Category Archives: Olwen Williams’ monthly reports

December records

snailshellDid you know that spiders sometimes eat snails? Hanging from spider silk attached to the eaves above the back door, I found this empty shell of an immature garden snail. Wondering how on earth it could have got there, I consulted the
Oracle and found several records of spiders attacking and eating snails, including a video clip.

It was at the site of a garden spider web (Araneus diadematus).

The garden is generally quiet at this time of year, but after some unseasonably warm days, I have heard wood pigeon, green woodpecker, song thrush and wren all calling as if it were spring. A great spotted woodpecker sat at the top of a large tree, calling persistently, but I have not yet heard him drumming. By the river, siskins are investigating the alder trees – they love the seeds. My front garden has been adopted by a robin, keeping guard over the feeding station from a perch in the quince tree.

Cambridge is generally surrounded by green belt – fields and agricultural land. Some of their hedge boundaries are ancient. Oliver Rackham, an eminent Cambridge woodland ecologist, described the application of Hooper’s Rule here. Hooper maintained that the average number of woody species in a 30 yard stretch of hedge was roughly equivalent to the number of centuries the hedge had been there. By this rule, there are many hedges between Cambridge and Grantchester which must be 500-600 years old! I wonder how many there are which are threatened by the proposed development of West Fields for a busway? If you know of hedges in Cambridge which may be interesting and ancient, we would be very happy to come and survey them – please get in touch.

Olwen Williams

November records

At this time of year, autumn colours are always a race between frosty nights and high wind.  Well, the frosty nights have come and the colours deepened, but now many leaves have blown off in the wind, so walking has become a childhood pleasure, through drifted piles of green, yellow, pink, red, plum and brown, to match the November fireworks.



Some insects are still active.  Ivy flowers provide a valuable food source in November and a late wasp was seen on these (above). A common darter was spotted on a stone wall (right).  Under a rough web, on a fallen leaf, a 3mm bright green spider lurked – Nigma walckenaeri (below).OLYMPUS DIGITAL CAMERA

It is always a surprise to visitors that cattle graze the meadows along the Cam, even in the middle of the city.  Over the last few weeks, they have mostly been housed for the winter, no longer depositing their dung pats across the water meadows.  However, under the pats it is far from dead!  The larvae of dung beetles and dung flies survive over-winter as chrysalises, to emerge as adults in the spring.  Fungi break down the dung, worms and plants invade it, rain and frost contribute to decay and soon the nutrients are returned to the soil.

There are still lots of other fungi around.  In Paradise Local Nature Reserve, a huge willow tree was felled about three years ago, after it became dangerously decayed in the middle.  The logs were piled beside the path and now host various bracket and other fungi.  Altogether, I found 15-20 different species in the wood, including oyster mushrooms.

Olwen Williams, 11 November 2016

October update

After a long and mostly hot summer, temperatures are now dropping, especially at night and we can anticipate some autumn colours in the trees.

Walking through the Paradise Local Nature Reserve, I came upon a kingfisher moving ahead of me. Several times, he perched and then splashed down into the water in search of dinner. Kingfishers are the ultimate specialists, in terms of both diet (fish) and nesting place (a hole excavated in a steep bank, out of reach of rats and other predators). I remember that one year, there was a nest in an old drainpipe in the river wall of Clare College, right in the centre of Cambridge.

My cat brings me a variety of ‘presents’! On one occasion a live kingfisher was handed over unharmed and I was able to take it back to the river, where it flew off with an indignant squawk. This week, I found a Convolvulus Hawk-moth on the mat. A night flyer, I would probably never have seen it resting during the day, its grey speckled wings and pink and black abdomen blending perfectly with tree bark. These large moths are autumn migrants from Africa.

This year has been a spectacular year for snails and slugs. Under a pot in the garden, I found several large Black Slugs, Arion ater (which can be brown, yellow or even white) busy with their autumn egg- laying, after which they will die. Between August and October, each individual may lay multiple batches of up to 150 eggs, so if, as a gardener, you want to reduce next year’s population, clear as many eggs as possible! Otherwise leave slugs as part of the ecosystem, as they clear detritus and even dog mess and provide food for hedgehogs and others. I notice my slugs are parasitised by slug mites, Riccardoella limacum, tiny white creatures which run around the outside of the slug and into the lungs via the pneumostome. It reminds one of the rhyme, “Big fleas have little fleas, upon their backs to bite ’em, And little fleas have lesser fleas, and so on, ad infinitum.”


11th October

Even the most urban parts of our city can hold wildlife.  October 10th was warm and sunny. Whilst walking through the underpass and the centre of the roundabout connecting Newmarket Road and Elizabeth Way, I noticed how alive with insects the rosemary was. Although I only definitely identified Honey Bee and Common Wasp, the sheltered nectar was clearly very popular with wildlife, providing a food resource in a somewhat concrete part of town.

Louise Bacon

Intro to the project by Olwen Williams

Cambridge City Natural History


The city of Cambridge includes grand buildings, new and old houses, streams, lakes, cemeteries, water meadows, gardens and recreation areas. The river Cam runs through the centre, forming a focal point for residents and visitors alike.  It is a small city, roughly eight kilometres square, densely populated but full of green spaces. Nowhere are you far from the countryside and even within the city, wildlife abounds.


This project, planned to last for 3-4 years, aims to increase public awareness of the diversity of plants, animals and fungi within the city and to involve everyone in documenting Cambridge’s natural history heritage. As part of the programme, a garden will be chosen in each square kilometre across the city and surveyed intensively.  Initial studies show that as many as 70 native plants may be present in an average garden and moth trapping in north Cambridge turned up a beautiful privet hawkmoth.


Just now, the season is turning from summer to autumn.  Tawny owls – two males and a female – were calling last night from the tall trees.  Other birds are quiet, in autumn eclipse.  There is no longer the noisy racket from the heronry by the river, suggesting that this year’s young have at last fledged.  The horse chestnut trees, whose leaves are attacked by the larvae of a moth, have turned brown and prematurely shrivelled. Although this moth only arrived in the UK in 2002, it has spread rapidly northwards.  Spiders abound – the webs of the garden spider lace the bushes. Butterflies, bumble bees and dragonflies persist, but in smaller numbers than before. A mating pair of Willow Emerald Damselflies were seen in the Botanic Garden on Sept 4th. This species was first recorded breeding in the UK in 2007 and seems to be expanding its range