Allee effects can play a critical role in slowing or preventing the establishment of low density founder populations of nonindigenous species. Similarly, the spread of established invaders into new habitats is influenced by the degree to which small founder populations ahead of the invasion front are suppressed through Allee effects. We used empirical data on the gypsy moth, an exotic invader in North America, to quantify the Allee threshold across geographic regions and report that its strength is subject to spatial and temporal variability. Moreover, we present what is to our knowledge the first empirical evidence that geographic regions with higher Allee thresholds are associated with slower speeds of invasion.