More than 40 third-party candidates in pivotal House and Senate races across the country are receiving support from outside super PACs, many of which have ties to the two major parties, an Axios analysis has found.

Why it matters: The sums being thrown around, which total more than $16.5 million, are far greater than virtually any of those candidates have raised or spent on their own.

The super PACs have spent an average of $375,000 more than the third-party candidates they are supporting. More than half of the 43 candidates haven't filed any financial paperwork with the Federal Election Commission.

While it is a comparative drop in the bucket for a midterm that has already seen billions in ad spending nationally, the money will likely play an outsized role in races that are set to be decided by razor-thin margins.

Those races, in turn, will help decide the balance of power in Congress next year.

The top spenders nationwide have been a pair of obscure groups which, like many of the other "pop-up" super…