LOS ANGELES - Wally the Welsh corgi used to get dressed up to go trick-or-treating for Halloween, often as a banana, once as a dinosaur.

But Wally, owned by Marc and Cynthia Dalangin of Wharton, New Jersey, doesn't go trick-or-treating anymore. Like a lot of busy dogs, he has too many other engagements. And as a budding Instagram celebrity, he needs a wardrobe full of costumes to choose from.As dogs have filled their social calendars, they've had to fill their closets too. They're not just dressing up once a year on Halloween.These days, dogs and their owners are getting invited to parties, parades, meet-ups, pumpkin patches, picnics, Christmas tree farms and many other themed outings.As a result, canine costumes have become more than just something dogs wear once to a party. It's essential for dogs and cats who are up-and-coming social media celebrities to have a varied wardrobe.With their likes and followers growing faster than speeding bullets, their fans want new photos all the time.Two years ago, Wally left the simple banana costume behind when he underwent a lifestyle and wardrobe makeover. Now he dresses like Elvis Presley ("King Corgi") and Michael Jackson ("Thriller Corgi") and has become a rising star on Instagram, with 63,000 followers, and Facebook, with 12,000 likes.Wally's transformation coincides with the pet costume industry's coming of age. And business is booming.The National Retail Federation estimates that 20 million pet owners will dress their pets this Halloween, spending $350 million on the costumes.The online marketplace eBay had 1.5 million pet costumes for sale on Oct. 21 out of 800 million items listed for sale, with 159 million active customers in 200 countries, said Zoher Karu, vice president of global optimization and data for eBay.Pet costumes represent 2 percent of Costume SuperCenter's sales. The company sells nothing but costumes and accessories on eBay and other sites."There does not seem to be a ceiling on what people are willing to spend on their pets," said Michael Esposito, the company's business development and affiliate marketing director.The majority of their pet costumes sell for $14.99 to $24.99. You would never know the costume only required a 10th of the fabric needed for a human costume, he said."Costume SuperCenter has seen its pet costume sales double every year for the last three years," Esposito said. He expects the trend to continue.Halloween costumes for pets and people tend to follow news headlines and movies. The latest "Star Wars" movie isn't out yet but demand is already high for Darth Vader and Yoda costumes."In March next year, Batman and Superman - two of the most iconic superheroes - will face off on the big screen, but we are already seeing the competition play out in stores and online this Halloween season with these two costumes neck-and-neck, topping our best-selling list," said Eran Cohen, chief customer experience officer for PetSmart.