Universal's Halloween Horror Nights. Source: Rick Munarriz.

October used to be a quiet time of the year for the theme-park industry. Summer tourists are back in school. The year-end holidays are two months away. Outside of a busy slate of conventions, it's a seasonally sleepy month.

Halloween has changed all that. The holiday's been around for a long time, but we're seeing the theme-park industry embrace Halloween with ghoulish gusto. 

Disney (NYSE:DIS) and Universal Studios' parent Comcast (UNKNOWN:CMCSK.DL) (NASDAQ:CMCSA) offer Halloween-themed events at their theme parks on both coasts. Regional amusement parks that used to shut down in September are also seizing the opportunity to smoke out another few weekends more out of the operating calendar by hosting haunted houses and other after-hours events. 

Halloween festivities seem to expand with every passing year. Disney and Universal kicked off their Halloween events in mid-September this year. If you think that's a bit early to go trick-or-treating with Mickey Mouse, or to be walking hesitantly through a Universal scare zone, how about bleeding past October?

On Tuesday, we saw Universal Studios in California announce that it would be extending its Hollywood Horror Nights event through Nov. 7.

One can argue that the parks are merely giving customers what they want. Disney World's Mickey's Not-So-Scary Halloween Party is sold out for all four nights left of the final week. Universal Orlando's Halloween Horror Nights rarely sells out, but with folks visiting on a busy night, waiting as long as two hours to go through one of the nine haunted houses, it's hard to classify it as anything other than a rousing success.

This is a goldmine that's more treat than trick for investors of the theme-park operators. These are hard-ticket events. The parks close early, but they still get a healthy flow of day guests. The parks then charge extra for the nighttime events. Disney's Mickey's Not-So-Scary Halloween Party will set you back $74 -- if it hasn't sold out -- and Universal Orlando's Halloween Horror Nights peak at $77 a night on Saturdays. 

That's really just the beginning. If the lines for Universal Orlando's houses are too long, you can pay $70 for an Express Pass, which cuts the wait time by at least half. If you don't want to wait at all, the RIP Tour is a guided tour that walks you into all nine houses with a break at a private cash bar. The tour starts at $140 per person. Even if you decide to rough it out with the common folk, you'll be tempted to purchase specialty drinks being peddled by bloodied nurses toting IV packs. All of the events also offer event-specific merchandise. 

In short, Halloween is giving theme-park and regional amusement-park operators a license to print money in October. Scaring is caring.