Spring is finally among us, here are some of the key indicators of the season.From April to May, our woodlands become daubed in a riot of purple as bluebells briefly cast their spell. The flowers seem to prefer oak woodlands, but can also be seen on coastal cliffs in some locations.The brimstone, a delicate pale yellow insect, is one of the first butterflies to emerge following the winter. The word butterfly is thought to be derived from the brimstone, due to its butter-coloured appearance.Swifts and swallows return with the summer sun, but some of our migrants are already home. Look in fields for wheatears, smart blue/grey-backed, thrush-sized birds. Early warblers will also be skulking about once again, so listen for the onomatopoeic call of the chiffchaff.Read