we found a cacoon underground, what could it be?

Question

the other day my son was digging up some rose bushes by our house, he found a cacoon about 2-3 inches down in the dirt. it's dark brown, about 3-4 inches long, as thick around as a plumper hotdog. if you look closely you can see a wing-like structure, so it will be some kind of butterfly or moth, but we'd like to know if anyone can help us identify the type. we've never known of any that burrow to morph. it's way too big to be a cycada. thanks for your help!

Answer 1

Several types of moths pupate underground, for example, the Death's Head Hawkmoth:
http://en.wikipedia.org/wiki/Death's-head_Hawkmoth#Pupa

Also, many of the other Sphinx Moths do as well:
https://ag.arizona.edu/yavapai/anr/hort/byg/archive/sphinxmoths.html

Answer 2

coleopteras (beetles and related animals) lay the eggs underground. the larvae eats plant roots, causing more than just a little scratch to the plant if the larvae exist in huge number. they might kill the plant, be careful with your rose :D