I think I may have spoken too soon about blackbirds being in balance with vine weevils in our balcony garden. The blackbird has discovered the delights of window box strawberries and the weevils have been feasting on the clematis. For now the weevils do seem to be going for the older flowers that are already starting to fade, and the paper cut out effect has a certain charm, but the holes in the leaves are spreading fast and the plant is starting to look sorry for itself.
A couple of weeks ago I spotted a long-snouted, matt black, dusty-looking insect crossing the kitchen floor. To avoid treading on it, I scooped it up and tossed it out the door onto the nearest plant before I stopped to reflect on what it actually was. Vine weevil control in the balcony garden has mostly amounted to squishing eggs (me) or snacking on grubs (the blackbird). Here was a weevil that had survived our combined attacks to reach adult form, and I’d just lost it among the prickly stems of the rose bush.
A few days later I started to notice the tell tale arcs of weevil munching, around the margins of some rose leaves and then on the clematis which twines through the stems of the rose. Unlike caterpillars, that tend to walk as they munch, weevils hang on tight in one position while they swivel their head from side to side, leaving neat semi-circular holes that could have been cut out with a hole punch. A few flowers with cut out petals are an interesting curiosity but unfortunately vine weevils are a serious horticultural pest with a voracious appetite. Even one adult weevil can do a lot of damage.
Vine weevils thrive in container grown plants. They arrived on the terrace last year with two new pots of Tiarella, planted out in one of the large boxes. The leaves of Tiarella have deeply cut margins, so I only noticed the extra cut-outs just before the first plant wilted and keeled over, chomped off just below ground level by the hungry grubs. I scrapped both plants (with the complete root ball) and worked through the box with a hand fork, squishing all the eggs and grubs I could find. The blackbird took over after that, tossing compost out of the box and clearly finding something good to eat. Between us we missed one.
Adult vine weevils hide up during the day so last night I went out after dark with a torch. Sure enough, there was one large weevil, chomping its way through a rose leaf. It looked just like the one I’d rescued from the kitchen floor. I didn’t have the heart to squash it (here speaks someone who kept pet woodlice as a child) so I dropped it into the rubbish sack, along with a supply of badly munched rose leaves.
I searched thoroughly with the torch and couldn’t find a second weevil, but that’s probably not the end of the infestation. Male vine weevils appear to have become extinct as all the species are now female, able to reproduce parthenogenetically. Just one adult weevil is all it takes to produce fertile eggs, so the blackbird may have weevil grubs to snack on for some time to come.