Monarch Butterflies

When Will the Fall Monarch Migration Reach You?
The Timing of Fall Migration

Example: When do monarchs begin to roost in the following places?

Answers:
Based on Journey North records from 2002 to the present, roost will be forming in:

  • Ontario: Before August 30th
  • Illinois:
    • Before September 5th (northern Illinois)
    • Before September 19th (southern Illinois)
  • Oklahoma:
    • Before September 19th we can expect the first few to appear, by September 26th there will be more, and more by October 3rd.
  • Texas:
    • By September 19th the first roosts might be present. The number of roosts will climb each week and between October 3rd and 17th the peak number of roosts will form.

Some Notes:

  • The timing of migration is remarkably consistent from one year to the next.
  • If you don't want to miss the migration, begin to watch before the dates that roosts traditionally form, based on the records on this map.
  • Roosts can last from one day to as many as two weeks.
  • Roosts can be large (hundreds or thousands of butterflies) or small (a handful of butterflies).
  • Roosting behavior is assumed to be associated with migration. However, the behavior could begin before migration. It has been seen "pre-migration" in areas with good nectar supplies. Much remains to be learned.

 

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