Decline in populations of Virginia ctenucha moths, Ctenucha virginica, at Barnes Tallgrass Prairie remnants, Racine Co. WI. From 1979 to 2023
Virginia ctenucha, a day-flying tiger moth, was commonly seen at Barnes Prairie remnants from 1978 until 2004. In recent years, their populations appear to be declining. Although there has not been a reduction in acreage of the area surveyed, some of the adjacent farmland has been developed into housing and commercial use, which increased in 2000.
Surveys were conducted biweekly from mid-June through mid-August between 1978 and 2015. Surveys were conducted as described in Comments between 2016 and 2023. The table below shows the Date with the most moths observed on a single day in the summer, from 1978 through 2019. Observations made on multiple days are combined in the Moths Counted column for the years 2020-2023.
Year, Moths Counted, Date, Comments
1978, 15, June 18, Most on common yarrow, also on daisy
fleabane.
1979, 17, June 16, Mid 80s F SW strong wind, partly cloudy.
On common yarrow, fleabane, daisy; count
made in early afternoon.
1984, 19, June 17, On common yarrow and fleabane.
1987, 8, July 19, Hot day, 90s F, flowers wilting.
1990, 12, Mid July, On common yarrow, common milkweed,
thistle, gray-headed coneflower and grasses.
1994, 13, Mid July, On common yarrow, common milkweed,
grasses.
1996, 14, 2nd wk in July, On common yarrow, common milkweed,
ox-eye daisy, grasses.
2000, 9, June 11, Noon, 80 F, on yarrow, thistle.
2004, 11, June 16, Afternoon. 3 on one common yarrow. Other
Nectar plants included daisy fleabane,
thistle, common yarrow. Two were found on
grass leaves. One on teasel leaf.
2008, 3, Mid June, No other information.
2012, 6, June 8, Common yarrow and grass.
2015, 4, August 11, 3 on Queen Anne’s lace, one on thistle.
2016, 3, August 6, No other information available.
2017, 1, August 7, Goldenrod.
2018, 6, June 19, No other information available.
2019, 0, Summer, None seen in late May, June and July,
weekly surveys.
2020, 3, Summer, June 8 (daisy fleabane), June 19 (grass),
July 2 (thistle)
2021, 2, Summer, June 27, one on common teasel leaf. July 8,
no other information available for this date.
2022, 0, Summer, None seen in late May, June and July,
weekly surveys.
2023, 0, Summer, None seen, weekly surveys late May
through August.
Although moth populations have fluctuated between years, there has been a noticeable decline since 2004. Possible causes may be an increase in number of European mantids and/or other predators, earlier mowing of nearby hayfields and meadows, use of pesticides, increase in the number of persons walking in the prairie areas, collecting butterflies and possibly moths, wilting of flowers during dry summers, and/or lower survival rate of overwintering caterpillars due to reduced snow cover. There has been an increase in the use of “bug zappers” in nearby neighborhoods since 2000, but I’m not clear as to whether these moths are attracted to them in early evening or night.
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