Lackey Moth caterpillars (Malacosoma neustria) were present in great numbers along the Pembrokeshire coast both north and south of St Davids last weekend. This species belongs to a family of tent caterpillars, so called because of the distinctive silk ‘tents’ that the newly emerged caterpillars build. These tents are positioned to intercept the early morning sun so that the caterpillars contained within can elevate their body temperature as quickly as possible during early spring. The tents are constructed from distinct layers of silk separated by air gaps to form separate compartments, the temperatures of which can vary widely. By moving between these compartments the caterpillars can regulate their body temperatures as necessary throughout the day. The sections of the coast path that we walked were lined with huge quantities of these tents, many of them still containing masses of newly emerged caterpillars.
As Lackey Moth caterpillars develop they go through several growth stages, shedding their exoskeleton during each transformation. Their initial form is shown in the photo above, while their final and more colourful form is shown in the photo at the top of this post. Many of the exoskeletons were still hanging around the tents as shown in the left of the photo below.
As you can probably imagine, this quantity of caterpillars in one place can have a massive impact on the surrounding vegetation. New tent locations were easy to spot as typically the surrounding bushes had been stripped completely bare of all their leaves. This probably explains why we saw several of the caterpillars travelling across the path at various points, no doubt in search of fresh food sources. The photos below show the results of their huge appetite.
I have never seen these caterpillars or their tents before so I’m not sure if we were particularly lucky this time around or if they have had a bumper year. Wikipedia mentions that these species often exhibit a boom or bust breeding mentality so it is quite likely that this year has seen a population explosion. I’d be interested to hear from anyone else who has seen these creatures on their travels.