In the beginning of the 20th century, the number of crayfish in Sweden's freshwater rivers began to dwindle due to overfishing. In response, the government instituted countrywide fishing restrictions that bumped the beginning of crayfish season back to Aug. 7 — one reason behind the timing of the traditional late-summer crayfish celebration known as a kräftskiva.

Next Friday, Aug. 5, Philadelphia's American Swedish Historical Museum (ASHM) is hosting its own crayfish party with all of the traditional elements — they'll boil the crayfish in a brine with lots of crown dill, then leave them to sit for a tick before they're cracked open by hand. "Traditionally, [crayfish] are served with crisp toasted bread and a sharp cheese, as well as other sides," says Birgitta Davis, associate director of ASHM. "There's also a liqueur that's usually drunk with the meal called aquavit," a potent caraway-flavored spirit. The menu of the ASHM's annual party, accordingly, will include toasted bread with Swedish cheese, potato salad, green salad and a dessert. There will also be Swedish meatballs with lingonberry jam.

Swedes wear paper hats while eating these crustaceans, though the meaning behind this tradition is unclear. Since the crayfish is meant to be celebrated outdoors at night, paper lanterns that go along with a kräftskiva sport a picture of a moon.

Songs, known as snapsvisa, are often sung before knocking back a shot of aquavit. "They're short, snappy, nonsensical tunes," says ASHM membership director Caroline Rossy. "Most of the songs are about the Norse gods and are just for the fun of singing songs while drinking. We pick someone that looks like they've had some to drink to lead them."

(brian.wilensky@citypaper.net)

Summer Crayfish Party, Fri., Aug. 5, 6:30 p.m., $50, American Swedish Historical Museum, 1900 Pattison Ave., 215-389-1776, americanswedish.org.