What's eating my arum lilies?
Summer is settling in, we've had good rain, plants are recovering, birds are singing, butterflies are flitting – did I say 'butterflies'?
Butterflies and moths, as innocent as they appear, have a definite sting in the tail. To enjoy their intricate colours, their delicate dips and swings across the sun-kissed garden and their evening hovering among scented blooms, we have to live with their myriad offspring which chomp, chew and generally deface our carefully tended plants, shrubs and trees.
One of the most voracious of these is the caterpillar of the Hawk Moth, which can strip a plant of all its leaves in a matter of days. The Arum lily is one of the host plants for Hippotion celerio, commonly known as the Silver-striped Hawk Moth or Grape Vine Hawk Moth. This is an exceptionally handsome, neat looking moth with a wingspan of 76 mm and longitudinal pale brown and olive-brown stripes along the body and wings. The Arum lily is one of the host plants for this moth. I followed one caterpillar's development from the beginning of June until the middle of July 2011 during which time it ate its way through three bags of young arum lilies before it was ready to pupate.
A week or so later the teeny, cute little green caterpillar was a staunch 7 or 8 centimetres long, had turned brown and descended to the base of the plant where once again it blended perfectly with its surroundings. Here it spent the day in hiding, creeping up during the night to continue its depredations.
Once it had eaten its fill, fattened and slightly swollen, it descended to the ground and lay sluggishly on the debris for a day or two, no longer ascending for its nightly feed. It then made a rudimentary shelter in a hollow between the stalks with a few strands of silk at the base of the plant to await metamorphosis.
A couple of weeks later I carefully removed it from its nest to take these photos, then replaced it to continue its journey. Unfortunately I waited too long to witness its emergence and by the time I went to check on it, it had already flown away.
I hope in the future to photograph one of the moths of this species to add to the blog so as to complete the cycle. In the meantime you can go here https://www.google.co.za/search?q=hippotion+celerio+moth&es_sm=93&tbm=isch&tbo=u&source=univ&sa=X&ei=toNbU9aTGIey7AbtsIGgDA&ved=0CDkQsAQ&biw=1160&bih=563 to see pictures of the adult moth.
The impact on my Arums
The damage to the arum lilies was the loss of their leaves which admittedly hindered their growth but they recover. To save your Arums, visit them regularly and check for eaten leaves and along the stems, where you will find the culprits.
I have also included a (rather poor) picture of two eaten leaves so you have a better idea of what to look for when searching your plants to find the caterpillars. Notice that the eaten edges of the leaf on the left are brownish and dried. This is old damage and the caterpillar has probably moved on. The edges of the leaf on the right are still green. This is where the culprit has been eating during the previous night. Look under leaves with fresh, green edges like this and you will most likely find the caterpillar.
Before you go on the rampage, consider the results of your actions
So now it's up to you. You may decide to pick off and destroy both the eggs and the caterpillars, but bear the results of this action in mind: birds will find less food in your garden and may leave to find food elsewhere, night blooming flowers will not be pollinated and bats will be deprived of a protein packed 'snack on the wing'.
It's all about balance. Three seasons back, in my innocence and to my shame, I eradicated every hawk moth egg and caterpillar I came across, so decimating the population of this species of Hawk Moth in my garden that I found no caterpillars last season and only five this season, of which three disappeared before reaching maturity - presumably eaten by birds. This season I sacrificed a few of my arum lilies to protect next season's generation of hawk moths and I have learnt to live and let live. It's scary how long it takes for a species to renew itself after the damage is done!