The Satin Moth (Leucoma salicis) is a non-native insect that was introduced to North America from Europe in the early 1920s. The satin moth population in the Calgary area has been generally non-problematic. This season a combination of environmental events have permitted Satin Moth populations to expand and become more noticeable. The caterpillar feeds primarily on the leaves of poplar species. They have also been known to feed on willow and oak trees.
Satin Moths can completely strip and defoliate large mature trees of all their leaves. They produce two occurrences of leaf eating caterpillars in a season and therefore can defoliate a tree twice. Mature healthy trees normally have enough resources stored to be able to recover from this type of damage. Repeated, severe defoliation over a few seasons can result in tree mortality. Rolled leaves containing pupae and silk webbing on stems and branches are signs of the Satin Moth pupae.
The mature Satin Moth caterpillars grow to be 3.5 to 4.5 cm long, and are pale to medium grey-brown, with a darker head and back. Their backs are black with a central row of white or light yellow markings. They can be confused with the tent caterpillar which has a white strip down its back bordered by two blue lines. The adult moths have pure white wings with a satin-like lustre. They have a wingspan ranging from 3.5 to 5.0 cm and can be distinguished from other local white species by narrow alternating black and white bands on their legs.
Residents can help manage Satin Moth on trees on their property. How you manage them is closely related to the insect’s lifecycle. Satin Moth overwinters as a caterpillar in leaf litter, in the lower branches, and in the furrows of the bark of the tree. The Satin Moth caterpillars will begin their climb back up into the tree in May. Applying “sticky bands” is still an option for homeowners as they are able to more closely monitor Satin Moth activity and the effectiveness of the band.
The greenish egg masses concentrated on the lower tree trunk can be scraped off with a dull blade and destroyed before they hatch. High pressure washing does appear to be an effective management technique. These services can be secured through local tree care companies. These eggs masses appear around mid-July. Again, “sticky bands” can be applied to the tree trunk during leaf out in May and again in July to catch newly hatched caterpillars as they disperse into the canopy of the tree. These bands can be found at local garden centers and should be reapplied once they are saturated with the caterpillars.