The boxwood butterfly (Cydalima perspectalis) is native to Southeast Asia and was unknown in Europe until recently.
It was discovered in Germany in 2007, presumably imported with products from China, and has spread rapidly since then.
It is without a doubt a very invasive species and as the name suggests, the box hedge plant is the food plant for its caterpillars.
Box is widely used as a hedge in gardens, and has been for a long time, making it a well-established plant almost anywhere.
The boxwood moth.
Simultaneously with the discovery in Germany, it was also registered in Kent either in imported hedge plants or perhaps as a migrant who had flown across the English Channel.
It established itself across the country very quickly, and since it has two or three generations a year, the number soon increased.
It was first registered in a moth trap in Bonchurch on the Isle of Wight in 2013.
These traps use a bright light to attract moths, which then end up in a part of the trap that is difficult for them to escape.
The trapper then records and photographs the catch, and once this is complete the moths are released back to where they were caught.
There are a number of people interested in this all over the island and an annual report is made by the Island Recorder which then forwards it to Butterfly Conservation.
The next record on the Isle of Wight wasn’t until 2016 when two were posted, 123 by 2020 and this year, 2021, multiples fall into the trap.
It should be noted that there will be far more moths on the island than are actually seen and registered as so few people search, but more and more gardeners are reporting damage to their box hedges and this will only increase.
The caterpillars glue several leaves together and then place a white silk net around them, giving themselves a safe place to live.
These nets are very obvious and are usually the first sign of the moth, but once they start eating the box leaves it is likely too late for the plant and it will turn brown and die.
It seems that very little can be done about this infestation, but research continues.
The moth has a wingspan between 38-42 mm and has two different color forms; the normal white winged form and the black (melanic) form tinted with blue and purple.
Both are easy to spot. There is little effective control if your box bushes are severely attacked, so this moth is likely to stay here.
Many gardeners have to use alternative evergreen bushes for hedging, which are not affected by boxwood moth caterpillars or boxwood rot.
Click to read more about box rot in this week’s garden column