Updated from 3:25 p.m. ET to include additional information about what sectors have seen the most insider selling.NEW YORK ( TheStreet) -- October has seen plenty of insiders selling and very few buying, according to data from research firm TrimTabs, which tracks asset flows and market liquidity. So far this month, insider selling is averaging $178 million worth of transactions per day, the firm said. That's more than double September's daily average of $76 million. Meanwhile, insider buying has been "almost non-existent," TrimTabs notes, coming in at just $8 million per day, less than a third of the year-to-date average of $30 million. "As the S&P 500 has climbed 12.6% from its closing low on October 3, insider activity has turned extremely bearish," the firm said. Those numbers result in an insider sell/buy ratio of 21.5 for October, up significantly from ratios of 2.4 in August and 3.1 in September, and the highest level seen since February. TrimTabs said the sectors seeing the most insider sales so far this month are consumer discretionary at $1.00 billion, health care at $451 million, and information technology at $204 million. Month-to-date, selling is still below $3 billion but the activity has already exceeded September's total. From a dollar value standpoint, insider selling for 2011 peaked in March, when it exceeded $13 billion. Among the companies seeing insider sales this month have been Apple ( AAPL), Ciena ( CIEN), Crocs ( CROX), CBS Corp. ( CBS), Ann Inc. ( ANN), Leapfrog Enterprises ( LF), and SanDisk ( SNDK), to name just a few. In a Form 4 filed on Oct. 20, Jeffrey Williams, a senior vice president at Apple, details the sales of 10,000 shares received on Oct. 18 following the vesting of restricted stock units. Williams sold 4,668 shares on Oct. 18 at the stock's closing price of $422.24 then sold the remainder on Oct. 19 at prices ranging from $399.55 to $407.86. Williams still owned 213 Apple shares following the transactions, according to the filing. On Oct. 17 Stephen Alexander, senior vice president and chief technology officer at Ciena, sold 3,500 shares at $12.22 each. Alexander still owns more than 225,000 Ciena shares, according to the filing. A well-timed sale was executed by Daniel Hart, executive vice president at Crocs, as part of regular options vesting and stock sale activity. Hart exercised an option to acquire 4,167 Crocs shares at $3.99 each on Oct. 17, and sold the same amount of stock the same day for $26.93 per share. After the market close that day, Crocs issued a surprise warning for its third-quarter results, sending the stock down more than $10 on Oct. 18 to close at $16.15. Hart's sale though was in keeping with past practices as he been executing similar monthly transactions of varying sizes for more than a year. Hart also still beneficially owns more than 100,000 Crocs shares, so he's taken a hit as well.