Country diary: A great pretender lurking on the riverbank

Great swathes of water mint along the River Hiz have attracted an astonishing array of pollinators, given the paucity of insects this summer. Almost every pale lilac flowerhead hosts a different species – green-veined white and small heath butterflies, mint moths, drone flies, honeybees and bumblebees.
The drone flies are methodical, probing each tiny tubular flower in turn, while the green-veined whites flit from cluster to cluster. A wasp plumehorn (or lesser hornet hoverfly) climbs into view, its honey-yellow abdomen barred with black. Two huge, brown compound eyes meet on the top of the head, indicating that it’s a male. Named for its mimicry and feathery aristae (bristles on the antennae), this hoverfly species has larvae that feed on wasp and hornet grubs.
With his warning colours and a wingspan of 30mm, the plumehorn is impressive, but he’s not the most captivating pretender on the riverbank. Lurking in the long grass, I spot a bulbous yellow abdomen with black scalloped banding, then another – and 16 striped legs. They belong to a couple of female wasp spiders (Argiope bruennichi), another species that mimics wasps to protect itself from predation and which was first recorded in Hertfordshire in 2005. Wasp spiders mainly prey on grasshoppers, but – despite several prospective victims in the vicinity – these two are catching pollinators. Three inert parcels already dangle from their orb webs. One looks to be a wasp and, as I watch, a black muscid fly blunders into the sticky silk and is swiftly encased.
I’m surprised that neither web has an obvious stabilimentum (a line of dense silk whose function is still under debate). When I found my first wasp spider in 2021, 99 years after the UK’s first record in East Sussex, it was the stabilimentum that gave it away, zigzagging conspicuously from the centre of the web to the base. Perhaps these are old webs, or the UV-reflecting structure is unnecessary in this location, for these spiders have chosen the perfect ambush site.
Although most of the pollinating insects will leave the riverbank sated, some have unwittingly supped their last. Lured in by a cocktail of minty oils and sweet nectar – a chalk stream mojito – all that remains for them now is Death in the Afternoon.
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