This article develops a taxonomy of stablecoin activity on the Ethereum blockchain. Using all ERC-20 transfers for USDT, USDC, and DAI for the period 2021–2025, we filter noise, Maximal Extractable Value (MEV) signatures and wash-like behaviours, then map the filtered transactions into directed networks and Louvain communities. We show that stablecoin usage cannot be reduced to manipulations and confirm that stablecoins are mainly settlement layers for crypto markets rather than transactional instruments. We also document institutional centralization for exchanges and competitive concentration for DeFi and fintech, highlighting that structural decentralization and economic decentralization are distinct dimensions of stablecoin network dynamics.