Crab spider lurking in a teasel seedhead

 Teasels Dipsacus fullonum are wild flowers that just keep giving. Bees love their flowers, goldfinches eat their seeds and the empty honeycomb seed heads survive for months, providing winter accommodation for tiny insects - but not without hazard.

This teasel seed head, at my local Low Barns nature reserve, had a predator lurking amongst its prickly seed chambers. It’s a tiny crab spider, waiting to intercept any small insect arrivals.

Crab spiders don’t spin silken webs, but often lurk in flowers with their front pair of legs held like crab claws, ready to grab unwary prey. Some species can change their colour to blend with their surroundings, making them very effective ambush predators. 

This one was tiny and they are notoriously difficult to identify, but I suspect it might be a female running crab spider, Philodromus dispar.

Killer Teasels?

Over a century ago there was considerable debate as to whether the teasel Dipsacus fullonum was a carnivorous plant. It’s not difficult to see why – the bases of the leaves clasp the stem to form a large cup that fills with rainwater and this soon fills with drowned insects. The criteria for a plant being truly carnivorous are that it must lure its prey, trap it, kill it, digest the victim and absorb the nutrients that it releases. Teasel fails on the fourth of these criteria and probably the fifth too – it doesn’t secrete any enzymes of its own to digest the prey and there’s no clear evidence that it absorbs any nutrients from the soup of rotting flies in its drowning pools. But it can certainly lure and trap its prey, in much the same way as a pitcher plant. This bumblebee was presumably attracted by the water in the leaf bases and as soon as it landed it slipped into the water. From that moment on it was doomed. It struggled to climb out but its wet feet slipped on the shiny, smooth surface of the stem and leaf bases. I thought about rescuing it but within less than half a minute it had fallen back in, become totally saturated and had drowned. The teasel leaf bases soon fill with dead insects and must also have a rich population of bacteria and fungi that can digest them, so maybe it’s time for another look at the eating habits of this plant, to check again at whether it derives any nutritional benefits from its decaying captures. Birds certainly do – I’ve sometimes seem blue tits and great tits raiding this gruesome larder.