Given that worm casts are such a prominent feature of the meadows at this time of year, I thought that I’d better find out a little bit more about them and I found a nice article written by two Sussex University lecturers about the worms found on campus: There are 27 species of earthworm in the UK, 19 of which are common and different species are found in different soil types and at different depths feeding on the decomposing remains of plants, which they eat as they tunnel along, ingesting this as well as some soil. Only two species produce surface casts: Allolobophora longa and Allolobophora nocturna – both deep burrowing species that live in permanent burrows and the casts are a mixture of faeces and this ingested soil coming out of their other ends. Worm activity is very dependant on temperature and moisture level. In winter the temperature is too low and in summer the ground is too dry and so worm casts are especially prevalent in spring and autumn.
This morning we had a Herring Gull in the first meadow charming the worms out of the soil by paddling with its feet up and down which causes the worms to come to the surface and then into the jaws of the gull. Apparently Herring, Common and Black Headed Gulls do this on Sussex University Campus grounds.
Why this foot paddling causes the worms to emerge out onto the surface is the subject of a bit of confusion. Charles Darwin, who was interested in earthworms and, in fact, wrote his last book on the subject, thought that perhaps the vibrations caused by this were similar to that of a mole moving through the soil and so the worms were trying to evade that worm predator only to fall victim to another. Another suggestion is that the vibrations are like heavy rain and so the earthworms come up to escape drowning. However, often gulls are seen doing this worm charming in shallow water or on wet mud which are conditions where moles do not go and additional water as rain is unlikely to increase the risk of worms drowning and so perhaps the real answer to this conundrum is yet to be discovered.