If you wife "might have been bitten" by the spider, that does not matter; unless (1) she was bitten and (2) suffered some relatively significant injury or medical costs, there is no point in thinking about legal action. In a lawsuit, you can only recover an amount commensurate with the extent of your injuries or costs; if there are no injuries or costs, you cannot recover any compensation, which makes a lawsuit pointless. (Or worse than pointless--you'd spend money it, then receive nothing for your expense.) There is no compensation owed for "might haves."Even if she had been bitten or injured, to recover money in a lawsuit, you'd to be able to prove fault--i.e. that the spider was in the lettuce when purchased. If the spider, for example, got into the lettuce while your wife was cleaning it in your kitchen, there would be no fault and no recovery. Proving where the spider came from could be difficult.