A sultry, windless afternoon and the air above the garden path is shimmering. It’s too hot to do anything much during this heat, other than stand here and watch the carnage unfolding on this 7ft-tall cardoon plant.
It was early June when we first noticed the small clusters of black aphids. Looking closer, we watched a long column of ants, from the nest under the paving stone, climbing the stems, tending the aphids, stroking them with their antennae and legs, encouraging them to produce drops of sweet honeydew.
Aphid “farming” by ants has been documented for centuries and was meticulously observed in 1882 by Sir John Lubbock, MP, polymath and friend of Darwin, in his book Ants, Bees and Wasps. He watched aphid colonies grow, noting that their ant herders moved some to new locations on the host plant, founding new colonies. And that seems to have happened on our cardoon. By early July new aphid colonies had proliferated and flower stems were soon covered with thousands of sap suckers, so many that the plant’s great armoured inflorescences bowed their heads for want of sustenance.
Then came flying ant day. The herders’ colony rapidly declined – but the aphid population explosion continued, raining droplets of uncollected honeydew, coating leaves in sucrose. Now it was the turn of hordes of hoverflies, arriving to lap up the sticky sweetness and lay their deadly eggs among the aphids. When the predatory, slug-like larvae hatched they wreaked havoc.
Today the ants have gone, and the stems and leaves have the melancholy post-apocalyptic air of a battlefield, strewn with withered aphid corpses. Seven-spot, 14-spot and harlequin ladybirds roam the leaves, mopping up huddles of survivors. More opportunists arrive: neon purple and metallic blue jewel wasps; agitated, hyperactive ichneumon wasps; scurrying spider mites and a host of small flies.
The aphid infestation is almost over. Wilted flower buds are reviving and some, a little smaller than usual, have opened their spectacular crowns of blue florets, beloved by bumblebees.
Over the last month we’ve witnessed a great pyramid of interconnected life assemble here, an unfolding drama with an ever-changing cast. One puff of insecticide, six weeks ago, and this enthralling pulse of biodiversity would never have happened.
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