p2756v, the situation is complex - far more complex than getting out the spray kit & giving the natural environment a good dose of poison. Not that you would even remotely entertain the idea, of course, but there are people out there whose trigger fingers itch like crazy when they see a caterpillar.

An over abundance of caterpillars is a sign that there aren't enough natural predators about. This is usually due to bushland destruction because the bushland is what supports populations of predators. Native Cuckoos are a prime predators of caterpillars & most, if not all, native Cuckoos are migratory so an important method of controlling out-of-control populations of caterpillars is to ensure there is sufficient bushland far & wide across Australia. Other native birds such as Australian Magpies & Thornbills also predate caterpillars so restoring natural ecologies which support such birds is a good way of controlling caterpillars & keeping the spray kits in the garden sheds.

I'm wondering, then, if the healthy Crinum pedunculatum along the motorways are part of a healthy ecosystem. Are there plantings of native, particularly indigenous, plants along the motorways? If so, then they may be supporting populations of predators which, in turn, are keeping the caterpillars under control.

Thanks Woko, you are correct re the ecosystems however I don't have the years ahead to muster all my neighbours in the 25km radius to correct "my" situation. I have more natives than the motorways where I've noticed unblemished crinums. I suspect it is a possible film that has saved these. I was looking for more immediate remedies that perhaps someone had up their sleeves, but thanks anyway on your part.

The tragedy for our native vegetation generally is that it takes a few moments with a bulldozer to knock it down but aeons to even go close to restoring it to anything remotely resembling its former self. In the meantime we're stuck with dealing with the consequences, among which is an overabundance of caterpillars. Welcome to our new over-developed world!