What is it? Is it good or bad? I dumped the compost onto my newest bed and about 8 of these guys fell out
The Mockingbirds went nuts, swooped down and gobbled them up.

Are they a sign of trouble in my composted?

It looks like a "white grub", the larva of a Scarab beetle. One would need to examine some hairs on its posterior end to determine which it is. I guess from a compost point of view it means the heap isn't getting very hot?

Indeed, the pile is not hot, other then being baked in the Southern California sun. I believe this composted is too small to really cool the pile.

Are they OK in the garden or will it eat my young plants?

They are okay in the garden...they eat decaying matter. If a root or two is in the way of their foraging, they will cut through. But they don't go after living tissue.

BlondieRides said:

Are they OK in the garden or will it eat my young plants?

Some Scarab beetle larvae do eat plants, others do not. Scarab beetles or their larvae that eat plants include the Japanese beetle, the June beetle and others - they are the grubs that get into lawns to eat the grass roots and cause skunks etc. dig them up for lunch. Japanese beetle adults also eat above ground parts of plants but I don't think JBs are established in California? Anyway, since these grubs are in your compost pile chances are they quite likely are not a kind that eats plants.

If it's a large grub, we call them Rhinoceros grubs/beetles. They don't harm anything that I know of. They used to scare me when I'd find one in the garden!

Like I said, they (grubs) eat decaying matter. Adult beetles are another thing entirely...certain ones could wreak havoc on plants and crops. Might be worth taking a grub to your local agri extension office to find out more and whether to be concerned about this particular critter.

Rhinoceros beetles were found on our island in about 2007. Since then they are slowly taking over the island decimating our coconut trees and now betel nut trees. The government has been trying all kinds of means to stop them...so far no success.

"Adults take a variety of foods, many feeding on fungus, dung, carrion, or other decomposing matter, some on sap, pollen/nectar, fruit, foliage; a few are agricultural pests, others, important pollinators. Larvae typically feed on decomposing matter: dung, carrion, etc., or live in soil and feed on roots "

This is from the Bugguide page on Scarab beetles:
http://bugguide.net/node/view/...

It depends on the species whether the larvae feed on plant roots or not.

I agree about the extension office if you are concerned. This might help:
http://ucanr.edu/County_Office...