Willow Trees

Willow trees are great for pollinators.

A willow tree is a type of tree that grows along rivers and streams. It has long, flexible branches that typically reach over the water. The bark of the willow is a light brown color. The leaves are shaped like ovals with serrated edges, are green in color, and they curl up inwards towards the stalk when they fall off from the tree during Autumn season.

Willows are known to grow up to 100 feet depending on species; willow trees prefer full sun and tolerate many soil types.

Salicylic acid is a naturally-occurring plant hormone found in the willow tree. The willow tree has been used medicinally for centuries, especially by Indigenous populations. For example, willow bark tea is made by steeping willow bark in boiling water, and it’s been shown to have analgesic properties. Salicylic acid is a precursor to acetylsalicylic acid (ASA), which you probably know better as aspirin.

It belongs to the order Salicales, family Salicaceae, and the genus is Salix. The number of species in Salix currently stands at approximately 400, and this includes deciduous trees and shrubs.

Willows are hosts to more than a hundred aphid species.

Some lesser known butterfly and moth species that Salix supports in North America include:

• Pistol casebearer – Coleophora multipulvella
• Sallow clearwing – Synanthedon flaviventris
• Willow ghost moth – Sthenopis thule
• Cherry casebearer moth – Coleophora pruniella
• Giant leopard moth – Hypercompe scribonia
• Coleophora kearfottella
• Batrachedra salicipomenella
• Coleophora salicivorella
• Batrachedra striolata

But you probably know some of these:

The mourning cloak (Nymphalis antiopa) butterfly is a large brownish-red butterfly with black and white markings. The adult has two broods per year. The immature form of this species is sometimes known as the spiny elm caterpillar.

The viceroy (Limenitis archippus) is a large orange and black butterfly that is frequently mistaken for a monarch. The caterpillars sequester salicylic acid in their bodies, which makes them bitter, and distasteful to predators.

The white admiral (Limenitis arthemis arthemis) and red spotted purple (Limenitis arthemis astyanax) also feed on willows (and birch trees) as caterpillars.

Remember to plant only the willows native to North America. For instance, weeping willow is native to China, but black willow is native to this continent.