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Wildlife of Marshalls Heath
The total number of plant species (excluding fungi) that have been found growing on the Heath between 1970 and the present now totals 215, comprising 21 species of tree, 32 grasses, ferns and mosses, and 162 flowers. Out of this total, about 20 may be garden escapes, throwouts or plants that have been deliberately planted on the Heath, leaving a natural flora of nearly 200 types of wild plant. This is a diverse flora, considering the tiny area concerned. The first detailed maps of the flora of Hertfordshire were produced by Dony (1967), who lists 257 plant species for the entire TL11s tetrad (2 x 2 km square) in which Marshall's Heath lies. Considering that a tetrad measures nearly 1000 acres (400 hectares) in size, it is extraordinary that four fifths of its total species of flora should be found in an area less than 1% of its size. A new Hertfordshire Flora is being produced by Trevor James, the county recorder, who also works at CEH Monks Wood (Centre for Ecology and Hydrology).
However, despite this rich diversity, it has to be said that the vast majority of the heathland plants are widespread, common species in Herts., and very few of them are unusual or rare. They are important as foodplants on which much rarer insect and therefore bird life depends, however, and this is illustrated in the Rare Species section. It should also be remembered that the flora of an area may change with climate and different land use; 15 of the species found on the Heath since 1970 were not recorded in this tetrad by Dony (1967), and 15 of the plants listed in previous surveys could not be found in the surveys carried out in 1992-1995, despite the extensive searches throughout the year. These plants unfortunately include some of the most interesting and rare species, such as Betony, Squinancywort (possibly an error?), Rough Hawksbeard, Fine-leaved Sheep's Fescue, and Prickly Buckler-fern. The characteristic plant of the heaths of lowland England is heather (Calluna vulgaris), but this had died out at Marshalls Heath before the first flora surveys were carried out, though Vincent Judd, who lived in the area as a boy, remembers where it used to grow in around 1954 to 1958.
The picture on right shows 3 fine oak trees at the south end of the Heath
A list of trees seen at Marshall's Heath is given in the species list section, together with five columns indicating their presence in the six surveys carried out between 1970 and 1995. Three of these, the sycamore, cherry and the wayfaring tree, are known to have been planted, and some, such as the apple trees, were probably planted. The rest, primarily oak and elm, have propagated themselves from the huge trees that used to line the hedges to east and west before the war, and of which half a dozen oaks remain, the elms having died in 1976 to 1977 of Dutch Elm disease. None of the trees on the Heath can be described as anything but common, most occurring throughout Hertfordshire. The least widely distributed is the Crab apple tree, which is found in about half the tetrads of Hertfordshire only.
Grasses, Ferns & Mosses
The 32 species of grass and ferns that have been found growing on the Heath are listed in the species list section. Notes of their use as butterfly food plants are also included, as an illustration of the interdependence of one species on another exhibited by all fauna in an ecosystem. Half of the grasses are used as foodplants by at least one species of butterfly resident on the Heath, and so form a vital link in the food chain on which the wildlife of the Heath depends.
Four of the grasses and ferns listed in the species list section can be classed as rare: Velvet Bent-grass and the Prickly Buckler-fern, which are found in only 5% of the tetrads (2 x 2 km squares) in Hertfordshire, Fine-leaved Sheep's Fescue, which is found in only 11/2% of the Herts. tetrads, according to Dony (1967), and the Western Scaly Male Fern, the rarest plant on the Heath, which is known from only one other locality in Hertfordshire, though being comparatively recently distinguished as a separate species, it may be under-recorded. Fine-leaved Sheep's Fescue is a type of grass found on acid heaths that has suffered enormously from the 96% decline in heathland in Hertfordshire since the war.
