Having the privilege to watch the amazing life cycle of the Vapourer moth has been fascinating! 

It was about a month ago, me and Theodore were looking around our back garden, trying to find some interesting insects to photograph and identify. We were looking on this shrub for spiders when I noticed it was COVERED in these odd looking caterpillars.

I had never seen anything like them, with colours of dark grey, red and yellow, covered in bristles and tufts of hair. I decided to do some research on these crazy caterpillars, knowing that they will be my garden friends for the future months.

With the help of some great people, in one of my favourite Facebook groups, Caterpillars UK, I identified them as Vapourer moth caterpillars.

Let me give you some background information about these critters. The Vapourer moth is also known as the Rusty Tussock  moth, Orgyia antiqua. They are a common resident in Britain and are usually found in shrubbery around gardens, open woodland and hedgerows. 

Now for the life cycle, which is the main information I want to share with you today. I will list it, in the order of the stages I have observed. I named the 2 of them, Ru and Paul.

Caterpillar (larvae). At this stage, they are a mixture of dark grey, red and yellow colourings, growing 30–40mm, the females tend to be larger than males. They have four clumps of yellow tussock hairs along their back and hair pencils protrude from the front, sides and back. 

They have defensive glands on their back, which they use to wipe their setae (a stiff hair or bristle) over to charge them with toxins. You can watch a video of this on my Instagram here.

Cocoon (pupa). After having eaten their way through their common food of deciduous tree and shrub leaves, they begin to create a silk cocoon. In the ones that I observed, it took them about 24 hours to complete it.

I noticed that as she was working on her cocoon, she was shedding her larval hair (setae) and incorporating them into the cocoon. Like in their larval stage, these hairs are irritating to the touch, so is a good defense against predators while developing over the next 8-15 days. Ru stayed in her cocoon for 14 days. 

As seen above, the silk cocoon itself is translucent, allowing me to observe the changes of the pupa. It is soft to the touch and was built at the top of a twig, whereas Paul decided to build his on the underside of a leaf. 

If you notice in the bottom left corner, it is what appears to be the caterpillars first layer of skin that has been shedded along with any remaining setae. The larvae then stays inside it’s exoskeleton, contained by the silk  cocoon. This ‘shell’ is called the puparium. 

Adult moth (imago). Once fully developed, the adult must then break free from the cocoon. There are a few ways that different species use to do this. From my observations and the knowledge that the cocoon is quite soft, I am going to speculate that they build the cocoon with a point of weakness that can be easily teared opened from the inside or an exit hole at the top part allowing a one way passage through to the outside world. 

This is where it becomes very interesting! The adult males and females look drastically different and behave differently too, this is called sexual dimorphism.

Females are actually flightless. They have vestigial wings and a large abdomen with short antennea. They are a light grey–brown colour and look very plain in comparison to their larval state. 

Vestigiality is a process of evolution where an organism retains a genetic structure or behaviour pattern that no longer fulfills the original purpose. An example of this is the human appendix.

Female Vapourer moth, close up of vestigial wings.

When they finally emerge,  females spend the rest of their short lives clinging to their cocoon. They begin to release a pheromone that will attract a male to them, to mate and ensure a next generation. You can see a video of this, on my Instagram, here.

Males have orange to red-brown wings, with each wing having a white comma shaped spot. They have a wing span of 35-38mm and short antennea. 

Often flying during the day, searching for females, this means they are diurnal. Flying high up and most commonly seen in the early to late afternoon of sunny autumn days.

Paul also turned out to be a female. Paul is now Paula! 

Eggs. After mating, the females will lay their eggs straight away. Usually around 100-200, covering the outside of the empty cocoon. They have a creamy-brown colour, are rounded and have a ‘target’ design on the flattened top.

Sadly, the adults do not live for very long after mating. The eggs will then overwinter and hatch around early spring time, producing a new generation of Vapourer moths. So, the cycle continues!

I hope you enjoyed learning about this amazing moth along with me! Thankyou to Ru and Paula for allowing me to observe them and good luck to their babies for next year! 

Thanks for reading!