Dense colonies of the scale insect result in yellowing, shedding of leaves, dieback and occasional tree death.
Compared to other invasive insects, it has spread slowly across the north-eastern U.S. and has reached Georgia in the south, as well as Michigan, Kentucky and Tennessee further west.
The scale cover of the second instar female is elongated, around 1.5 mm long and has a yellowish-brown, orange-brown or reddish-brown colour.
The eggs hatch in spring and the crawlers migrate to new needles of the same host plant, or may be carried over longer distances by the wind or by birds.
[10] Some research has been directed at trying to understand the differences between North America and Japan in the population dynamics of F. externa and E.