It is an old tradition that has become an excuse to party, drink, and consume unhealthy amounts of crustaceans. But for those who have never been to a crayfish party, it can be a bit confusing as to what exactly is being celebrated.

Jonas Engman, an ethnologist at the Nordic Museum in Stockholm, says that crayfish have been on Swedes' plates for a very long time indeed.

"People have been eating crayfish since the sixteenth century, but it wasn't until the nineteenth century when the parties actually started," he explains. "It was a way to say farewell to summer and welcome to autumn. And August was also the month the crayfish were ready to be fished."

Photo: Christine Olsson/TT 

The consumption of the crayfish grew significantly in the end of the nineteenth century to a point where they were overfished, meaning Sweden needed to draw in the reins instead of the nets. A law came in force that only allowed consumption from August 7th – the kräftpremiären ("The Crayfish Premiere") – through to November 7th.

"But the law was abolished in 1994," Engman explains. "Nowadays the party is usually celebrated throughout August."

Photo: Björn Lindgren/TT

And the Swedes sure know how to celebrate properly. Engman shared the five ingredients for a successful kräftskiva (pronounced kreft-HWEE-va).

1. Crayfish. Without a doubt, the most important ingredient. And make sure they're well prepared, he says. Other Swedish foods that go along with the festivities are Västerbotten cheese and knäckebröd (crispbread).

2. Snapsvisor.  Some would argue that the snapsvisor (traditional drinking songs) are more important than the alcohol itself. These songs are supposed to be sung when taking shots. Engman said that there are many varieties and tunes, and that it's often the students who add new songs to the mix.

One popular snapsvisa is called Helan Går – literally "the whole thing goes". Here are the lyrics in Swedish. 

3. Decorations. The trademark décor found at crayfish parties are round moon faces hanging from the ceiling and walls. "These moon faces most likely mark the fact that summer is getting darker," Engman explains. 

4. Party hats. These are optional but tend to be included, usually with a picture of a crayfish on. Why? Who knows why. Just put your hat on and get on with it. 

5. People. What is party without the people? Engman says that Crayfish parties in Sweden are very similar to Christmas parties in that the whole family tends to get together to celebrate. So make sure you've got plenty of room if you're hosting.

Photo: Fredrik Persson/TT

With that in mind, take on more look at the lyrics above, pour out some aquavit… and skål!