Bishop’s Stortford Independent Nature Notes columnist Jono Forgham visits Sawbridgeworth Marsh Nature Reserve
Time was at a premium over the bank holiday weekend and, weather wise, Sunday looked to be the warmest and brightest day. I decided to concentrate on a single habitat to see what I could find and chose the wonderful Sawbridgeworth Marsh.
This reserve can be found along the lane from near Sawbridgeworth railway station to Gaston Green and Little Hallingbury, less than a mile on the left soon after passing the first houses on the lane. Parking is limited to two cars in the layby. If full, I suggest the car park at The Maltings and then a short walk.
Having completed an insect survey in a local wood in the morning, I arrived at the marsh around 1pm and was immediately struck by the amount of birdsong. Standing at the entrance, I could hear sedge warbler, reed warbler, whitethroat, blackcap and reed bunting. What a start! The first two species were new records for me this year.
At the entrance, a metal five-bar gate, is an information board. The paths are not wide, but in several places a handy boardwalk is in place. Wellies are advisable as it was very wet after recent rainfall.
Upon entering, it was clear that there were many flowering plants to check. Marsh marigolds were everywhere, with the rarer marsh valerian also pushing through whilst cuckoo flowers were more sporadic.
I took the boardwalk to the southern end, a wooded habitat with a small pond and plenty of nettle cover. I changed lenses on the camera, fitting my macro lens, and went off in search of insects. There were many. A female banded demoiselle damselfly posed for a close-up shot. These are metallic green with translucent wings, whereas the males are metallic blue with a black band across their wings. Both males and females were seen in good numbers, but, I suspect, not at their peak just yet.
There was plenty of common comphrey, with its bell-shaped flowers attracting many bees of several species, whilst the garlic mustard appeared to be more attractive to butterflies. In a short time I saw orange-tip, peacock, green-veined white and a female brimstone, the latter showing its delicate green colours as opposed to the bright yellow male.
The orange-tip is frequently found around the garlic mustard plant as it is a main larval foodplant for the caterpillars to feed upon. Females often rest upon the plant to attract a male as well as egg-laying upon it. I use the leaves to make a fine pesto as the plant is of the onion family and the leaves have a garlic flavour (taxonomic name, Allaria petiolata).
I moved to the pond, where lesser pond sedge was coming into flower and last year’s bullrush seed heads were breaking up to spread their seeds. Great tits and blue tits feed upon these, helping them to disperse on a windy day.
On the sedge was a long-legged spider: a Tetragnatha species, either T. extensa or T. montana. The yellow colours of this specimen hinted at it being the former, but microscopic study is required to fully guarantee identification to species level. These spiders are also known as long-jawed orbweb spiders.
I checked for signs of water voles but none was apparent. I’m sure they are to be found upon the reserve.
A black insect rested upon some sedge. I stooped to check this out: an ichneumon wasp, of which there are well over 2,000 species. This was one I was not familiar with, so I took care to get sharp shots for identification later at home.
After a fairly lengthy study, I thought this species was Rhyssella approximator. On further checks, I discovered there are only 16 records of this insect in the UK. Whilst I was fairly confident of my identification, it certainly required verification by an expert.
Consequently, I forwarded a set of photos to Jaswinder Boparai, the leading authority on ichneumon wasps, spending his time studying them at the Natural History Museum. He confirmed the wasp species as Rhyssella approximator. He’s 90% sure it is that species and could only be 100% if he was to actually examine it. However, it will be recorded as the rare species with the addition of “unconfirmed”.
For every moth and butterfly caterpillar, there is an ichneumon wasp that lays its eggs on or in the larva. Jaswinder is working to establish which wasp species is parasitic upon which caterpillar species. With over 2,000 species, it is a life’s work.
I moved on, following a path that runs alongside the Stort backwater, adjacent to the railway line just before Sawbridgeworth station. Here, more sedge warblers, wood pigeons and chaffinches before I heard one of the most distinctive bird calls: a cuckoo.
This is a very secretive bird that often uses sedge warbler nests to lay its solitary egg. The male bird was calling from the northern end of the reserve, so I headed off to see if I could find it among the coppiced willows. As I headed off, I heard a cuckoo call from the southern end. I never did discover whether this was a second bird or the original one that had commuted over to the far end. The chance of finding it had gone, but my first cuckoo of the year.
By now, I had reached a reed habitat and waited for one of the reed warblers to show long enough for a photo. Fortunately, I didn’t need to wait long as one popped up with insects in its beak.
Then, another pleasing bird was heard. Over the noise of trains, planes and cars, a grasshopper warbler was calling. Another first-for-the-year species. The call of this skulking bird is very similar to the song of a grasshopper, a long clicking call. It is referred to as “reeling” as it also reminds people of the sound of a fishing reel being wound in. The song can go on uninterrupted for 30 seconds or so. As I expected, no sign of the bird. They usually call from more prominent song posts at dawn and dusk, so I decided to return at first light on the bank holiday Monday.
A hoverfly species alighted in front of me, Melanostoma scalare, a regular insect for early May, easily identifiable by its pale underparts. This one was feeding on cow parsley pollen.
The air was heavy with the scent of hawthorn blossom as the damp conditions finally soaked through my boots. I should have followed my own advice and donned wellies.
A male muntjac stared as I waded through ankle-deep water, where I came across a good stand of ragged robin in full flower. A plant that indicates a good habitat. Very pleasing to observe.
By now, the bright blue sky and some of the best temperatures of the year had dissipated to be replaced with heavy, low, grey clouds. I headed back to the car and home to work on the ichneumon wasp species.
Bank holiday Monday dawned with reasonable light and I was back on the reserve at 5.30am. Once again, good birdsong but, disappointingly, no showy grasshopper warbler, or “groppers” as they are known in the trade.
I completed a circuit of the reserve in even more wet conditions thanks to a heavy dew. The place was covered with spiders’ webs, all looking amazing in the early-morning light, bejewelled with the dew. Not the greatest light for photos, but well worth the effort nevertheless.
Many of these webs will have been constructed overnight by the Tetragnatha species, whilst others looked to be made by tiny moneyspiders, the Linyphidae group. One species in particular build a web reminescent of a hammock. This will be Linyphia triangularis, the common hammock weaver. Another species evident by their overnight webs was Larinioides cornutus, the furrow spider.
Certainly, a magnificent and rare habitat. Very fortunate to have this local to us and also most fortunate that it is kept in top condition by a band of dedicated volunteers, led by Bob Reed, who, in 2021, was the recipient of the 1875 award from Hertfordshire Natural History Society. It is presented annually to a naturalist that is “an outstanding contributor to natural history in Hertfordshire.” A most appropriate acknowledgement of all Bob has achieved over many years.
Finally, if you are planning a trip to this reserve, please note, dogs are not permitted, and do take care if walking from Sawbridgeworth along the lane. Very much worth a visit.
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