White Grubs, or simply "grubs", are actually the larva form of scarab beetles. While there are thousands of different species, their basic life cycle is the same:
- April: third instar larvae burrow up from below the frost-line where they have been waiting all winter
- May: larvae continue to feed on plant/grass roots
- June: pupate for 1-3 weeks to metamorphize into beetle
- July: emerge as beetle and feed on plant leaves
- August: lay eggs for next season, 30-40 per female
- September: emerge as first instar larvae and feed
- October: molt every 1-3 weeks until full grow larvae (third instar)
- November: burrow below frost line and wait for Spring
These insects are most vulnerable during their first months as a larvae, so spraying during the Fall is highly recommended. I have read several pest control sites that say spraying during the Spring is pointless - the larvae are just too resistant in their mature and/or pupa form.
The picture in this entry is actually taken by me - we found this little guy in one of our potted plants from last year while gardening over the weekend. You can view two larger pictures, where fine hairs can be seen. I am told that entomologists can use the patterns of these hairs to identify the species of beetle.