Selected bits from Interactive Broker's latest 10-K, bold [and comments in brackets] are mine:
"Market Making—Timber Hill ... Most of the above trading activities take place on exchanges and all securities and commodities that we trade are cleared by exchange owned or authorized clearing houses. Recently, the emergence of High Frequency Traders and others who compete with us but do not regularly provide liquidity [zing!] have put our market making operations under pressure and its relative significance has diminished."
...
"Market Making
Historically, competition has come from registered market making firms which range from sole proprietors with very limited resources to large, integrated broker-dealers. Today, Timber Hill's major competitors continue to be large broker-dealers, such as Goldman Sachs, Morgan Stanley, UBS, Citigroup, Bank of America Merrill Lynch, and niche players such as Citadel, Susquehanna, Virtu, Wolverine Trading, Group One Trading, Peak6 and Knight Capital Group. Some of our competitors in market making are larger than we are and have more captive order flow, although this is less true with respect to our narrow focus on options, futures and ETFs listed on electronic exchanges.
The competitive environment for market makers has evolved considerably in the past several years, most notably with the rise in high frequency trading firms ("HFTs"), which transact significant trading volume on electronic exchanges by using complex algorithms and high speed execution software that analyzes market conditions. HFTs that are not registered market makers operate with fewer regulatory restrictions and are able to move more quickly and trade more cheaply. This issue is currently an area of focus amongst regulators who are examining the practices of HFTs and their impact on market structure."
...
"We face competition in our market making activities.
In our market making activities, we compete with other firms based on our ability to provide liquidity at competitive prices and to attract order flow. These firms include registered market makers as well as high frequency trading firms ("HFTs") that act as market makers. Both types of competitors range from sole proprietors with very limited resources to a few highly sophisticated groups which have substantially greater financial and other resources, including research and development personnel, than we do [you mean the "niche players" listed above?]. These larger and better capitalized competitors may be better able to respond to changes in the market making industry, to compete for skilled professionals [better nerds], to finance acquisitions, to fund internal growth and to compete for market share generally.
HFTs that are not registered market makers have certain advantages over registered market making firms that may allow them to bypass regulatory restrictions and trade more quickly and cheaply than registered market makers at some exchanges. We may not be able to compete effectively against HFTs or market makers with greater financial resources, and our failure to do so could materially and adversely affect our business, financial condition and results of operations. As in the past, we may in the future face enhanced competition, resulting in narrowing bid/offer spreads in the marketplace [aren't narrowing spreads good for the little guy?] that may adversely impact our financial performance. This is especially likely if HFTs continue to receive advantages in capturing order flow or if others can acquire systems that enable them to predict markets or process trades more efficiently than we can."
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"Market making segment results declined in 2014 due to the continuation of a difficult operating environment for market makers with strong competition from high frequency traders (HFT's) and historically low volatility levels, which depressed our trading gains."