I rank swallows right up at the top with owls and corvids (ravens, crows, magpies, and jays) in terms of their importance in mythology, magickal correspondences, and folklore. 
Swallows can be found all over the globe- every continent except Antarctica. Their diet consists entirely of insects, thus they are migratory- leaving colder climates in winter to chase insects populations to the more balmy southern latitudes. 
Swallows are steeped in folklore. From the carriers of unbaptized souls, to omens and predictors of the weather…swallows have long played a spiritual role in human culture. 
Here are some fascinating tidbits I found about swallows in folklore and their correspondences:  
💙Omens and Weather- Swallows were among the most trusted weather prophets in European tradition. Low-flying swallows foretold rain, while high-flying ones meant fair weather — an observation that actually has some meteorological basis (insects fly lower before storms). From my own experience watching swallows here in north Idaho- this is SPOT ON. 
Their arrival in spring was a powerful omen of good luck, and killing one was considered deeply unlucky, even catastrophic.
🤍Protection and the Home-
Across Britain, Germany, and Scandinavia, swallows nesting in your eaves were considered a powerful blessing. They protected the house from fire, lightning, and evil spirits. Disturbing or destroying their nests invited disaster — the cows might stop giving milk, the crops might fail. This belief was so widespread it functioned almost as law in rural communities. 
It breaks my heart to see people removing the nests they so painstakingly build, one little beak full of mud at a time…. It’s exhausting just thinking of how much care and effort they put into these intricate nests. 
🖤The Soul and the Dead- In many traditions, swallows were believed to carry human souls. In some Slavic and Baltic folklore, they carried the souls of unbaptized children. In parts of Wales and Scotland, they were thought to shelter the souls of the dead, making harming them taboo on a deeply spiritual level.
🪰🦟🪲🦋 Swallows are aerial insectivores, catching insects in their large mouths as they pursue them in the air. Their agile and acrobatic flight helps them pursue flies of all types, along with beetles, bees, wasps, ants, butterflies, moths, and other flying insects.
Globally insect populations appear to be declining at an alarming rate. Abundance of insects has deceased by 70% in some areas in just the last few decades. Swallows are one group of aerial insectivores that are declining across much of the planet.