An adult widow only needs to eat once every couple weeks. If you want, you could feed it twice a week, but it really doesn't need more, and over-feeding will give you a really fat spider, which might look neat, but it makes the spider's abdomen more easy to burst if, say its container were dropped. So I'd recommend once a week. That should be more than enough food to keep it healthy. Also, heavy feeding will prompt the spider ( if it is a wild-caught gravid spider, and wild-caughts usually are ) to produce an eggsac, and that is something you do not want. So once a week should be plenty.