Lambdina fiscellaria, the mournful thorn or hemlock looper, is a moth of the family Geometridae. It is found in North America, from the Pacific to the Atlantic coast and from Canada south to Pennsylvania, Wisconsin and California.^[1]

The wingspan is about 35 mm. The moth flies from August to early October depending on the location.^[1]

The larvae feed on hemlock, balsam fir, white spruce, oak and other hardwoods.

There are three recognized subspecies:

• Lambdina fiscellaria fiscellaria – eastern hemlock looper
• Lambdina fiscellaria lugubrosa – western hemlock looper
• Lambdina fiscellaria somniaria – western oak looper or Garry oak looper

• 
  Lambdina fiscellaria fiscellaria caterpillar
• 
  Lambdina fiscellaria lugubrosa caterpillar
• 
  Lambdina fiscellaria somniaria adult
• 
  Lambdina fiscellaria somniaria caterpillar

• Anweiler, G. G. (February 8, 2004). "Species Details Lambdina fiscellaria". University of Alberta Museums. E.H. Strickland Entomological Museum. Retrieved November 8, 2020.
• McLeod, Robin (September 1, 2020). "Species Lambdina fiscellaria - Hemlock Looper - Hodges#6888". BugGuide. Retrieved November 7, 2020.