Having had the good fortune to finally identify, after four years, the Mystery Brassica growing in our garden (all we'd needed to do was attend a field trip to look at arable weeds), I thought I would re-iterate why we tolerate Wild Radish springing up randomly within our environs. In a nutshell, or more accurately in a seed pod, the local wildlife loves it.
All manner of insects flock to the flowers: several butterfly species (Green-veined and Large Whites); moths (Silver Y); and all manner of hoverflies, to name but a few. The Large Whites lay eggs on the brassica as the leaves are the food of choice for their caterpillars.
At this time of year, Greenfinches, which have been strangely absent for the rest of the year, suddenly appear to chomp their way through the Wild Radish pods, leaving the ground beneath the plants covered in a neat layer of evenly-sized remains.
Also at this time, the Large White caterpillars set off to find a safe place to pupate, often making quite a journey, as we usually find some on the walls of the house.
Quite whether the effort is worth it is debatable, as most seem to parasitised by a small wasp, whose own larvae emerge from the caterpillars to pupate themselves. Local bug guru LJ reckons these might be from the wasp Cotesia glomerata.
And here, below, is the remains of a past parasitisation with, alongside it, a recently-arrived Large White caterpillar preparing to pupate. It doesn't bode well, does it?
Still, every year, there are Wild Radish plants aplenty, a host of Large White butterflies, several Greenfinches and, apparently, parasitic wasps, so some sort of order is being successfully, if chaotically, maintained.
Interestingly, whilst Large Whites will feed on many types of brassicas, the Wild Radish is actually the favoured food plant of the Green-veined White. As mentioned above, we see these regularly in the garden, but I can't recall ever finding their caterpillars. Must try harder!