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Monarch Degree Days for the Last Three Seasons

By Janis Lentz and Chip Taylor

To get a better idea of how this season compares with the two previous seasons, we’ve calculated the degree days for each year for five cities: Winnipeg (Manitoba, Canada), St. Paul, MN; Des Moines, IA; Lawrence, KS; and Dallas, TX. The calculations start with the approximate date of first arrival of monarchs for each location. The accumulated degree days as of 23 August are shown in Table 1.

Table 1. Accumulated monarch degree days and potential monarch generations for selected cities as of 23 August for the last three years. The number of degree days for each year is listed in the year column. Gens = the potential number of generations

A comparison of the accumulated degree days for each of the last three years for the cities listed shows that 2005 has been warmer than either 2003 or 2004, except for 2003 in Winnipeg. The result is a higher number of potential monarchs generations this year. The greater potential for reproduction due to higher temperatures could explain the many reports of favorable monarch numbers this summer.

In the tables below, the monarch degree days are shown for Winnipeg, St. Paul, Des Moines, Lawrence, and Dallas for the past three seasons from 15 July through 23 August. For the complete degree day data, from the average date of first arrival of monarchs for each of these cities, please see the July Update. We will add to the tables below through the September Update.

Winnipeg, Manitoba (Canada) 49:54:00N 97:07:48W

St. Paul, MN 44:56:52N 93:06:13W

Des Moines, IA 41:34:36N 93:37:03W

Lawence, KS 38:57:46N 95:15:19W

Dallas, TX 32:47:39N 96:45:55W