In the United States we get reports from virtually every state. Anecdotally we hear of higher infestations in warmer areas , but we don't have any hard data to support this.
Insects provoke anxiety in many people.
Some people are absolutely horrified when a moth invades their home or when an ant walks across their picnic table. With some people, just talking about lice is enough to make them scratch and squirm. Some think that they are infested despite intensive examinations that reveal nothing. There appears to be a primal fear associated with insects that relates perhaps to their alienness. We can't say it's because they're not warm-blooded, fuzzy creatures like us, because that doesn't explain why people react so badly to mice.