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We have been told over the years that the last of the monarchs that overwinter in Mexico arrive at the colony sites during the first week of December. This may in fact be the case. However, as I sat down to write this we received a call from Kentucky with a report of a sighting today. Last week there were a least 5 reports of late monarchs and there was one report from the Dallas area of large numbers of monarch larvae being found on milkweeds in butterfly gardens.
The exceptional number of late sightings appears to be due to the northern position of the jet stream which has resulted in an unusually warm fall for most of the central and eastern United States. The first two weeks in November were the warmest ever recorded for eastern Kansas. We are not certain whether any of these late monarchs are still migratory or have any chance of reaching the overwintering sites in Mexico. These observations seem to indicate that there may be a number of late monarchs each year which are usually killed as the jet stream dips southward east of the Rockies in October.