Aetna and Humana are certainly hoping their $37 billion combination will get approved, but at least one other company should also be rooting hard for the deal to get done and that's smaller rival WellCare. 

Aetna and Humana dropped on Monday amid reports that the health insurers are facing an increasingly uphill battle to sell their mega-merger to regulators. They're hoping a divestiture of Medicare Advantage policies covering about 350,000 people to either WellCare or a company like it will help make their case. The jury's still out on whether that's going to be enough for the Department of Justice (more on that later), but for WellCare, it's clear a deal would be a boon. 

The $5 billion insurer has largely sat out of the industry's takeover frenzy over the past year. It's relatively small size has meant it's typically been cast in the role of potential target rather than would-be acquirer. WellCare still could draw interest, particularly if Anthem's $50 billion-plus purchase of Cigna falls apart and puts both companies back on the prowl. But if WellCare is going to go it alone, it needs to get bigger.

Among giants

WellCare is the eighth-largest U.S. provider of managed care by revenue, trailing well behind Aetna and Humana.