Webbing in the crotch of branches in spring is a sign of Eastern tent caterpillars. Photo: J. Hahn U of MN

If you notice a silken web on your deciduous trees and shrubs this spring, it's most likely Eastern tent caterpillar. Eastern tent caterpillars are fairly common in spring and maintain a steady presence year after year. Host trees include ash, birch, fruit and nut trees, oak, redbud, and popular. Another common tent caterpillar active in the spring is forest tent caterpillar, commonly found in northern and central Minnesota.

Eastern tent caterpillars are easy to identify because it constructs silken webs in the fork of branches as soon as the young larvae hatch. The caterpillars feed outside of the tents on leaves during the day (as long as the weather is nice) and return to the webbing at the end of the day and during rainy weather for protection.

The caterpillars are bluish black with yellow and a white stripe running the length of the top of its body. They are also mostly smooth except for a series of hairs sticking out along the side of their bodies. They are two inches when fully grown.

Forest tent caterpillars, commonly called armyworms, are blue and black with distinctive footprint or keyhole shaped white spots on their backs. They are mostly smooth except for hairs that stick out along the sides of their body. They grow to be two inches long when fully grown. They do not make conspicuous webs on trees.

A healthy tree can survive a heavy defoliation from tent caterpillars. Shown mature Eastern tent caterpillars. Photo: Terry Price Georgia Forestry Commission

Base your decision to treat tent caterpillars on several criteria. First, consider what percentage of leaves has been eaten. If only a few branches are affected, the tree can tolerate that damage. Leaf feeding tends to be more a cosmetic problem and not one that threatens the health of the tree. Even if defoliation is severe, healthy, well-established trees can withstand this feeding in a given year. However, young trees are less tolerant and should be protected. Unhealthy, stressed trees should also be protected from severe defoliation.

Second, consider the size of the insect. Ideally these insects should be treated when they are 1/2 their full-grown size or smaller, i.e. about one inch in size. The larger they are, the closer they are to being done feeding. If they are close to two inches long, by the time you see them, it is not worth treating them.

If treatment is needed, consider using products that have a low impact on the environment, such as Bacillus thuringiensis, spinosad, and insecticidal soap. Mechanical means can be used to control tent caterpillars too. Remove any egg masses that you see on the tree before they hatch. Nests can be cut out of the trees and disposed of if caught early.

Now if you witness webbing with insect presence in late summer into fall that pest is the fall webworm.

For More Information:

Tent Caterpillars from U of MN Extension

The silver and green leaves will pop when placed in a shady location.

Looking for a plant for a shady spot in your yard? Look no further than Brunnera macrophylla 'Jack Frost'. 'Jack Frost' works well in deep shade to partial shade conditions and prefers wet feet pretty consistently. First introduced in 2000, this variety has been growing in popularity. The striking bi-color foliage of green and silver stays strong even after the plant is done blooming its dainty blue flowers in mid-May.

It also shows resistance to deer and rabbits due to the rough furry leaf texture once fully formed. A mature plant will grow to 12 to 15 inches in height and 24 inches in width.

Pair 'Jack Frost' with Pulmonaria, commonly called lungwort and blooms at the same time, hostas, try blue leaf 'Krossa Regal', and heucherella.

If this plant couldn't get any better, it is hardy to zone 3. But it's not perfect as it may be affected by mildew and rusts if the leaves are wet too often.