General comments:
Widespread but local across both counties. The wider availability of pheromone lures has led to a big increase in records of adult males in the past few years. There has probably not been any change of status. Although female Emperors sometimes come to light traps, this is a rare event, whilst the large and striking caterpillars are surprisingly well camouflaged and are extremely difficult to find, especially when feeding in difficult to search bramble patches.

Hertfordshire Notes:
Evidently widespread, but there are some areas where searching for it has failed.

Middlesex Notes:
Widespread, but probably more localised than in Hertfordshire.

Recorded in 31 (76%) of 41 10k Squares.
First Recorded in 1887.
Last Recorded in 2024.