Diario de bkis

Monarch caterpillars were a familiar sight on the abundant common milkweed at a Barnes Prairie remnant in Racine County, WI for many years. On August 14, 1982, 11 caterpillars were spotted in the field. Seven of these were within an 8 square foot area, and three were on the same common milkweed plant. 1988 was a dry year, with little rain in the summer and many of the common milkweed plants were wilting. On a sunny August 20, 1988 afternoon, we counted 6 caterpillars on common milkweed. Most were near the stems, and two were under the leaves. 1990 was a good year for caterpillars, with 12 found on August 19, 1990, a cool, cloudy day.

In late July 1994, two European mantises were found on vegetation on this Barnes Prairie remnant. Plants, insects, and spiders had been surveyed weekly or biweekly from June through September 1975-1993, and no mantises were recorded in those surveys. However, they may have been present and not seen or recorded during those years.

Plants and flowers that mantises were on in 1994 changed during the summer. On July 21, a mantis was found on black-eyed Susan. In mid-August 1994, wings of butterflies, including monarch, eastern-tailed blue, cabbage white, skippers and red admiral were found under the purple coneflower that a mantis was on.

In early August 1995, Virginia ctenucha and monarch butterfly wings, along with other unidentified wings and insect parts, were found under a common milkweed plant that a European mantis was on.

During a late August 1996 monarch butterfly count, 3 butterflies and 8 caterpillars were seen. A late August 2012 monarch count turned up 2 butterflies and 4 caterpillars. By 2019, monarch butterflies were seldom seen on this prairie remnant. No caterpillars were spotted in June through August, however; a caterpillar was found on the abundant common milkweed in early September 2019. European praying mantises were routinely found in the field that summer, especially on the invasive common buckthorn near flowering plants. A monarch wing, along with unidentified small wings, possibly fly or bee wings, and dragonfly wings, were found under a common buckthorn next to flowering false sunflower in early September 2019.

Beginning in August 2020, European mantises were removed, when found, from the tallgrass prairie remnant. A total of 8 mantises were removed that year. Control of these insects continued through 2023.

Populations of monarch caterpillars found on common milkweed, 2019-2023. Surveys were conducted once weekly, June through September.

Date, No. of Caterpillars seen, Comments

9/7/2019, 1, late instar
8/2020, 1, late instar
9/15/2020, 1, late instar
7/26/2021, 1, early instar
9/1/2021, 1, late instar
8/23/2022, 1, late instar
9/4/2022, 1, late instar
6/20/2023, 1, late instar
8/30/2023, 3, late instar
9/12/2023, 3, late instar

In addition to European mantises, one Chinese mantis was found in 2021, and removed.

Other factors that may have affected monarch butterfly populations during these years have not been considered. However, there has been an increase in monarch caterpillars at this prairie remnant after the European mantises and the Chinese mantis were removed. Future surveys may provide more information.