Stocks tumbled again Monday, with tech companies getting hit particularly hard.

The Dow Jones industrial average and the S&P 500 were lower at midday. Strong earnings from Dow component Caterpillar (CAT, Fortune 500) helped to keep the broader market’s losses at a minimum. Shares were up 4% after the construction equipment company easily blew past earnings and sales estimates, and approved a new $10 billion stock buyback program.

But the Nasdaq was down more than 1% andCNNMoney’s Tech 30 index also fell. Shares ofTwitter (TWTR) plunged. Fellow social media companies Facebook (FB, Fortune 500) andLinkedIn (LNKD) also were markedly lower, as was online streaming giant Netflix (NFLX).

The Nasdaq was also dragged lower by biotechnology companies such as Celgene (CELG, Fortune 500)and Alexion Pharmaceuticals (ALXN). The PowerShares QQQ Trust (QQQ), a widely-held exchange-traded fund that tracks the Nasdaq 100, is now down more than 2% for the year. And some are worried that the ETF will fall even further.

“$QQQ is teetering on the edge. We may see a sizable correction begin to unfold,” said StockTwits user OptionsElite.

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