Gegeines

Gegeines is the Greek name for the Earthborn. They have six arms each and wear nothing but leather loincloths.

History
Upon landing on an island near Bear Mountain, Jason and the Argonauts encounter the Gegeines who raided their ship when the others went into the forest to find supplies. Heracles was among the Argonauts guarding the ship at the time and managed to slay some of them until Jason returned. Once some of the other Gegeines were killed, the Argonauts set sail.

The Lost Hero
They look like clay statues of giants that have six arms. They are 7-8-ft tall. They have superhuman strength, and can generate large surprisingly sharp rocks in their hands. They are the servants of the Giants and born from the Earth as shock-troops for the Giants during the Original Giant War. Once Jason, Piper McLean, and Leo Valdez got to Mount Diablo, they met the giant Enceladus, who summoned Earthborn straight from the ground. Leo destroyed five of them with construction equipment, and the last one destroyed by Piper. Once they got destroyed, they left some pieces of loincloth behind.

After Jason, Leo, and Piper's helicopter got destroyed, Thalia Grace met up with them. She told them about how they were surrounded now, and then killed one of the Earthborn with her final arrow. Later, Piper and Leo fought the rest of them, and returned all of them to the pits of Tartarus. Unfortunately, after Porphyrion rose, they came back to life.

The Son of Neptune
At least a few dozen Earthborn, and likely many more, were observed by Percy, Frank, and Hazel marching in Polybotes' army on the way to Camp Jupiter.

During the battle at Camp Jupiter they were fired on by the Scorpians but continued to push the Romans back, before Percy and Frank rallied the Fifth and Third cohorts to attack them. A large number of Earthborn were destroyed when Percy used the Eagle to kill a huge number of monsters. The remainder were presumed to have been killed or fled after the battle.

Trivia

 * According to Ella, the groin of an Earthborn is sensitive. It is unknown if this is true or not.