The Box Tree Moth originates in south-east Asia and is now well established in the UK. Drinking tea with a friend she spotted and identified this one on a window pane. 

 The caterpillar feeds on the leaves of Box Trees causing considerable damage. Box (Buxus sempervirens) is native to the UK but in a few sites only, notably Box Hill in Surrey. I wonder why a plant that is native and hardy is so limited in its spread?

 However it is widely grown as an ornamental and therein lies the problem. Box Tree Moth undoubtedly arrived via the horticultural trade on imported stock. 

 We have a similar issue with Ash dieback which is caused by a fungus (also of Asian origins) and well on the way to decimating the UK's Ash trees. Ash is one of our most common trees; clearly there is no difficulty growing it here. None the less it became more "economic" to grow stock abroad then import it. This coincided with the arrival of ash dieback in eastern Europe on imports from Asia.

 Pests and pathogens may extend from their native range anyway but global trade hastens that process considerably. In fact it's a theme of this diary that introduced species increase biodiversity in ways that are frequently benign. On the other hand introductions can be problematic. A species -be it flora or fauna- may be subject to checks and balances in its native habitat which don't apply in a different ecosystem.

 Nature can and does assimilate change. There is so much genetic variation in this country's Ash trees for example that dieback may meet its limits at some point. As for economics, well that's another story...