Overwinters as an egg and adults come readily to light.
Note August and September Thorns cannot be separated on flight period; they both come out in July. There is no kink in the outer cross-line where it meets the wing and it generally holds its wings at a steeper angle.
Recorded in 93 (66%) of 140 10k Squares. First Recorded in 1867. Last Recorded in 2019. (Data up to end 2019) Additional Stats