Altogether, 162 species of flower have been recorded at one time or another on the Heath; these are all listed in the species list section. 11 of these are virtually certainly garden escapes, throwouts or deliberately planted, and another 10 possibly are. Most of the remaining wild flowers are common in Hertfordshire, but 2 are rare and merit special attention: Squinancywort (Asperula Cynanchica) which is found in only 17 of the 462 tetrads in Herts. (i.e. less than 4% of tetrads) was recorded in 1984, but is probably an error. Rough Hawksbeard (Crepis biennis) is found in only 13 other tetrads, or 3% of the total (Dony 1967). Unusual plants are Wood Groundsel, Common Comfrey, Heath Bedstraw, Russian Comfrey, Heath Speedwell and Betony, which are found in 13%, 16%, 18%, 21%, 23% and 25% of Hertfordshire tetrads respectively. Of the remaining hundred or so species listed in the species list section, all were found in more than one third of Hertfordshire tetrads before 1967, but at least five species are now declining: the Harebell (Campanula rotundifolia), Pignut (Conopodium majus), Lady's Bedstraw (Galium verum), Tormentil (Potentilla erecta), Barren Strawberry (Potentilla sterilis) and Orpine (Sedum telephium). Two further species of interest, Betony and Heath Speedwell, which were not seen in 1992-5 but were recorded in earlier surveys, may reappear again.
Despite their common occurrence, ten flowers are important as foodplants for butterflies found on the Heath, and many more are foodplants for rare moths and other insects.
Mammals, Amphibians and reptiles
At least nineteen species of mammals, two amphibians and two reptiles have been seen on the Heath or its immediate vicinity, and thirteen of the mammals definitely or probably breed there. No systematic study has been undertaken, but casual observations by the author since 1976 have been summarised in the species list section. Bats are a regular and spectacular sight swooping and turning after insects on warm summer nights, and have been identified as Pipestrelle Bats from their flight patterns. Other species may be present as well, perhaps the Noctule and Brown long-eared bats. All of the mammals and amphibians are reasonably common in Hertfordshire and southern England generally, but the Common Lizard is becoming increasingly rare in Hertfordshire, and any site supporting it is of value. It feeds upon adult and larval insects, centipedes, spiders, snails and earthworms, and requires a mixture of cover for it to hide and open spots for basking, all of which are found on the Heath. The Grass Snake has unfortunately not been seen since about 1958, when Vincent Judd saw it on the Heath very occasionally. Picture of vole shown above and on right, the Common Lizard, photographed in Hertfordshire in 2002.
The 71 different birds noted on Marshalls Heath or its immediate surroundings are listed in the species list section, which also includes information on whether the bird was seen flying over or settling, together with its breeding status on the Heath. The latter is divided into three categories of certainty as defined by Gladwin & Sage in their 1986 book on the birds of Hertfordshire: ?? indicates possibly breeding, which means that the bird has been seen on the Heath in the breeding season, but no further evidence of breeding exists. ? means probably breeding, where the species has been seen in a likely breeding habitat at the right time, and is showing evidence of breeding behaviour such as defending territory or persistently singing. v indicates definitely breeding, i.e. a nest or eggs have been found, or parents feeding young birds have been seen.
Again no systematic study of birds on the Heath has been carried out, but the residents have noted down species that they were able to recognise from time to time. Michael Beedell and Mark Kingett regularly noted the nesting birds, and erected and maintained many nesting boxes, but have now moved away from the district. The nest boxes have been occasionally checked since by Peter Wilkinson, who has also identified some birds new to the Heath by their song. Mike Russell has agreed to pay visits to the Heath this year, but if you are interested and can recognise birds or are willing to learn, please contact John Murray on firstname.lastname@example.org
Of the 71 species of birds, 19 may be breeding there, and 22 definitely are. Many of the suspected or definite breeding birds are common residents of Hertfordshire, but a lot of these are declining, some of them seriously. Nine birds of Marshalls Heath are now on the RSPB Red List, and a further 10 on the Amber List. Details are given in the Rare and threatened species section. Green Woodpecker, very frequently seen on the Heath, has been a fairly scarce declining resident but is now thankfully recovering, though it is still on the Amber List. Both the Grey Partridge and the Sparrowhawk are recovering from a significant decline caused by the widespread use of pesticides in the 1950s and early 1960s which brought the latter to the verge of extinction in southeast England. The Red Kite was exceptionally rare but an introduction programme has greatly helped this bird. One was spotted flying north at a great height over the Heath, being mobbed by Crows as it went, by Georgina Beedell in 1991, and another by Mike Russell in 2000.
