The perilous life of a caterpillar
Caroline Ware   Forum Trustee
July 2017

At this time of year even the simplest of garden tasks need to take account of insect habitats and food. Before starting work there’s a necessary check for clues of habitation such as rolled-up leaves with intricately spun and knitted threads that may be cradling moth or butterfly larvae,

A rolled up nettle leaf……
Nest of the Common Carder bumble bee (Bombus pascuorum)

If I forget to carry out this risk assessment, I may accidentally remove someone’s lodging or food plant. There was a near miss a couple of weeks ago.

I was rearranging a motley collection of potted sempervivums with their self-sown pot-sharers and found a hapless yellow, green and black caterpillar that had dropped on to the soil in one of the pots. Thinking it was a caterpillar of a Large White butterfly because garlic mustard (Alliaria petiolata) was growing next to the pots, I put the pot and caterpillar within reach of the garlic mustard leaves, but the caterpillar wasn’t having any of that. 

Next guess was a Mullein moth larva and although I don’t have any Mullein (Verbascum) at present I’d heard that the moth larvae also feed on buddleia which was growing nearby. I placed a buddleia leaf in the path of the caterpillar but it reared up and turned away as if in disgust.

Purple toadflax (Linaria purpurea)  is self-sown in and around my flower pots and in the cracks of the brick path and, although I had noticed that the leaves had been stripped off several  plants, I wasn’t concerned as it hadn’t  detracted from their charm. But, through fresh eyes, it had to be the host plant for this beautiful caterpillar.

<< Blog entry >>
...may be harbouring the Nettle tap caterpillar (Anthophila fabriciana)

Or, a flower or grass stalk supporting a well camouflaged cocoon ...
... a Six-spot Burnet moth cocoon (Zygaena filipendulae) on stem of false oat-grass (Arrhenatherum elatius).

Or, more vulnerable at ground level, a small bundle of carefully carded moss and dried leaves may be a bumble bee nest.
Common toadflax (Linaria vulgaris)

On closer inspection, this caterpillar had distinctive markings with stripes running length-ways rather than bands across the body as with the Mullein moth.  A search through my moth books led me to the Toadflax Brocade moth (Calophasia lunula).

Purple toadflax (Linaria purpurea), native to Italy and naturalised in many parts of the UK.

Closely related to our native common toadflax (Linaria vulgaris) below
The caterpillar reaching out to eat from the tip of the toadflax leaf

It was rapidly growing - from approximately 3 cm on 29th June it was 3.5 cm 3 days later and about 4 cm by the 5th July.

On Thursday morning I failed to find it – but there it was when I returned in the evening. Finally on the 8th July, it was no longer on its patch. Either it has been predated or crawled away to pupate. At over 4 cm long and in the final instar stage, the latter is likely. I searched the immediate area for signs of a chrysalis, but found only a smaller relative, discovered two days previously. This last caterpillar was also growing healthily and was over 3 cm. A couple of days later it too had disappeared hopefully to pupate.

Caterpillar of the Toadflax brocade moth (Calophasia lunula)

The Toadflax Brocade was first noted in Britain in 1939 on the south coast at Shoreham in Sussex, and later the first larva was recorded in Dungeness, Kent in 1952, followed by sightings in other areas of the south and south-east coast near shingle beaches and other sparsely vegetated habitats. Within the last 15 years its territory has expanded inland and it’s been recorded in north and east London. However it is still considered a relatively rare species and I’ve been watching over it protectively.

Following a week of caterpillar watching I nearly lost it again while pruning back some elder.  I didn’t consider where I was throwing the elder branches and knocked the purple toadflax on which I had last seen the caterpillar. I searched for the caterpillar, and finally found it the next day, and 2 tiny relatives I’d previously missed.

A week after first spotting it, the caterpillar was 3 cm long and in residence amongst self-sown toadflax in a tall Spanish pot, while its remaining tiny relative was just half a centimetre long and in a more vulnerable position on the ground. It wasn’t growing as quickly as the larger larva.

Well camouflaged but vulnerable – its tiny relative (centre) close to the ground

The caterpillars are well camouflaged and sometimes impossible to find during my early morning check. In the evening I usually find it again on a different plant nearby. Its camouflage would be even more effective amongst native yellow toadflax (Linaria vulgaris) its primary food plant.

The caterpillar occasionally gets irritated by a hoverfly circling around on nearby plants, or ants investigating leaves for honeydew dropped from aphids on overhanging willow – this ‘irritation’ I interpret from the manner in which it rears its head with the same distain it showed for the buddleia leaf.

The caterpillar feeds on leaves from top of the plant working its way down the stem. Initially the young caterpillar was found resting and eating along the leaf as in the above image. As it grew in size it travelled up and down the stem reaching out for the tip of the leaf and munching it from the tip to the inside. After eating a leaf or two it reverses and ‘rests’ near the top of the plant but I’ve yet to observe whether it reverses or turns around to travel to the top.

The Toadflax Brocade moth sometimes has two generations and I’ll be watching out for the second generation in August or September.

In the meantime, I’m tiptoeing around my occasional garden duties. It’s a perilous life for a caterpillar with risks of predation from birds, spiders and wasps not to mention disturbance from careless humans.

So now I sit guilt-free watching and enjoying the summer display of munchers, sap-suckers and pollinators and, with the Big Butterfly Count  around the corner I’ll be listing all butterfly visitors in addition to moth larvae.