Ruud Kleinpaste
Ruud Kleinpaste on the dastardly garden-decimating deeds of a certain looper caterpillar
Get to know green looper caterpillars
just when you thought it was safe to become a little more relaxed on the pest-control front in your garden, the green looper starts its final generation. And as seems to be customary with this species, the numbers of moths, pupae and caterpillars happen to be at their peak too at this time of the year, whether you’re in Northland or Canterbury.
I’m sure most folk are familiar with this mean, green eating machine. The caterpillar is the stage that does the damage to leaves, developing fruit and buds. It can grow to 40mm in length and despite its bright green colour can be difficult to detect as it hides on the underside of leaves during the day.
When these caterpillars are small, they’re absolute masters at camouflage, pressing themselves against leaves. Their main feeding activities take place under the cover of darkness, when they set to work munching holes in leaves and other plant material. On pot plants kept inside, the appearance of frass (caterpillar poo pellets) in increasing sizes gives the game away.
The truly remarkable amount of this excrement also gives you some idea about the voraciousness with which these larvae devour your precious plants. Grow coleus, pelargoniums or geraniums, cabbages, chrysanthemums or dahlias, and the leaves will disappear before your eyes. The green looper will also gnaw on tomatoes, beans and pip fruit.
I used to keep these caterpillars in captivity so I could observe their curious method of locomotion and watch the incredible way some parasitoid wasps destroy their bodies. Without going into the details of entomological classification, it must be pointed out that the green looper is actually not a real “looper” at all, but actually a semi-looper, which adapted a walking style on two widely spaced groups of legs.
At the front, just behind the head, are three pairs of small, segmented legs ending in tiny claws that help to grab onto plant material. Then, towards the end of the muscular and quite powerful body, a few more pairs of nonarticulated fleshy lobes act as the hind legs.
This set-up is perfect for creating the looping motion when the caterpillar is moving about on the plant. It stretches the front legs out to where it wants to go, grabs onto the plant material, then drags the hind legs up, while the body forms an impressive loop, not unlike the Greek letter omega (Ω).
Once you know what you’re looking for, you’ll be able to find these cute green packages of protein no problem. I catch them as fodder for my selection of captive predatory invertebrates; the giant centipedes love these caterpillars, and so do the ground beetles, mantids and tunnel web spiders in my garage.
Out there in “the Nature” (as one of my friends calls the big, bad world of bug eat bug), there’s a tiny parasitoid wasp that punches well above its weight. This minute wasplet uses a clever polyembryonic trick to use the whole body of a full-grown green looper caterpillar as food for her many babies. All she does is lay a single microscopic egg inside a developing caterpillar. This egg then divides into two eggs, and the two eggs into four, eight, 16 – you get the picture. Despite all this, the caterpillar keeps on eating. In fact, even when all the eggs hatch into protein-obsessed endoparasitic carnivores, the caterpillar keeps on doing what it does best: creating holes in leaves and fruit. Imagine, with something like 1200 little parasites on board!
It’s in the parasitoids’ best interests to keep their host alive for as long as possible, as it’s surely no fun crawling around in decaying caterpillar flesh with 1199 closelyrelated siblings all competing for the same resources. Indeed, in the first phase of their development, the wasp babies feast only on nonessential substances (such as fluids and fatty tissues). It’s only when the caterpillar starts to spin its cocoon, in preparation for metamorphosis into a chrysalis, that the larval wasp parasitoids will strike and finish the job.
And that’s what you’re likely to find at this time of the year: a half-finished cocoon with a massively swollen caterpillar body inside it, full of hundreds and hundreds of small wasp pupae, bulging out of the skin of that once proud, mean, green gardeneating machine.
Grow coleus, pelargoniums or geraniums, cabbages, chrysanthemums or dahlias, and the leaves will disappear before your eyes