Magician trading floorReuters/Kai Pfaffenbach
Millennials are big users of some of the most speculative investing instruments in the stock market, according to TD Ameritrade.
The brokerage firm told Business Insider that the roughly 18-35-year-old demographic made up about 40% of its new customers. Almost half of their trades came from mobile devices, said Victor Jones, the director of trading at TD Ameritrade. 
"Trades from mobile tend to be more futures-based," Jones said. "More people are gravitating towards derivatives like options and futures." 
"When you have your phone on you, you're available to look at the markets 24/7, but the markets aren't open 24/7," Jones said. "Futures give millennials or any investor the opportunity to participate in the market 24/7."
Instead of buying a specific asset class like a company's stock or a currency, futures and options contracts allow traders to profit from their bets on future prices and to hedge losses on what they already own.
Jones doesn't see mobile trading as the reason why more people are moving towards derivatives that aren't tied to the 9:30 a.m. to 4 p.m. ET stock-market schedule.
More investors — millennial and older — understand they can use these instruments to manage portfolio risks, Jones said. Derivatives trading made up about 45% of TD Ameritrade's transactions, he said, up from about 10% in 2009.
"They're gravitating towards the trading strategies that can help them limit their risk, limit their capital exposure, and generate additional yield on the portfolio," Jones said. 
Coincidentally, Interactive Brokers had captured this in a TV commercial in which a woman interrupts her dinner with a man to "do some hedging trades" on her phone because global markets are crashing after Russia downed a NATO plane.  
Even as derivatives trading may demonstrate a certain sophistication among millennial traders, it could also reflect their outsized stomach for risk, since they have a longer runway to earn returns from the market. A TD Ameritrade spokesperson said the most popular options strategies included covered calls, through which a trader can hedge on a long position in an asset. The options education page was consistently among the firm's top-five most visited, she added.
"I agree that derivatives do have unique risk characteristics," Jones said. "We are passionate about ensuring that our clients are aware of the unique risk characteristics."