What You Learn by Looking at Your Feet: Alder Flea Beetle

alder leaf small

Skeletonized alder leaf

Werner Herzog said, “The world reveals itself to those who travel on foot”.  Taken figuratively, walking encourages reflective, creative thinking that can reveal the true nature of things that bedevil us.  Literally speaking, walking allows us to slowly take in our surroundings in ways that cannot be noticed, experienced or sensed with speedier forms of travel.

This post is about what I notice when walking and hiking: things I learn by looking at my feet.  I enjoy a good walk, whether in my neighborhood, or on a mountain trail. When hiking, the terrain is changing, unstable, and often steep.  Thus, looking down is mandatory for sure footing and safety.  On a paved street, following one’s feet is a more meditative exercise–seeing and feeling the uniformity of steps and the stretch of pavement.

In watching my feet as I plod along, I discover things–keys to learning and wonder.  What can you see at your feet? Roots, plants, fallen leaves, soil, rocks, fungi, insects.  What one sees under their boots doesn’t just inform about what is below, but what is above and all around.  For instance, a fallen leaf, fruit or cone is an identifier of the species of trees whose towering canopy is too high above to see well.

The quality and make up of the soil, rocks, penetration of roots and the level of moisture on which I tread says things about hydrology and geology.  When hiking around Mt. St. Helens last week, the trails revealed pumice, ash, and tenacious pioneer plant species like lupine (introducing nutrients to build the soil for a new forest). Under my feet was a demonstration of the power and beauty of natural forces.

alder sky small

Chewed and skeletonized alder leaves

One of the things I have learned this summer by looking down, is to recognize Alder Leaf Beetle.  My neighborhood walk is punctuated by many lovely Red Alder (Alnus rubra) trees whose fallen leaves–some still green, others totally brown and crisp– were skeletonized.  An insect had eaten the tender tissues only, leaving a lacey framework of veins.  I gazed into the canopy to witness most leaves etched out; the silhouette of ragged patterns remarkably artistic against the sky on all the alders I came upon for 2 miles.

Up until this week, I had not actually seen the culprit itself on my regular walks, only their damage.  But to my elation, on a shady, tree covered stretch, I noticed an army of tiny black crawlers barely perceptible on the dark asphalt.  I crouched down to collect some for identification.

larvae small

Alder flea beetle larvae–about 1/4 of an inch long

I typed “WSU Red Alder leaf pest” into the search engine (using “WSU” in an initial search is my tactic to bring up local, science-based info, with “edu” bringing up a broader set of sources) and I found several links with pictures and descriptions of the Alder (Alnus) Flea Beetle (Macrohaltica ambiens).  I was able to confirm that this indeed was the mystery skeletonizer.  Lucky chance, as it very well could have been an altogether different insect that wasn’t responsible for what I had been seeing, or something less common and harder to research.

A good link from the US Forest Service (a nice source for research-based information) refers to the Alder flea beetle as a “Forest Defoliator” found also on willows and sometimes poplars.  The adult beetle is tiny (up to a quarter of an inch long), shiny, and blackish-blue and chews larger holes in the leaves.  I still haven’t witnessed the adult form. It was the wee, black larvae on the move amongst my footsteps that answered my gentle query, “what’s eating the alders?”  The larvae are the skeletonizers–devouring the tender tissue of the upper leaf surface between the veins.

The Alder flea beetle doesn’t typically harm the alders, even when they are in great enough number to completely defoliate a tree, which happens rarely.  According to the USFS Management Guide for Alder Flea Beetle: “Some have suggested that outbreaks of this insect are actually beneficial by reducing the amount of cover on a site and enabling regenerating tree species to receive direct sunlight.”  Another thing I learned through looking at my feet!

To see images of the adult Alder flea beetle, and to learn more:

USFS Management Guide for Alder Flea Beetle

Pacific Northwest Pest Management Handbook Alder (Alnus) Flea Beetle

About Colleen Miko

Colleen Miko is a certified professional horticulturist with 20 years experience in landscape design who has designed award winning gardens for the NW Flower & Garden Show as well as HGTV’s “Landscaper’s Challenge”. Colleen is freelance garden writer and speaker.
This entry was posted in Garden Pests, Invaluable Invertebrates, Nature and tagged , , , , , , . Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s