall biodiversity.

The mice's habitats are increasingly being infringed upon by human development. In order to provide them a safe place to live, British conservation consortium The Wildlife Trusts provides readymade nests for them—by cutting holes in tennis balls donated by Wimbledon:

The balls are attached to poles that are placed in field. The mice, talented climbers, readily populate them.

Wimbledon goes through some 55,000 tennis balls with each competition, so unlike Britain's human denizens, the harvest mice will suffer no housing crisis.