Fabulous Pheromones

For years now, we have been seeing the larvae of the Vapourer moth on the Tamarix shrub that we have in our front garden. However, my only sighting of the adult moth of this species was a very distant one in Derbyshire 2017. I had never seen the moths of this species in the garden.

Vapourer (Orgyia antiqua) (larva) - our garden

This species of moth is one of the few in UK that feature flightless females. I therefore hatched a plan to harvest three of the larvae and rear them indoors in the hope that, by the law of averages, I'd get to see one of each sex. The larvae are known to have very irritant hairs and so I carefully cut three stems with larvae attached, and with what I hoped would be a sufficient amount of food on, and placed them in a milk bottle full of water (with the neck carefully sealed to prevent them from drowning). This was then placed in a rearing cage.

I regret that I did not have the presence of mind to record the date of this event and the dates on which the three larvae pupated, but it seemed that it all happened over just a couple of weeks. The pupae were contained in cocoons of silk attached to a tamarix twig or, in the case of one, to the netting in the corner of the cage.

Then one warm sunny day, while I was sitting in my study, I found what I first thought was a small orange butterfly (skipper sp. came to mind) rapidly flitting around me. I grabbed a net and, to my surprise, found that it was a male Vapourer.

Vapourer (Orgyia antiqua) (male) -from my study

This discovery caused me to quickly examine the breeding cage in case I'd left the cage open or it had been damaged. Sighting no damage, but an emerged female Vapourer in the cage brought the amazing realisation that this male had detected the pheromones being emitted by the female through the fine mesh of the cage then through my study and the door into the kitchen, and then through the kitchen and kitchen door to the outside and to wherever this male happened to be at the time! Here's the female, still attached to the pupal cocoon which is where, usually, she'll spend the rest of her short life.

Vapourer (Orgyia antiqua) (female on cocoon) -from my study

I quickly put the twig that she was on into a bottle and out into the garden, where I placed the bottle on a bench. Within seconds, rather than minutes, there were four more male Vapourer moths attracted to her and all trying to mate with her. Photography-wise I was not at all prepared for this, and my photos are rubbish but maybe you'll understand the situation better anyway.

This first one briefly settled on the bench beside the bottle before joining the action.To the best of my knowledge, Vapourers usually rest with their wings folded backwards so that the forewings touch or slightly overlap at the rear and the spots are close together - as in the image above. I am wondering if this one had its wings spread due to a state of excitement?!

Vapourer (Orgyia antiqua) (male) - our garden

This next shot depicts an arriving male, with two already in attendance - the female is not visible and is behind the cocoon on the twig.

Vapourer (Orgyia antiqua) (males) - our garden

The next shot depicts at least three males attempting to mate with the female.

Vapourer (Orgyia antiqua) (males + female) - our garden

It seems that, as soon as she has attracted a mate, she stops emitting pheromones and, after mating was finished, the males quickly departed.

She then started ovipositing on the cocoon - which is the norm for this species. The eggs are white when first laid.

Vapourer (Orgyia antiqua) (ova) - our garden

When ovipositing is finished, the female remains in place on the cocoon and by the ova. In this case, within 24 hours, the female had shrivelled to maybe a third of her size and was apparently dead.

The twig with the cocoon and its ova are now taped to a sturdy branch on the Tamarix in the garden.

Just two days later, the next one to emerge was, again, a female. This was the one with the cocoon in the corner of the cage, rather than on a Tamarix twig. The cage was placed outside on the bench and almost immediately attacted a single male. I do not know if this lack of choice of suitors was due to the dull cooler weather or whether her pheromones weren't so attractive.

Vapourer (Orgyia antiqua) (male + female) - our garden

Two days later, I noticed that the female had dropped off the cocoon and was on the floor of the cage. She hadn't shrivelled up like the previous one so I thought I'd get some photos.

Vapourer (Orgyia antiqua) (female) - from the cage

I'd just taken that shot above when I noticed her legs starting to move. I gently righted her and she started to crawl across the bit of green card that I was using as a background. This next shot, and that above, clearly show the vestigial wings of the female Vapourer.

Vapourer (Orgyia antiqua) (female) - from the cage

I then carefully placed her on the Tamarix outside. I don't suspect that she had much of a life ahead of her, however.

The eggs in the cage had taken on a more subdued colour and showed some surface detail.

Vapourer (Orgyia antiqua) (ova) - in the cage

The third Vapourer emerged a few days later, again on a dull day, and again a female! This one also attracted just one male. After ovipositing she shrivelled up to almost nothing and was clearly dead. 

All the ova are now out on the Tamarix and I await next year with interest to see if I have a bumper crop of Vapourer larvae!

FOOTNOTE:

This little 'experiment' was prompted by me never having seen an adult Vapourer moth in our garden. Just over a week after that last emergence of a female, I found an adult male sitting on the garden fence - perhaps the word had got out that there were females about!

Vapourer (Orgyia antiqua) (male) - garden on 11th August, 2021

That's it for now. I hope that you have found this interesting. I wonder what I will come up with next!

Look after Nature and Nature will look after you.