Corresponds to month of Maius on the old Roman calendar, which was named
after Maia Majesta, the Roman goddess of Spring. On May 1st, the Vulcan priests
made sacrifices to her. In Greek mythology, she was the oldest of the Pleiades,
the seven daughters of Atlas and Pleione, the Oceanid. In a Cyllene cave,
she became the mother of Mercury (or Hermes) through Zeus.

1 May Day
Bona Dea,
Floralia, Starts Apr 27
Beltane, when plants are in full growth, a time of mystical union.
Maia- Roman Goddess of springtime associated with the Earth-Goddess Terra.
Laribius The celebration of the Lares Praestites
National Day of Prayer--Day to pray for freedom of expression, freedom of religion, and separation of church and state throughout the world.
Zuni Green Corn Dance
Iroquois corn planting ceremony
Festival of Bast
2 Floralia,
Elena’s Day-or Helen, the goddess of the holy road. She is Elaine of Arthurian romances. The Welsh Sarn Helen are her roads.
Ysahodhara (Consort of Buddha)
3 Thargelion Noumenia
Greek festival honoring all the Gods and Goddess
Feast of Hecate
4 Bona Dea eve  the Fire festival the Roman good goddess.  This is the anniversary of the dedication of Her temple on the Aventine. The ritual is celebrated only by women; men are excluded,
Festival of Shelia Na Gig (Irish)
Festival of Cerridwen
Festival of Bridgit
Fairy Day
5 Bona Dea, veneration of the thorn,
The Hawthorn tree of the good goddess is honored this day.
Cinco De Mayo
All Mexican and Central American Rain-Goddesses,
Feast of the Dragon
Children’s Day (Japan)
6 Feast of Greek Deities Aphrodite and Eros--Day to honor love and passion
7  Druid feast of Earth Spirits
8 Helston furry dance- A floral dance traditionally performed at Helston in Cornwall  
Horned God
9  Lemuria   Roman festival when the hungry spirits of dead family members might visit their former houses. The Lemuria is held on odd-numbered days because even-numbered days are considered unlucky. It is a festival designed to honor the Lemures, they are regarded as baleful spirits of the dead who died violent or otherwise untimely deaths.
Feast of Ipipi
10  Shiva and Meenakshi,
Tin Hau (Chinese Goddess of the North Star)
11 Mania-  Sacred to Mania, a Goddess of Death and mother of the Lares. When a family was threatened with danger, they often hung effigies of Mania from the front door of the house. On this day she receives sacrifices of these images, characterized by small ugly faces.
Days of the Ice Saints
12 The Celtic tree month of Saille ends.
St. Pancras
Aranya Sashti(Indian God of Woodlands),
The Cat Parade
13 Lemuria, the final day of the Roman festival
Celtic tree month of Huath begins
Argea (Greek) 13-15
14 The runic half month of Ing begins, Ing is the male consort of the earth mother goddess. His rune is the symbol of light.
This month embodies the energy and growth of midsummer,
Festival of the midnight sun
15 Mercurius  this is traditionally the birthday of the Patron of Merchants (this day is also sacred to Maia, his mother). Merchants draw water from the aqua Mercurii — a sacred spring tied to Mercurius — in jars cleansed by fumigation. With a bough of laurel, the merchant then sprinkles both his merchandise and himself with water from the jars. Mercurius is closely associated with merchants and traders, and they hold this day as a feast day.
Maia, Today is sacred to Maia and her son Mercury, and to Vesa, the goddess of the hearth.
Cold Sophie,
Ides of May, the Vestil Virgins of Rome performed a rite to ensure the supply of water for the coming year. 
Scottish quarter day
Rain Dance Night (Guatemala)
16 Brendan the Navigator's day.
The goddess month of Hera begins-Greek goddess, the daughter of Cronus and Rhea. She is said to protect all women who have not slept with her husband Zeus.
17 Dea Dia- festival of the mother of the universe.
18 Feast of Greek God Pan, who represents the masculine in Nature and protects men throughout their lives. Men recognized the transitions in their lives and honored male fertility.
Apollon Day
Today is the festival of the Greek and Roman god Apollo,
the patron of archery, agriculture, animal husbandry, crops, cattle,
farmers, shepherds, sheep, poetry, medicine, prophesy and ethics.
Feast of the Horned God
Feast of the Twins
19  Festival of Bridgid  Old Celtic/Irish feast in which sacred healing wells and springs were adorned with flowers 
Kallyntaria and Plynteria (Greek)
20  Festival of Mjollnir, Thor's hammer
Tradition holds that this is a good day for ritual contests and battle.
Victoria Day
22 Ragnar Lodbrok
23 Rosalia , the Roman festival of roses, in honor of the goddess Flora.
24 Feast of the Mothers- Celtic festival of the three mother goddesses (Goddess of the Moon and the Seasons), who bring prosperity and a full harvest and marking the transformation of the Virgin into the Mother.
Birth of Artemis/ Diana
Feast of Hermes Trismegistus, the patron of alchemists.
25 Fortuna  Sacred to Fortuna, Goddess of fate, chance, luck, and fortune.
Celebration of the Tao-mother of the world (Chinese and Japanese)
26 Sacred Well Day.
27 Festival of Diana,
The Three Fates
28 Python(Greek Serpent-Goddess)
29 Ambarvalia, sacred to Ceres, the goddess of grain, growing plants and the love of a mother for her child.  It's a time of  ritual purification of the fields.  It is the "beating of the bounds", when the boundaries between fields were purified by a procession of sacrificial animals, the suovetaurilia.
Oak Apple day,
The runic half-month of Odal begins- The rune Odel signifies ancestral property.
Iroquois Strawberry Festival
30  Feast of Mary.
The festival of the Norse goddess Frigg, the queen of heaven and consort to Odin, or Wotan
Feast of the Queen of the Underwold
Whitsunday for brewing Whitsun ale and for creating love-bowers.
31 European feast of the Triple Goddess (Goddess of the Moon and the Seasons), marking the transformation of the Virgin into the Mother.
Triple Blessing of Buddha
Celebration of Proserpine and Pluto
Iroquois Strawberry ceremony