WEEDS – LIFE IN A THISTLE

Weevils are cute.

No, really.

Beetles tend to be sturdy and a little alien, flies have those weird multifaceted eyes, but weevils are like the Disney version of an insect, with big eyes and a long ant-eaterish nose.

We were out chopping and spraying weeds in a revegetation area when I noticed that many of the Scotch Thistles (onopordum acanthium) I was hoeing out were looking unusually scrawny and punctured with multiple holes.

I immediately dropped my hoe and started looking more closely.   Frank had told me there were some weevils attacking the thistles on Adnamira, but I hadn’t seen them before.

It’s nice to have an insect on your side.  Despite my Scottish heritage, I have no great love for Scotch Thistles.  When we drove from Canberra to Melbourne on the old Hume Highway as kids, we used to pass the giant thistles of Jugiong that seemed a warning of what would happen if no-one paid attention.  They crowded together as if they’d like to break out onto the road.

CSIRO over several years has released a number of different biological controls for onopardum thistles, of which stem-boring  weevils are just one.   There are three different weevils and a moth (details here).

I want them all.

It was pretty clear that the most fully-weevilled plants were not putting up flower heads, or if they were, they were stunted and small compared to another group down by the river that were much taller and seemed to have no bite marks.   I was fairly sure the largest and yellowest of the weevils I saw were the stem-boring weevils (lixus cardui), but when I asked for an identification from Kim Pullen at the Friends of Grasslands workshop, he kindly pointed out it was a seed-head weevil (larinus latus).   They lay eggs on  the outside of the head of the thistle.  The young larvae then bore their way inside, eating all the way.    The adults browse on the leaves making the holes I was seeing and then hibernate through the winter.

There were also weevils having an exciting time hanging athletically upside down.  Hope they make lots more weevils.  These ones were a little smaller, browner and may possibly have been the stem-boring weevil (lixus cardui).  That’s wishful thinking.

Further down the paddock, there was a different drama going on.  I found a spider that seemed to have a group of earwigs cornered.  They burrowed as tightly as they could into the prickly crevices, while the spider lurked outside.  I haven’t been able to identify the spider as yet and the earwigs seemed to be the European introduced ones.  I left the weevils to their thistle world, and went to find weeds that needed my attention.  There are plenty of them.

UPDATE:  I found both types of weevils on the Esdale side of the river, doing a good job.

I had a go at identifying the spider, and think it’s probably an orb-weaver of some sort, judging from the body-shape and the weird humps on its back.  As they hide during the day and feed from their web at night, it probably didn’t have those earwigs cornered, they may have just been annoying neighbours pushing it out to where I could see it.