Dear Readers, when I was wandering through Cherry Tree Wood here in East Finchley a few weeks ago, I was fascinated to see that some of the trees had these ghostly nets in them. The silk is similar to that of spiders, but because it is protective rather than used to catch insects, it’s opaque and surprisingly strong. In the midst of the tent above I could see frass, the black droppings of caterpillars. Some little critters had obviously been having a lovely time eating the new leaves. It didn’t take me long to find the culprits – the caterpillars of the bird-cherry ermine moth (Yponomeuta yvonemella).
These caterpillars will be gone by the end of June, giving the tree plenty of time to recover. After all, compared with some webs, this was a mild one.
There is definitely safety in numbers – when the caterpillars all emerge at the same time it makes it less likely that an individual larva will be eaten. Furthermore, even the most diligent blue tit won’t want to foul her feathers with too much of that sticky stuff.
The caterpillars will pupate briefly, and then this rather elegant moth emerges. You can see how its resemblance to a winter-coated stoat gave it its name – just think of the white, black-spotted fur that lines the ceremonial robes of mayors and royalty. I always think that every black spot was once the tip of the tail of a small predator, and count how many died to make each outfit, but maybe that’s just me.
There are several other species of ermine moth in the UK, the commonest being the orchard ermine (which feeds mainly on hawthorn and blackthorn) and the spindle ermine that munches through (predictably) spindle. None of them are any threat to the plant, and their populations will naturally fluctuate according to the weather and to the availability of food and the number of predators.
As I was perusing the ermines and getting a few photographs, I was accosted by some young women who were anxious for their children.
‘Are these those dangerous caterpillars that I heard about on the news?’ they asked.
I was able to reassure them. The ‘dangerous caterpillars’ are the young of the oak processionary moth, a European mainland native that has been imported (just like ash dieback) on young trees for landscaping. These insects have been spotted in several places in West London, and they are considered a problem because they are ‘urticareous’ – that is, their hairs are likely to cause dermatitis and even asthma if inhaled. The clue to their behaviour is in the name: the processionary moth caterpillars follow one another around en masse. Their nests tend to be on the branches and trunks of oak trees, never among the leaves as with the ermine moths. You need to be in close contact with the caterpillars for them to cause any harm. The Forestry Commission are treating the outbreaks that they know about (probably with huge doses of biocides) and if you spot any actual Oak Processionary Moth caterpillars you can report it here.
I do wonder, however, how many perfectly harmless caterpillars have been killed as a result of all the quasi-hysterical news reporting of the oak processionary moth. The story has all the ingredients for a media storm: invaders from overseas: a danger to children: an attack on that very bastion of Englishness, the oak tree. Many people have a fear of insects, and most of us have a fear of insects in very large numbers. I suspect that some people might have seen a caterpillar net in their garden and doused it with insecticide without stopping to identify it. Which would be a real shame, because some extremely rare species superficially resemble the oak processionary moth.
One of the most endangered is the Small Eggar (Eriogaster lanestris). This species lives in hawthorn, blackthorn and birch, and the caterpillars create a nest about the size of a small football. The larvae are attuned to one another and it’s believed that they communicate about where the best feeding opportunities are, before leaving to forage en masse. They have been under extreme pressure due to the loss of habitat in the countryside, and so are more likely to come into contact with humans. What a shame it would be to lose this creature because of mistaken identity.Another possible victim of over-enthusiastic caterpillar killing is the Nationally Scarce lackey moth (Malacosoma neustris), which has some of the most appealing larvae of all lepidoptera, at least to me – I spent a lot of time playing with these creatures as a child, and although they too could set off dermatitis in those who are susceptible, I never had any ill effects. These caterpillars also live in nets and their preferred foodplants include oak. cherry. plum, apple, willow and hornbeam. You can see how these chaps, spotted in an oak tree, could be doomed from the start, although their caterpillars look very different from those of the oak processionary moth, and their behaviour is quite different.
The eggs of the lackey moth look as if they’re made of ivory, and are always laid around a twig. I wonder if the mother gets dizzy laying them?In fact, to our human eyes, the adult moth is the least beautiful stage of the lackey moth’s life, although it is still a very handsome creature. So it seems to me that the ability to identify an oak tree, and to tell the difference between a lackey moth caterpillar with its cartoon-like blue face and the ultra-furry oak processionary moth caterpillar are what’s required to prevent the accidental extermination of rare moths who are already under extreme pressure. And also, it helps if, having learned these things, we communicate them to our children. No one wants their little ones to be bitten or stung or hurt in any way, but the best way of keeping them safe is to help them to understand what’s safe and what’s not. Children are naturally curious, and when they’re outdoors they will probably fall off of logs, get stung by wasps and come home covered in bruises and dirty. It’s hard, I know, but we cannot protect those that we love from things that hurt them and nor should we. How can we learn resilience without a little adversity? And besides, exploring the outside world and discovering things for ourselves is so much fun that it will bring us joy for a lifetime.
Photo Two by By David Short from Windsor, UK – Bird cherry ermine (rp), CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=63856375
Photo Three by By Kleuske – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=19940595
Photo Four by By User:MarkusHagenlocher – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=2151016
Photo Five by By Hans Gasperl [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], from Wikimedia Commons
Photo Six by [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)], from Wikimedia Commons
Photo Seven by By H. Krisp – Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=19806408
Photo Eight by By José Manuel Benito Álvarez [CC BY-SA 2.5 es (https://creativecommons.org/licenses/by-sa/2.5/es/deed.en)], via Wikimedia Commons
Photo Nine by By Ben Sale from UK ( The Lackey (Malacosoma neustria)) [CC BY 2.0 (https://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons