My Trees Have Fleas

Tiny, iridescent blue and green Alder Flea Beetles on the bark of my alder tree

Living this far into the great white north, we've never had a problem with fleas on our dogs. But this year we have fleas on our trees instead. Our new fleas are small but very handsome, in shimmering shades of iridescent blue and green.

A clump of trees along the lakeshore is currently enduring an outbreak of Alder Flea Beetles (Macrohaltica ambiens or Altica ambiens, depending on who you read). Flea Beetles are small leaf beetles (less than 1/4 inch long) that sport enlarged femurs on their hind legs - muscular thighs that are used to leap away from danger. I pestered a few of our adult beetles long enough to verify that, indeed, they are excellent leapers.


Alder Flea Beetle larvae on a leaf, including
one with a fungal infection (whitish area)

Back in July, these same alder trees were covered with hundreds of small, black, caterpillar-looking larvae. But they lacked the pudgy prolegs of true caterpillars, which was enough to tell me that they were really beetle larvae, but not enough to tell me who they were. I kept watching the alder trees for more clues.

The larvae spent a several weeks eating almost every single leaf in this clump of trees, leaving mostly brown leaf skeletons blowing in the wind. In August they all crawled down out of the trees, headed uphill, and disappeared into the soil to pupate into adults.

In September, the adult beetles started showing up in the same alder trees and feeding on leftover and replacement leaves. They numbered into the dozens per smallish tree, but now that it's October the adults are starting to disappear again, back into the soil for winter. They'll emerge in early spring, mate, and lay their eggs in the soil around these trees.

For reasons unknown, these infestations only last for a few years, and the alder trees seem to suffer only minimal damage. Fungal attacks on the larval seem to play a role in checking the beetle outbreaks, and they don't spread very far because most Flee Beetle species only feed on a small handful of closely-related host plants. Some are beneficial as well, including three species of Flea Beetles that were successfully introduced into eastern Montana and South Dakota as biological control agents against leafy spurge, an invasive non-native forb.

While my Alder Flea Beetles are just a temporary nuisance, other Flea Beetle species can cause considerable damage to western crops, especially rapeseed and canola. There are also Potato Flea Beetles (potato, tomato, nightshade family), Apple Flea Beetles (primrose, grape, crabapple), Willow Flea Beetles (willows), and Cabbage Flea Beetles (wide range of cruciferous plants), among many others.

Now if I could just find a Cabbage Flea Beetle that specializes on my gastero-nemesis, cauliflower, I'd consider that one to be among the highly beneficial species.

In the Late-fall Woods

Young red osier dogwood stem, old alder trunk

Now that most of our broad-leaved trees have performed as designed, the fall forest demeanor has changed. Gone are the jittery yellow and brown autumn leaves. Now the solidarity of tree trunks stands as a more subdued scene.

The little stream that gurgled between and over their roots all summer has all but disappeared below ground, not to be seen or heard from again until spring. Along its crowded banks, the nutritious young stems of red osier dogwood stand waiting for real snow to set them apart amid the wintry grays.

The little alder trees have also dropped most of their leaves, lest the weight of a wet, early snow snap their half-rotted branches and pull them down. Shrub-like, they live fast and die young, with blue and green lichens climbing solid and hollow trunks alike, blurring the line between living and dieing.

There are reasons that, come winter, a hungry moose will browse the young dogwood stems way back. And next spring, a flighty pair of Chickadees will seek out softened alder wood to excavate for a nest to raise their brood in. Nature is always reasonable in its own ways.

Spring for a Day

Male (bottom) and female (top) alder catkins

What a difference a little sunshine makes. The lake's still frozen over and snowdrifts still abound, but the sky spills snow and rain in equal parts now. And after one warm and sunny day, it feels like spring is ready to blow in at any time.

Yesterday I heard the first Sandhill Cranes of the year, saw three micro-moths flitting about, and heard a rumor of a couple of butterflies working nearby. And the still-leafless alders were getting ready to dust the neighborhood in yellow pollen.

Alders are soft-wooded tree/shrub members of the birch family. They grow well in wet areas and, like flycatchers, there are a handful of alder species that all look very similar to me. Most alders are wind pollinated, therefore they produce early spring flowers before leafing out. And being monoecious, they have male and female flowers on the same plant, often on the same twig.

Alder flowers grow in small clusters of elongated catkins. The male catkins are starting to swell up and go to work around the lakeshore. A gentle thumping produces small puffs of pollen from a few of them already. As spring fades, and their job is done, they'll break apart and fall to the ground.

Female catkins are smaller, sturdier, and look sort of like miniature pine cones. New female catkins will be fertilized in the spring and slowly mature over the summer. By fall each brown and woody female catkin will contain 50-100 seeds. They'll persist on alder branches for a year or more.

Alders provide food for lots of native animals throughout the year. In early spring, Ruffed Grouse eat the male catkins, and bees emerging from winter rely on the early pollen to rebuild their colonies. In summer, the caterpillars of several dozen moth and butterfly species eat the leaves. Lots of bird species eat the mature seeds in fall and winter, including Redpolls, Crossbills and Pine Siskins. Deer and elk nibble at the smaller twigs year round, and beavers chew the bark off the larger stems that also double as dam-building material.

Yesterday's sunshine has slipped back into today's rain and snow mix. But the local alders are almost ready, and when the sunshine returns they'll blossom into small, yellow clouds of reproduction. Then, finally, spring will be in the air - literally.