More then likely the larva of one of the Scarab Beetles, Japanese, June, etc.

Here is a link that might be useful: Scarab Beetle larva

Those guys in your compost are composting fellows.
They don't damage plants.
And they're not Japanese beetles.

In Texas we find humongous rhinoceros beetle larvae in our compost piles, but according to the article they are also found from New York to Florida on the east coast. They only eat dead organic matter and are harmless. It's pretty surprising (but fun) to find them when turning the pile. That could be what you have, however yours are young ones. They take almost a year to mature.

Here is a link that might be useful: Rhinoceros beetle larva

Japanese beetles, rhinoceros beetles, June and May beetles, are all members of the Scarab beetle family along with some 30,000 others. It is often difficult to tell which from the larva since they are very similar. Most all of the Scarab beetle family will lay eggs about August that hatch about September and spend the rest of the year developing until they emerge in May, June, and July as adults to mate and lay eggs to continue the cycle.

Those larvae are destroying my geraniums, they are in pots eating the roots, I have applied recommended insecticides but I can not control them, are very harmful.

Maritza, an easier method of control is to repot those Geraniums into new potting soil.

kimmq is kimmsr

Thanks, kimmq but I have almost 200 plants, I am doing it slowly, when I finish with the last I will have to start with the first