Occasionally while digging in my lawn, I unearth a greyish green grub that is larger and having a tougher “skin” than a white grub. What insect does it pupate into?
While we are not able to identify the grub from your description, we have been asked a similar question before, “Grey grubs in the lawn“, which contains links to helpful sites, including an Ontario Ministry Agriculture, Food and Rural Affairs site that includes photos of various grubs, as well as life cycles of each insect, which should help you identify what’s in your lawn. A well-written article by Mark Cullen in the Toronto Star, “Cullen: Grubs are shrimp cocktails for skunks” notes that the larvae of June beetles are “grey grubs”, although other references refer to these as “white” grubs. The Cornell University Extension document “Grubs in your lawn?” does not differentiate among grub types, but provides an excellent overview about the grub/beetle life cycle, when to be worried about them, whether you should treat the lawn, etc. Good luck tracking down “your” grub!