Rotline Question: I found these GIANT two-inch grubs in my compost. My neighbor said they are the Japanese beetle. Should I be concerned?
Don’t worry, be happy, these are compost helpers that have little to no negative impact in your garden. Large grubs like you describe are most likely the larvae of the big iridescent green Figeater beetle, Cotinis mutabilis, a noisy, bumbling aviator. The larvae feed on decaying matter so there is no worry that they will eat your plants. The mature beetle feeds on sweets such as sap, flowers and over-ripe fruit. The larvae can be up to two inches long with rows of bristles on their back. They use the bristles for walking on their backs and are sometimes referred to as ‘Crawly backs’. The fact that they crawl on their backs is supposed to be an identifier, but frankly, I never realized they were traveling on their backside until recently. After all, how do you tell which side is up since they don’t have legs? They are harmless to the garden but can give your hand a little pinch.
The Figeater beetle is frequently confused with the Green June Beetle as well as the Japanese Beetle. The Green June Beetle, Cotinas nitida, is the Figeater’s East Coast Cousin and looks very similar as both an adult and larvae, but can damage the garden. Fortunately, this guy only lives in the Eastern half of the USA. The Japanese beetle, Popillia japonica, is an exotic pest (from you can guess where), that has caused a lot of damage on the east coast. The San Diego County Pest Detection Program places traps for them around the county in the fall as a part of a nationwide monitoring program. Fortunately, these nasty hitchhikers haven’t established themselves in San Diego County. The larvae of The Japanese Beetle can be distinguished from the aforementioned beetles because it possesses a set of legs near the front of the grub.
More information about Figeaters can be found at the UC Pest Management website: http://ipm.ucanr.edu/PMG/r261300511.html