Should C++ 'interfaces' have a virtual destructor

Possible Duplicate:
Destructors for C++ Interface-like classes

Consider a simple example of a C++ abstract class, used to model an interface:

class IAnimal
{
  virtual void walk()=0;
  virtual ~IAnimal(){}
};

Is it better to have the destructor, or not? I don't think the destructor can be pure virtual, at least my tests give linker errors, so should an empty destructor be included?

EDIT: sorry, typo. It's a destructor not a constructor.