Americans will spend an estimated $480 million on costumes for their pets this Halloween, more than double what was spent in 2010, according to The National Retail Federation. Pet costumes make up 15% of all Halloween costume sales, with more than 31 million Americans set to buy costumes for their pets this year, up from 28 million last year. Millennials who are 25- to 34-years-old are the most likely to dress up their pets, and often post photos online. Unsurprisingly, Facebook and Instagram appear to be fueling the trend. The top pet costume is a pumpkin, according to the National Retail Federation, followed by a hot dog and a bumble bee.