Marshalls Heath is too small to be attractive to many unusual species, and the nesting behaviour of some leaves them vulnerable to dogs, which are often let off the lead when being walked across the Heath by their owners. Regarding the management of the Heath, generally speaking what is good for the insects will be good for the birds, but some species will benefit from good thick undergrowth for protection, so it is important to leave some scrub and thicket at the edge of the heathland. The woodpeckers, particularly the Green Woodpecker, are probably attracted to the Heath by the ants and other insects, so good maintenance and extension of the present heathland will benefit them. For nesting they require dead wood, as their beaks are not strong enough to hollow out live trees, so dead trees should be left standing, particularly large ones, where it is safe to do so.
Butterflies are the fastest disappearing group of animals in Europe, so special attention should always be paid to their conservation. Nowhere is this decline so desperate as in Hertfordshire, where nine species of butterfly have become extinct since the war, and a further five survive in one area only with very low numbers. This is out of a total of 46 resident breeding species before the war, so in other words, one third of Hertfordshire's butterflies are now extinct or virtually so.
Altogether, 29 different species of butterfly have been seen at Marshall's Heath, a high total considering the tiny area concerned. Three of them have not been seen for more than eight years, and are presumed to be locally extinct. 15 of them probably breed there, and a further 10 possibly do. A full list is given in the species list section. 18 of the listed species are fairly common to abundant in Hertfordshire, but eight have shown declining numbers, and six are rare or rather scarce.
Nearly all of the butterflies live on the heathland, where the foodplants on which they lay their eggs grow. Some species found on the heath are extremely sedentary, and will not stray more than 30 yards or so during their entire lives. Butterflies are subject to wild fluctuations in numbers, and so sedentary species are particularly vulnerable when conditions deteriorate, as they cannot or do not fly elsewhere to colonize new areas. Three rarer species, all of which can (and probably do) breed on the Heath are singled out for special attention. They are the Brown Argus, the White-letter Hairstreak, and the Small Heath.
A small colony of Brown Argus was discovered on the Heath in 1991, and it has been recorded each year since. This is a sedentary species of butterfly, and easily confused with the female Common Blue at first glance, so it is probable that it was overlooked in previous years. It is a declining species in England. Its main foodplant is Rock-rose, though here it may be using Dove's-foot or Cut-leaved Cranesbill. These plants are easily shaded out by tall grass, so this butterfly requires short grass to survive. The caterpillar has a symbiotic relationship with ants. It has special honey-glands and microscopic pores which exude sweet, sticky droplets that ants find irresistible. Like the caterpillars of other Lycaenid butterflies, it probably "sings" to its attendant ants by rasping segments of its body together. In return, the ants ferociously guard the caterpillar against other species of carniverous ants and wood wasps. It is also probable that ants attend and protect the pupa in the same way.
White-letter Hairstreak was also found on the Heath in 1991, and has been seen in most years since. This is an elusive butterfly that is easily missed, as it spends almost its entire life in the tree tops, tumbling and circling in the sunlight or feeding on honeydew, only occasionally descending to feed on privet or thistle. The caterpillar feeds on elm, which is still abundant on the Heath, so it is likely that a small colony survives here. The female lays eggs at all heights on elm trees, where the caterpillars feed and eventually pupate. The pupa, like other Lycaenid butterflies, possesses a sound organ , and can emit a curious rasping song. It is likely that this pupa attracts ants, though no one has confirmed this. A dramatic decline in the White-letter Hairstreak has occurred in the last 20 years. Dutch Elm disease has decimated woods in England and a large number of White-letter Hairstreak colonies have disappeared as a result. It has been classed as a Nationally Notable (Nb) species, and is also in Butterfly Conservation's Regional Action Plan as a Biodiversity Action Plan (BAP) species. Preserving the colony at Marshall's Heath is a top priority.
