the way we are [empathetic] to dogs and cats and dolphins and squirrels
  but not to mosquitoes; we happily murder them

There are some philosophies [1] which also care/show empathy towards mosquitoes, and creatures that wouldn't elicit empathy in many people.

Perhaps empathy is, to a certain extent, a learned trait?

[1] http://philosophy.stackexchange.com/questions/7820/are-buddh...