Monthly Archives: August 2013

Autumn Ladies-tresses on Bristol Downs

There are a few flowering plants that wait till the end of the summer before flowering, and Autumn Ladies-tresses (Spiranthes spiralis) is one of them, never flowering before August and continuing well into September. This is probably the least conspicuous of the orchids which are found in the Bristol area, typically only reaching about ten centimetres tall. The photos below show the way in which the tiny flowers spiral around the stem, a feature reflected in its scientific name.

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I visited the colony on Bristol Downs today, and counted at least 87 plants – although among these were many which weren’t in full flower yet, which I only noticed when I was on my knees next to plants which were in flower, so as I will have no doubt missed other similar individuals, I’m confident the total population here is well into three figures.

Here’s the location: right next to the circular road which runs around the Downs.

Autumn Ladies-tresses is a plant of very nutrient-poor limestone and chalk grassland. In most locations, sheep do the work of keeping the habitat conditions right; on the Downs, in the absence of sheep, the grassland has to be managed by mowing and raking off the cuttings. On the side of the colony closest to the road, the soil has been badly eroded by runners; fences have been erected to encourage people off of this part of the site, in the hope that it will regenerate.

The Downs as a whole are a bit of a curate’s egg botanically, even if you discount the areas which are formally set aside for sports. Although it is certainly the largest area of limestone grassland around Bristol until you reach the Mendips and Cotswolds, that doesn’t necessarily mean it’s good-quality limestone grassland throughout. Some areas are good – I found a few Harebells (Campanula rotundifolia) growing in another spot today, for example – and the stone workings on the southeast side have some botanical interest, as does the area around the observatory. However, other parts are quite species-poor. With the right management to reduce the nutrient levels, though, the Downs could certainly become a lot richer, and complement their neighbour the Avon Gorge.

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Two scarce riverbank plants

Earlier this month, I took a walk along the River Avon from Conham to Hanham. to check out some of the scarce plants which occur locally in riverbank habitats. The highlight was this Greater Dodder (Cuscuta europaea), a parasite of the Common Nettle (Urtica dioica): the upright green stems are those of the nettle, and the red stems twining around them belong to the dodder.

This is a nationally scarce plant, found in only a handful of areas in southern and central  England. Locally, it occurs in two areas. It is found along the River Avon from Bristol upstream to Bath, and again to the east of Bath into western parts of Wiltshire; its other stronghold is along the River Severn (mainly around Gloucester but with an outlying site near Frampton-on-Severn).

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The closely-related Common Dodder (Cuscuta epithymum) also occurs in our area, and is also a scarce plant, despite its name. It is found in heathland and dry grassland and parasitises among other things, species of gorse, heather and thyme. It has smaller flowers, although to be certain of the identity of a dodder specimen, a flower has to be dissected under a microscope, to look at tiny features such as the shape of the minute scales at the base of the inner surface of the flower and the relative length of the sex organs.

Here’s the area where I found the plant photographed above:

Also present in good numbers throughout this section of the Avon was Small Teasel (Dipsacus pilosus), the scarce relative of the ubiquitous Common Teasel (Dipsacus fullonum). In and around Bristol, it is found on the River Avon between Bristol to Bath, on the River Frome in northeast Bristol, on the River Chew, and scattered other localities, often in or on the edge of woodland.

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Roesel’s Bush-cricket

It’s the time of year when orthopterans are out in force just about anywhere with any decent vegetation. There are four families represented in Britain: grasshoppers are common and familiar; the larger bush-crickets (which many people just refer to as “crickets”) are less conspicuous but still common; then there are the groundhoppers, which take a bit of searching for, and the true crickets, which are just downright rare. This diversity is the reason for going ever-so-slightly jargony with that first sentence: there isn’t really a single good shorthand name, the best compromise probably being “Grasshopper and crickets”.

They are quite an easy group to get to grips with, as there are only about 30 species in Britain, and the species featured in Vic Savery’s photos below is an easy one to identify: the long antennae and chunky body are characteristic of a bush-cricket, and the pale crescent around the edge of the side-panels of the thorax are a dead giveaway for Roesel’s Bush-cricket (Metrioptera roeselii).

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Roesel’s Bush-cricket, 12 August 2013, Avonmouth, Bristol, Vic Savery (naturenutz.net)

When the last national Orthoptera atlas was published back in 1997, Roesel’s Bush-cricket was largely confined to the Home Counties, with isolated outlying coastal populations in a few other areas. However, like a number of other species of bush-cricket, its populations have expanded since then, and it now occurs around Bristol. It is well-established in Wiltshire and Gloucestershire and has also spread into Gwent in the last decade. Robert Cropper’s 2011 book “The Orthoptera and allied insects of Somerset” documents surprisingly few Somerset sites: a strong population around Bridgwater possibly marks the southwestern edge of the current British range, although the range expansion is no doubt ongoing, so I’m sure that the species will reach Devon soon if it hasn’t already.

The song of Roesel’s Bush-cricket is a high-pitched buzzing, pitched at around 22 kHz. If like me, your hearing has deteriorated to the point where you can’t hear sounds which are that high-pitched, you’ll need to use an electronic detector to track one down. Vic tells me there were three or four singing at his site, on Kingweston Lane near Avonmouth. In all likelihood there are other sites elsewhere in the city too.