'Waiter, waiter, there's a fly in my soup!'

This fly (a St Mark's fly I think) has come to grief in one of the reservoirs of water that collect around the stem of the teasel plant where  each pair of leaves forms a sort of cup. These little pools act as  bug traps into which slugs, caterpillars and insects of all kinds  fall  and drown. (The generic name for teasel, Dipsacus,  comes from the Greek word for being thirsty on account of its propensity to hold water this way.)

As long ago as 1875 Francis Darwin, son of Charles, noticed that 
'The stalk of the plant is covered with sharp prickles, but these cease where the stalk dips into the water in the cup. If it were not for the loss of the prickles at this point, a ladder of escape would be provided for the drowning victims. I have seen a beetle struggling to get out, and observed his tarsi slipping over and over again on the smooth stalk. The cups undoubtedly form a most efficient trap.'

He also speculated that the teasel plant derived some benefit from the remains of its victims but it was not until very recently (2011)*  that this was confirmed by a controlled experiment in which some teasel plants were supplied with dead maggots and compared with others whose reservoirs had been kept bug-free. It turned out that the plants that had been provided with nutrition were 30% more successful at setting seed than those without,  thus proving what had long been suspected: that the teasel is a carnivorous plant.

However, unlike  better-known carnivorous plants such as  sundew, the teasel takes its protein in the form of soup rather than fresh killed.


*http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3060873/