Dear Readers, there have been a number of stories in the press this week about ‘Dangerous Biting Insects Spotted in UK for First Time in 18 Years’, and the culprit is pictured above – the Plane Lace Bug (or Sycamore Lace Bug if you live in North America). The big worry is actually not about the insects ‘biting’ (they are only 4 mm long, and there have been very occasional reports of them biting and causing a ‘mild rash’). The real problem is that London has many, many plane trees (the London Plane is probably ‘the’ London tree – there are estimated to be over 100,000 in the capital). The Plane Lace Bug comes originally from North America, but it is now widespread in mainland Europe, where it causes extensive damage to plane trees (you can read about what’s happening in Brussels here).

Like all true bugs, Plane Lace Bug has sharp, piercing mouth parts, and feeds on sap. Both adults and nymphs cluster on the underside of leaves and feed from there, nicely hidden from birds and other predators.

The leaves that are infested turn yellow, particularly along the veins, and may fall early. Repeated infestations may weaken the tree and eventually cause it to die. Infestations are also much more likely to occur on trees that are already stressed by heat, drought, shallow soil and the other problems that street trees face. Occasionally the infestation weakens the trees enough to allow damaging fungi to take hold, which then kill the tree. You can see why a Plane Lace Bug infestation could be a serious problem.

In 2006, Plane Lace Bugs were spotted at a nursery in Bedfordshire, imported with plane trees from France and Italy. Fortunately this particular infestation was treated, but it was found that there were already Plane Lace Bugs on the mature London Plane trees close to the nursery site, and the decision was made that the insect was in effect already here, but wasn’t causing serious damage. For this reason, it was decided that no statutory action was required.

The Forestry Commission has now confirmed (September 2024) that Plane Lace Bugs have been found on plane trees in central London. The Woodland Trust sent out volunteers from the  Observatree programme to look for signs of Plane Lace Bug damage – this is a specially-trained group which will look for specific pests and diseases if there is an alert. If you see someone looking up at a plane tree with a pair of binoculars, it’s probably someone from Observatree! If you see something suspicious you can report a suspected sighting on the Tree Alert site here.

An example of the leaf damage is below:

So, I imagine that until we have better surveillance we won’t really know how extensive the Lace Plane Bug problem is, and how much of a danger the insects present. In mainland Europe they can gather in large swarms, entering homes and generally making a nuisance of themselves, but there’s no sign of that in the UK (yet). In the meantime, if  you live in London, keep an eye on your trees.

But what to do if there is an infestation? The use of insecticide on mature plane trees would be costly, inefficient  and extremely damaging to the rest of the ecosystem. DEFRA (the Department for Environmental, Rural and Agricultural Affairs) suggest other remedies such as ‘hosing down’, ‘soapy water’ and the use of biocontrols such assassin bugs, spiders and mites where the infestation is spotted early. And that is probably the key. Maybe we should all be assigned a plane tree to keep an eye on. I will certainly be taking the time to check out the beautiful trees along East Finchley High Street.