The Invisible Bots Shaping Every Trade You Make on Ethereum

Every time you swap tokens on a decentralized exchange, there’s a reasonable chance a bot is watching. Not just watching — profiting. These are MEV searchers: automated algorithms that scan Ethereum’s mempool for opportunities to reorder, insert, or exploit transactions before a block is confirmed.

MEV — Maximal Extractable Value — is the profit that can be captured by controlling the sequence of transactions in a block. Searchers are the entities that do the hunting.

How it works

Searchers run algorithms that monitor pending transactions in real time. When they spot an opportunity — say, a large token swap that will move a pool’s price — they construct a “bundle”: a carefully ordered set of transactions designed to capture that value. That bundle gets submitted privately to a block builder, which assembles the most profitable block for validators.

The supply chain looks like this: Searcher → Builder → Relay → Validator. Searchers don’t mine or validate anything. Their edge is purely informational and computational.

The four main strategies

DEX arbitrage is the most common and arguably beneficial — bots buy where a token is cheap and sell where it’s expensive, keeping prices consistent across liquidity pools.

Liquidations keep lending protocols like Aave solvent. When a borrower’s collateral drops below the required threshold, searchers race to liquidate it and collect the protocol’s reward.

Sandwich attacks are the most controversial. A bot inserts its own buy order before a large user swap, and a sell order after it — pocketing the price difference the user’s trade created. The user ends up with worse execution without knowing why.

Backrunning sits in between: a bot follows a large trade to capture the resulting price gap between pools, without directly interfering with the original trade.

Good, bad, or both?

Arbitrage and liquidations serve real economic functions — they make DeFi more efficient and prevent lending protocols from accumulating bad debt. Sandwich attacks, on the other hand, extract value directly from users, contributing to roughly $60 million in annual losses on Ethereum alone.

On the validator side, MEV revenue lifts staking yields from around 4% to roughly 5.69%, making the network more secure by making staking more attractive.

The uncomfortable reality: the strategies most profitable for searchers tend to impose the greatest costs on everyday users.

Who actually runs these bots?

The barrier to entry is steep. Competitive MEV searching requires dedicated full-node infrastructure, low-latency simulation engines, private bundle submission pipelines, and servers co-located near Ethereum validators. After paying builders and validators, searchers typically retain less than 10% of gross revenue.

In practice, the market is highly concentrated. One entity — jaredfromsubway.eth — was reportedly responsible for roughly 70% of all sandwich attacks on Ethereum over a tracked study period. New entrants are unlikely to be profitable in saturated strategies.

As MEV infrastructure becomes more sophisticated and concentrated, do you think protocol-level solutions can meaningfully protect ordinary DeFi users — or is some degree of value extraction simply the price of a permissionless market?

Read more: https://cryptothreads.io/learn/what-is-an-mev-searcher/

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