Val Bourne Wildlife

Your with Val Bourne, AG’s organic wildlife expert Gardening Week

Large cabbage white butterflies lay their eggs in batches, which take about two weeks to hatch into caterpillars Cabbage white caterpillars can decimate nasturtiums, but wasps collect these insects to feed larvae in their nests

The common wasp (Vespula vulgaris) feasting on aphids

Murder most foul

Val looks at the brutal methods used by wasps to kill prey

ANY of you will know that I am a great fan of social wasps, because these stripy

Mmeat-eating bees rid me of lots of pests. Last year they cleaned up clusters of newly emerged large cabbage white caterpillars, because lockdown prevented me from getting proper butterfly netting. The only netting available had large squares, so the butterflies just flew straight through and laid their eggs. When I saw the clusters of tiny large white caterpillars my heart sank, and I tried to rub them away with my fingers. The messy green gunge took me straight back to my childhood, because collecting large cabbage white caterpillars was my first gardening job.

I was assigned this responsible task aged four years or so, on a sunny summer’s morning, and my grandmother armed me with a small bucket full of salty water. I was meant to drop the wriggling

“I had never seen anything like this before” TIP

caterpillars into the salt-laden bucket as I picked them off, but my four-year old fingers were not quite dextrous enough. I squashed several of them in the process and finally decided to put the ones I did manage to move into an empty bucket, rather than drown them. I trudged up the back alley and deposited them at the bottom of a neighbour’s garden and they probably marched back.

I can still sense the green slime on my fingers and I remember being careful not to wipe it on my polka-dot summer dress! That green slime is full of mustard oil, imbibed from the brassicas it munches, and it tastes as unpleasant as it looks. Consequently, mature cabbage white caterpillars are extremely unpalatable to predators. Even my chickens turn up their noses!

Not all members of the brassica, or cabbage family, are edible vegetables. Some have pretty flowers and these include honesty, sweet rocket, sea kale, sea stock and nasturtiums. Nasturtiums often get cabbage white caterpillars on their leaves by early summer, and I have grown these on my vegetable plot as an early warning system. I’m not sure if they kept the blighters off my edible cabbages and kale, though!

I grow the white sea stock, Matthiola incana ‘Alba’ , on sunny, dry edges in my garden. I love the grey rosettes of foliage in winter and it produces highly scented white flowers in May. Each flower has four petals, a characteristic of the cabbage family. My sea stocks endure from year to year, as long as I stop them from setting any long narrow seed pods. If they set seeds, they die.

One June day I spotted cabbage white butterfly caterpillars munching the rosettes of my sea stock foliage, but I was on my way out so I had to leave them to it. When I returned at lunchtime, they were being carved up by a team of wasps and each wasp was flying out with a section or two. My jaw dropped, because I had never seen anything like this before. However, I didn’t witness the first stage in this brutal murder. The massacre would have begun by each wasp stinging the caterpillars several times. This is the classic technique used to incapacitate and subdue their prey.

Within hours my sea stocks had been rescued. Each tasty morsel was taken back to the nest to feed the hungry larvae and the wasp would have been rewarded with a sugary droplet, which is a waste product from the larvae. The trouble starts when the nest becomes empty. The wasps have to look for their sugary fix elsewhere.

This hunting process goes on all summer, and Professor Adam Hart, an entomologist working at the University of Gloucester, writes that, “It has been estimated that the social wasps of the UK might account for 14 million kilograms of insect prey across the summer. A world without wasps would be a world with a very much larger number of insect pests on our crops and gardens. ” You can find out more on the Big Wasp Survey ( bigwaspsurvey.org).

Kniphofias provide nectar for wasps

August-flowering kniphofias and crocosmias provide lots of nectar for wasps that are in need of a sugar fix.