A histomap showing 8 months in the life of an eastern colony of monarch butterflies. Dashed lines indicate the caterpillar phase, and solid lines the butterfly stage, of each generation. Numbers count the generations. When butterfly 5 goes to sleep in Mexico in mid-November, it is the same butterfly, now counted as 0, which awakes in mid-March.
Latitude is indicated on the vertical axis, from 20 degrees North (Mexico City, bottom) to 50 degrees North (Southern Canada, top). Time runs along the horizontal axis to the right, for 8 months, beginning in mid-March.
Details taken from ((Cockrell, 1993), for example, arrival north of 41 deg. in mid-June, average travel speed of 24 km/day, typically 5 generations per season, etc. Also, there is an alternate route below (south of) that shown here, with typically 7 generations of monarchs per season.