While I find this interesting I have a question that although does not relate to humans' fear of rats does refer to their association with the Black Death. My history books claim that it was the black rat that spread the bubonic plague, but my home encyclopedias say it was the brown rat. Wikipedia goes on to say that it was the black rat that spread the disease with its fleas, but was reduced when the larger brown rat drove most black rat populations out of urban areas - taking the fleas with them. Which is true? And why can't the rat fleas infect both if they can also infect squirrels regardless of the specific rodent species?