Painted Lady Invasion?

[Paul Cherubini]

Stanley Selkow wrote:
 
>       Allow me to pose as a mathematics guru:
>      "All it takes is one or two aliens to establish a new
>       population"

But Painted Ladies have been recorded in Barbados for years.

> "or alter a genetically similar but locally adapted existing population"
> "or introduce a new pest or parasite."

My question was not about genetics or pathology, but about the density
of Painted Ladies required per square mile before a casual or
experienced observer would have a realistic chance of noticing them on
any given day. If you can explain the dispersal math to us, we would be
grateful.

Paul Cherubini, El Dorado, California