KOMAKI, Japan — It's springtime in Japan and that means one thing.

Actually, two things. Penis festivals and vagina festivals.

It may sound like a sophomoric gag. But these are folk rites going back at least 1,500 years, into Japan's agricultural past. They're held to ensure a good harvest and promote baby-making.

Maybe they should hold more such festivals. Japan has one of the world's lowest birthrates (1.37 children per woman), which experts blame on stagnant incomes and changing gender relations.

The center-left government that came to power last year hopes to make child-rearing more affordable with a $280 monthly stipend per kid.

Meanwhile, the festivals provide an economic shot in the arm for host cities, a party for foreign tourists and expats, and a chance for locals to let loose, too.

One of the best-known penis festivals is at Komaki City's Tagata shrine, about 45 minutes outside Nagoya, every March 15. In a neighboring village, a vagina festival is held the Sunday before that. This year, that was the 14th — meaning rare, back-to-back genital worship days.

At the Hime-no-miya grand vagina festival, parents dress up their kids, pray for healthy babies, and celebrate with sake, beer and snacks galore.

In the morning, children carry a small vagina to the Ogata shrine. Later, some 40 grown men strain under the weight of a massive vagina while carrying it to the shrine in the main parade. They're followed by two smaller vagina litters.

At the end of the day pink and white mochi (glutinous rice ball treats) are hurled into the crowd.

The penis festival the following day drew far more foreign and Japanese tourists — some 100,000, according to a festival brochure. Festival foreplay included much posing with wooden and candy penises. The main event is the parading of a two-foot by six-and-a-half foot long phallus carved from Japanese cypress.

Teams of men strain under the weight, stopping to spin the penis around a few times amid yelling, cheering and jostling. The work is so hard that teams rotate during the one-and-a-half hour procession.

This phallus parade is rooted, says the brochure, in "an ancient Japanese belief that for the growth and development of all things, the mother, earth, has to be impregnated by the father, heaven."

"People come here when they want to have a baby," said festival volunteer and Komaki resident Katsuragawa Noboru. "If it works, they have to come back the next year to thank the gods."

It worked for Katsuragawa, twice: He has a son and a daughter now, he said with a laugh.

Lucy Glasspool, who researches gender and pop culture as a visiting scholar in Nagoya, was helping out at the information booth. It was her first penis festival.

"I heard about this a long time ago and I'm not sure I believed it," she said. "But now I'm here and it's everything I thought it would be. I highly recommend the penis-shaped candy."

She gave English-language updates on the penis' progress through a microphone, and passed out detailed information in English on the history and significance of the rite. But most Western tourists seemed happy enough just to drink beer and make endless penis jokes.

Vendors sell penis- and vagina-shaped candies and chocolate-covered bananas, wood penis sculptures and penis earrings, adding to the mirth. Eavesdropping was a riot.

Said one American woman into a cell phone, in a southern twang: "We just found an ashtray that's in the shape of a vagina that you need to buy."

"It's smaller than last year's," one jaded female expat loudly complained, as the phallus approached.

One American woman, reviewing a photo of her friends posing with penis-candy-sucking Japanese, said, "Oh my God. This one is so going on Facebook."