The weasel is the smallest member of the mustelids (ferrets, stoats, otters) and the world's smallest carnivore. It was introduced into New Zealand in 1885, to help reduce rabbit numbers, along with ferrets and stoats, but, although released in greater numbers, did not thrive.
The government changed its release policy in 1903 but it was too late. It was not until 1936 that legal protection was removed.
Weasels are found worldwide except for Antarctica and Australia. They inhabit a wide range of environments, from pastoral land and scrub to exotic forest and bush margins. They are great predators of mice but also prey on native birds, eggs, lizards, insects and frogs. They are efficient hunters, and will kill even when their belly is full.
Their slender shape and short legs allow them, uniquely, to enter the burrows of prey where they corner their victim, wrap themselves around the prey to immobilise it and then bite the back of the neck to kill. They then take over the burrow, lining it with fur and leaves to make it a den.
They hunt both day and night, mainly on the ground, but can climb. Hunts can cover 2.5km at speeds of up to 25km/h. Prey can include animals much larger than themselves, and surplus can be carried back to the den and cached for later use. Their body shape, size and metabolism mean they have a very high energy demand and need to eat one-third of their body weight in food each day.
They are known to 'hypnotise' their prey by dancing, but it is now thought this behaviour may be due to the discomfort of internal parasites.
Weasels have a deep brown-light brown body and a short brown tail. The belly is white with an irregular line where it meets the brown. Males are larger than females (150gm vs 80gm), and are 20-35cm long.
Territory size depends on food availability but can be 4-8ha. Females tend to stay within their own territory but males will roam further, especially during the breeding season. Being related to the skunk, they use scent marking, and will squirt anal sac secretions when scared.
Females have 4-6 kits per litter and can have two litters a year. Gestation is five weeks, with the kits weaned at 4-5 weeks. They are good hunters by eight weeks. Adults are solitary except at mating. Wild weasels can live up to three years but males rarely do, as their roaming makes them more susceptible to predation.
Control of weasels is generally by trapping. DoC 200 stoat traps baited with rabbit work well, and the newer Good Nature traps can be baited for mustelids too.
The collective nouns for weasels include boogle, gang, pack and confusion.