Nature report from Castle Park in Bishop’s Stortford

Nature Notes columnist Jono Forgham covers your fortnightly look at nature around Bishop’s Stortford

I attended the official opening of the rejuvenated Castle Park at the start of the month. Councillors and the town’s MP were present among the interesting stands manned by community groups that support and use the park and its facilities, including the Markwell Studio.

The Coda Falconry stand was particularly interesting, displaying three owl species and several falcons. I was also interested to note the wildflower border around the base of the Waytemore Castle Mound, whose array of colour was attracting several bee species.

I hadn’t decided where I was going to do my next Nature Notes wander, but there was so much to observe in the park and then along the River Stort to Grange Paddocks that it seemed appropriate to mark the official opening with a report.

I mentioned on the wonderful Stortford Nature Facebook site that I would be happy for people to come along with me, so I met Carole, Anne and Chris at the new Terrace Park Café and Kitchen at 10.30am.

We began by searching the flower borders. Many species here, including several papaver species upon which both Bombus vestalis (vestal cuckoo bumblebee) and Bombus terrestris (buff-tailed bumblebee) were feeding.

Other good native species present that are wonderful for pollenators were loosestrife, cornflowers, wild carrot and yarrow. I noted other bee species, Bombus pascuorum (common carder bee) and Bombus hypnorum (tree bumblebee).

We then checked out a few tree species, some clearly non-native, which I was not too sure about, before we picked up the Tarmac path parallel to the river and headed towards the leisure centre.

A wide variety of vegetation was to be found in the verges here. A few individual Himalayan balsam were noted by Anne and Chris. They are members of Friends of Castle Park and one of their regular summer jobs is to remove as much of this balsam as is feasible. The group have clearly done a good job, with just 10 or so plants noted. I am sure these will have been dealt with soon.

Himalayan balsam is a highly invasive plant that rapidly colonises a riverbank and smothers out the native species. It has a very successful seed dispersal system. The pods dry out until they spring open, flinging seeds up to 3m (10ft) away. These seeds can survive in water and consequently travel downstream before being deposited on a bank, where they grow vigorously.

Hogweeds, horseradish, nettles and burdocks were all to be found on the riverbank. A check of these gave views of species such as Pisaura mirabilis (nursery web spider), Anthophila fabriciana (nettle-tap moth), hoverfly species Eristalis pertinax and Cepaea nemoralis (brown-lipped snail).

Just before arriving at the weir, I noted several white and brown shieldbug species. These were not the full adult version and therefore show a different colouration and patterns on the abdomen. These were the final instar of the bronze shieldbug (Troilus luridus), a good find.

All insects go through a series of changes once they have emerged. These are known as instars. Shieldbugs usually have three instars: early, mid and final. Others can make up to five changes.

My companions then pointed out a small and colourful ladybird species, the 22-spot ladybird with its improbable taxonomic name of Psyllobora vigintiduopunctata!

At the weir, a flash of blue and orange signalled the presence of a kingfisher, but even though we looked for it, it was not noted again.

However, a check upon tree species, in particular the leaves, did offer records of several leaf-mining caterpillars and other larvae. On a cherry leaf was the very distinctive leafmine of the micro moth Lyonetia clerkella.

A leafmine is where the adult insect lays eggs upon the leaf and, immediately upon hatching, the caterpillar eats into the leaf and resides between the two layers of epidermus. As it eats its way around it leaves telltale markings. These are often long tunnel-type marks that increase in width as the larvae increase in size, whilst other species just munch a large area where they are.

By the large footbridge is a solitary elm tree that, so far, has not succumbed to Dutch elm disease. A quick search of the leaves here and I found what I was looking for: the very obvious eating pattern of the Aproceros leucopoda, the elm zigzag sawfly. This species, that has arrived in the UK, was originally found in southern Asia. The leaf I picked to show others actually had the larva happily munching as we looked and managed a few photos.

We continued and upon an alder leaf I noted a large group of shieldbugs, again the final instar of the parent shieldbug, so-called because the adult will guard the eggs and the young first instars; I suspect, with a little searching of nearby leaves, we would have encountered the adult. There must have been about 20 immatures on one of their favourite trees.

Over the entrance road and onto Grange Paddocks. The river here is very overgrown, so no chance of seeing any water voles. Moorhens called and several mallards paddled about. A sparrowhawk flew into a large poplar, sending the resident wood pigeons off in all directions.

Several fly species were seen along this stretch, including the well-marked Graphomya maculata and the colourful Lucilia species, one of the commonly called greenbottles.

Also here, among nettles, was a fully grown Araneus diadematus, the garden cross spider, right in the middle of the immaculately made web. These spiders appear in early autumn and will be in lots of gardens. They construct their web in the late afternoon so as to catch moths at night. They have a very distinctive pattern on them that usually features a white cross. Worth looking out for at dusk and early morning in your garden. They are often found on their web near a light source as this will attract the moths.

Around several meanders brought us towards the footbridge to Cannon’s Mill Lane. Here, a willow had shed a large bough. I noted the What3words location, took a few phone snaps and sent details to the council so they can make the tree safe as it overhangs the footpath and benches.

It was here that my three companions headed off home, so I turned around and headed back to Castle Park. I popped into the leisure centre for a sandwich and soft drink before continuing along the river.

I checked more vegetation as I went, encountering a green shieldbug whilst hearing blue tits, great tits and long-tailed tits. I made a brief check on the river in Sworder’s Field where there is a river dipping platform. Shoals of small roach and chub were to be seen in the shallows.

Another check on the flower beds yielded still much bee activity, before I headed to the car park and off home with close on 200 photos to process.

This is a very accessible walk for all, the round trip being just under three miles and plenty can be seen in any season. In winter, the alder trees can be full of siskins, often accompanied by smaller numbers of lesser redpolls. Once the leaves have dropped, birds become easier to spot and it is then that one of the over-wintering kingfishers can be seen.

Mobility scooters and wheelchairs can follow the hard paths around the park and riverside, and there are now Tarmac routes around Sworder’s Field. Always a wonderful wander.

Not too many towns have such an impressive green corridor that comes almost into the town centre. I look forward to attending events in Castle Park into next year as well as keeping an eye on the natural history of the habitat.