Jack Russell Terriers are endlessly energetic, so they need plenty of exercise and love toys that they can run after and fetch. Intelligent and easily bored, they don’t like being left alone for too long, but chewable toys can help stop them becoming destructive at home. Their hunting instincts have been known to lead them astray for days on end, so make sure your garden is secure if they are left outside. Celebrity owner: Mariah Carey.