Harvesters

A four-legged Ravager.
All Aggressors that appeared prior would attack humans indiscriminately,
but Harvesters extend arms out from their dome-shaped base to capture them.
Captured humans are stored alive in one of their numerous cells.

For this reason, soldiers battling Harvesters ideally want to avoid attacking the capsules, but its tiny head, believed to be its weak spot, is in constant motion, making it difficult to aim at.
Because battling them often results in friendly fire against fellow humans, combat with Harvesters results in severe psychological trauma for EDF soldiers.
There are several theories as to why they capture humans, some believing that they use them as hostages or as shielding from EDF attacks, while others believe they are taken as guinea pigs for experimentation, but the truth remains a mystery.
No captured soldier has ever made it back alive.