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