In ancient times, Samhain and Beltane were the two main festivals of the year, one symbolising death and the other life in all its glory. May eve is the traditional night for young people to indulge in night time revels to encourage fertility back to the land through sympathetic magic.
In the morning people "Welcome in the May". Some bathe their faces in the dawn dew. Some rituals involve the death and regeneration of a ceremonial "Obby Oss" - any woman caught under the Oss is certain to be pregnant within the year. In the South East, Jack in the Green is abroad, and the Green Man elsewhere. And every Morris Dancer worthy of the name dances to welcome in the Summer.
The illustration on the card shows this at Kits Coty in Kent-a modern, very widespread custom reflecting the woodland revels of the past.