If you go for a walk in the woods any time soon, you may still encounter black walnuts or the remains of their hulls on the ground.

Fallen Black Walnuts

The nuts usually remain on the tree until after the leaves fall, reminding me of a Charlie Brown Christmas tree.  Then all the nuts fall within a short time of each other.  These nuts are sweet tasting and highly nutritious.  Studies show that eating them helps prevent cardiovascular disease, diabetes and cancer.  Walnuts have as much protein as an equal weight of beef, but they also contain essential fatty acids that are necessary for healthy brain development and function.  Any aging brains out there?  Eat walnuts!

Black Walnut (Junglans nigra)

Mammals other than humans like them, too: squirrels, mice and voles, for example.

Eastern Gray Squirrels eat and help disperse Walnuts

Red Squirrels also enjoy many tree nuts, including Walnuts

These animals aid in the spread of Walnut trees when they overlook some of the nuts they have hidden away for later use, effectively planting them.

In turn, these animals are food for larger animals, like fox

Red Fox

and raptors.

Red-shouldered Hawks, as well as most other raptors, hunt and eat small mammals

According to Douglas Tallamy in Bringing Nature Home, the leaves of Black Walnut (Juglans nigra) trees and the closely related Butternut (Juglans cinerea) provide food for the caterpillars of over 100 species of moths and butterflies, including Luna Moths and Banded Hairstreaks.

Banded Hairstreak on Butterflyweed. Their caterpillars feed on the leaves of Black Walnut and other woody species

The Walnut Caterpillar specializes on Black Walnut and relatives such as Butternut.  This means the leaves of these trees are the only food these caterpillars can eat.

Walnut Caterpillar (Datana integerrima)

Since they are an important source of food for birds, not all caterpillars will see life as an adult butterfly or moth.

Tufted Titmouse

Black Walnut trees have a reputation for not playing well with other plants. That is, many plants won’t grow successfully in close proximity (within the drip-line or reach of the roots) of a Black Walnut. The reason is more complex than shade and competition for water.  Black Walnuts contain juglone, which is an anti-fungal chemical.  In order to derive nutrients from the soil, the vast majority of plants partner with underground mycorrhizal fungi (think mushroom, not the mold in your shower).  Unless the fungi on which the plant depends is resistant to juglone, or the plant doesn’t require this partnership to obtain its nutrition, that plant won’t do well.  Of course, some plants and their fungi partners have evolved in exactly this way.  Click here for some suggestions from The Mortem Arboretum for plants that can co-habit successfully with Black Walnut trees.

It’s of benefit to Black Walnut trees to produce juglone, since it does reduce competition for resources, and protects the trees from fungal invaders that might do them harm. Juglone also has sedative properties that may aid animals in dormancy. It can even have a calming effect on people.

Black walnut trees contain another compound called ellagic acid in both their nuts and leaves. This compound is thought to help prevent cancer in people who consume the nuts. The ellagic acid in the leaves is effective in removing carcinogenic hydrocarbons from the air, helping to reduce the effects of air pollution.

As if that weren’t enough, Black Walnut’s wood is valuable for furniture and cabinet making, and the nut hulls can be used to make a dye.

Black Walnut with hull partially removed

These are just some of the known benefits of Black Walnut trees.  Just imagine what we don’t know yet!  No wonder ‘juglans’ is sometimes translated as ‘nut of Jupiter’, or ‘nut of the gods’.

Black Walnut Tree (Juglans nigra)

Resources

Beresford-Kroeger, Diana.  Arboretum America: A Philosophy of the Forest.  2003

Eastman, John. The Book of Forest and Thicket. 1992.

Tallamy, Douglas W.  Bringing Nature Home.  2007

Wagner, David L.  Caterpillars of Eastern North America.  2005.

Butterflies and Moths of North America

Natural History Museum Database of Leipidoptera Hostplants