If you haven't remembered to buy your dog his costume yet, here's something else you may have overlooked:

Americans are expected to spend $3.12 billion on Halloween this year.

I started thinking about this the other day after I picked up a pet store ad, wondering if my cat's favorite food might be on sale, and noticed a picture of a woman smiling maternally and cuddling a little dog, which happened to be wearing a bumblebee costume.

Naturally, I went right to the computer and Googled pet costumes. Up came a long list of sellers willing to turn your dog into Dracula or my cat into a hula dancer, including Petsmart, Petco and, for catalogue shoppers, Lillian Vernon.

Operating on the principle of seeing is believing -- and in need of cat food at any price -- I headed over to the closest pet-supply warehouse, where a helpful dog trainer told me that they had been doing a nice business in pet costumes for the last couple of years.

She gave me an invitation to the store's costume party -- there's a dog in skunk costume on the front -- and assured me that cats were most welcome. Last year, she said, two self-possessed cats had come dressed as Minnie and Mickey Mouse. Yes, she conceded, the costumes are tailored for dogs because more dogs than cats are willing to please their owners by putting on a costume, but a cat in the right frame of mind can wear a costume made for a small dog.

Some owners, she said, make their own spectacular costumes. Last year's favorite was a greyhound dressed as a parrot, with lovely plumage.

If we've started buying costumes for our pets, and taking them to trick-or-treat parties, it's no wonder Halloween has turned into the nation's sixth-biggest spending holiday, after Father's Day ($8.04 billion), Mother's Day ($10.43 billion), Easter ($10.47 billion), Valentine's Day ($12.79 billion) and the winter troika of Christmas, Hanukah and Kwanzaa ($219.9 billion). Halloween is far behind the others -- we're not buying golf sweaters or dozens of roses, yet -- but $3.12 billion is still a lot of candy corn.

These figures are from Ellen Tolley, who as spokeswoman for the National Retail Federation keeps up on how much we're spending for what. It stands to reason, she said, that if a business is going to grow, it's got to find new things to sell.

"The Halloween welcome mat won't do it anymore," Tolley said, "so retailers have to think outside the box."

This desire to expand comes at a time when people are spending more on their pets in general, she said.

So, while you can find plenty of Halloween doormats and candles everywhere, you'll also find pet stores selling spooky collars, spider toys for cats and cat costumes for dogs. You'll find department stores selling Halloween scarves and socks. And you'll find discount stores stocked with ready-made scarecrows, gingerbread-castle kits, an eight-foot Scooby or Pooh for the lawn, flags, plastic gates and arches already fluttering with bats, enough spooky lights to scare the whole neighborhood, fog machines, Styrofoam tombstones, tablecloths, runners, napkins, soap dispensers, platters, plastic pumpkins, felt pumpkins, glass pumpkins and even real pumpkins.

And candy. Veritable mountains of candy. And costumes, for babies, toddlers, kids, adults. And greeting cards. (To the dog. To the cat. From the dog. From the cat. Cute. Off-color. Woman to woman. To Godchild. From Secret Pal. Sister. Grandpa. Great-grandma.) And don't forget the big orange-and-black plastic bins in which to store it all.

It's enough to make you shriek, and spend the Halloween average of $43.57.

And that's exactly what more and more grown-ups are doing, Tolley said.

"Halloween used to be a holiday just for children," she said. "In the last decade it's shifted from a holiday for kids to one for young single adults as well. Many people have very favorable memories of dressing up. A lot of young adults don't want to relinquish Halloween and all those wonderful memories."

When NRF did its Halloween survey recently, it found that more than 69 percent of 18- to 34-year-olds planned to celebrate, with half of the 18-to-24 age group intending to dress up in a costume. They're not trick-or-treating, they're giving or going to a party.

My own young adults -- two college-student daughters -- confirm this. They've always loved Halloween and see no reason growing up should interfere. Kate, 22, said Halloween has all the best holiday attributes, plus skeletons and ghosts.

"There's candy involved, you don't have to travel anywhere, and people who normally look the same look different," she said.

Wearing a Halloween costume, Kate said, gives you license to be anything. "It's not as if the costume represents your inner consciousness," she said, "but it can reflect a side of your personality."

Judging from the costumes in the stores, kids this year haven't changed much in what they want to be. There are plenty of witch hats, devil horns, angel wings, clown noses and pirate eye patches to be had.

But this year's big costume will be Spider-Man, Tolley said, driven by buzz from the "Spider-Man 2" movie and the inspiration of the everyday guy who can be something he's not. The NRF survey found that 2.15 million children were planning to dress up as Spidey, who will be accompanied by 1.8 million princesses.

"The pop culture can only do so much," Tolley said. "The princess reigns."

Give me my $43.57. The cat's staying home. I'm going shopping.

There's a nice vampire coffin I've had my eye on.

Washington pooch as pig, with a costume from Doggie Style, on 18th Street NW.