Option activity was unusually heavy on Tesla Motors, Inc. (NASDAQ:TSLA - 34.62) yesterday, with roughly 8,500 calls and 11,000 puts changing hands on the electric automaker -- representing 2.8 times the stock's average daily volume. Most of the action was driven by longer-term speculators, with two of TSLA's June 2013 options emerging as the day's most active strikes.

Specifically, a total of 5,025 contracts traded at the equity's June 40 call, while 5,000 contracts changed hands at the June 30 put. Upon closer inspection, it looks like one spread strategist was responsible for the heavy volume at these two options. In afternoon trading, two blocks totaling 5,000 contracts crossed at the bid price of $1.55 on the June 40 call, while two matching blocks of 5,000 simultaneously traded at the ask price of $4.50 on the June 30 put. All of these contracts translated into new open interest overnight, confirming that new positions were initiated at both strikes.

Since the calls traded at the bid price and the puts changed hands at the ask price, we can speculate that the calls were sold to open and the puts were bought to open. With TSLA trading squarely between the two strike prices in question, this may have been the initiation of a collar spread.

In this strategy, a shareholder simultaneously buys out-of-the-money puts and sells out-of-the-money calls in order to lock in favorable exit prices on his stock. This tactic is typically used when the shareholder is not yet ready to unload his shares outright, but is nervous about a potential pullback eroding his paper profits.

TSLA has strung together a healthy year-to-date gain of 21.2%, but the stock is now trading just below the $35 level. Historically, the mid-30s have been a sticking point for TSLA going back to November 2010 -- though the shares enjoyed a brief breakout to the $40 neighborhood in late March 2012.