Thistle Caterpillar

Thistle Caterpillar

Description:

  • Vanessa cardui, also known as the ‘Painted Lady Butterfly’ as an adult
  • Adults are orange, brown and black and measure 2-2.8” long at the wings, ~ 1” long body
  • Eggs are pale green with 14-19 vertical ribs
  • Caterpillars are creamy white to gray brown with distinctive branching spines and often a yellow stripe, 1.5 to 1.75” long
  • Chrysalids can be metallic green, brown or blue – very striking in the field

Life Cycle:

  • Butterflies arrive from Southern U.S. & Mexico in mid June
  • Adults lay eggs which develop in ~7 days
  • Caterpillars hatch out and feed for 2-6 weeks then pupate in 7-17days
  • Butterflies emerge and finally migrate South in September
  • Thought to be 2 generations per year
  • Not known to overwinter in the Midwest

Economic Injury:

  • Thistle Caterpillar feed on over 300 plants as larvae, soybean defoliation is the main concern
  • Field edges tend to be the hardest hit and are great places to begin scouting
  • Treatment is warranted at 30% defoliation during the vegetative stages and 15-20% during the reproductive stages