The Small Heath butterfly used to be common everywhere, but has declined recently and disappeared from many sites in Hertfordshire. As its name suggests, it thrives on heathland and the well-grazed vegetation that used to be a characteristic of them, and at Marshalls Heath its numbers built up during the hot summers of the mid-1990s. It has since declined as brambles and scrub have encroached and the grassland on the Heath has become rank and overgrown, and was last seen here in 1999. Bramble removal and heathland restoration may allow this species to return.
Finally, a note on some of the species that are gone from the Heath. The Green Hairstreak, a localised species that is declining in numbers everywhere, was seen at the edge of the woodland at Marshall's Heath in 1987 by M.Beedell, but has not been seen since. The caterpillars feed on a variety of foodplants; here it probably uses Bramble, or possibly Common Vetch or Bird's foot trefoil. Females are very fussy about the quality of the plant they lay their eggs on, choosing only the tenderest young shoots which contain the most nitrogen. They pupate inside ant's nests, which probably explains both their presence on the Heath and their general decline elsewhere. They require a warm and sheltered site with plenty of shrubs, and it is probable that throughout the 1980s they used the narrow strip of shrubbery to the west of the road and north of the anthills, near where they were last seen, before this became overgrown.
The Wall butterfly suffered a catastrophic decline and extinction in most of Hertfordshire between 1990 and 1996. The reasons for this decline are unknown, but it was particularly marked at Marshalls Heath, where more than a hundred were recorded in 1990, declining to only 5 seen in 1995, and none since. It is a sobering lesson on the fragility of wildlife and the limits of our present knowledge.
The White Admiral was very occasionally seen in the 1950s by Vincent Judd, but has not been seen since. This butterfly seems to be extending its range at the moment, and has turned up in Harpenden, Welwyn Garden City and Hemel Hempstead, so it is possible that it may return. Certainly its caterpillar foodplant, Honeysuckle, is common enough on the Heath.
The Marbled White butterfly was seen on the Heath in 1991 and 1997. It is one of the few signs of hope among English butterflies, in that it is one of three or four British species that appears to be presently increasing its range. It was regarded as extinct in Hertfordshire in the early years of this century. Then, particularly during the series of warm summers of the 1940s, the butterfly reappeared at Tring in the west of the county, re-colonising it from strongholds further west in Buckinghamshire. Poor summers in the 1950s and 1960s all but caused its disappearance again, but since the 1970s, it has re-established itself in the west of the county, and has been spreading east across the county ever since. Its appearance at Marshall's Heath in 1991 may well have been the first this century. It feeds on several species of grass, particularly sheep's fescue. On the Heath it will hopefully be attracted by the cock's-foot and red fescue. Unlike the Brown Argus it requires long, lush grass for its habitat, and is easily exterminated by over-grazing.
The picture on the right shows Pale Tussock moth, May 2002.
Moths have been systematically studied by the use of a moth trap since 1993, and records are summarised in the species list section. It is clear that Marshalls Heath is a quite exceptional locality for moths, with 667 species seen altogether, the highest total for any site in Hertfordshire. Among them are 22 moths that are nationally rare, endangered or local, and 9 moths that are not found elsewhere in Hertfordshire. These are summarised in the Rare and threatened species section. Pictures of many of these can be seen on the UK Moths home page.
The Heath is host to a great diversity of insect species, though little work has been done on them. Two insects in particular attract attention.
The Yellow Hill Ant (Lasius flavus) is responsible for the anthills on the western side of the road. Although the Yellow Hill Ant is a common insect which can be found on any patch of wild grassland, it is unusual to find such large anthills, and the Heath has one of the finest colonies of this insect in Hertfordshire. The anthills are probably all part of the same community that grew so large that it needed to spread. Each anthill will contain a number of queens, and the population may be in the hundreds of thousands. They have no sting, though they are capable of nipping the skin with their powerful jaws. Two other ant species, Myrmica scabrinodis and Myrmica ruginodis, were noted by P. Attewell, Herts. recorder for ants, during a visit on 1992 Sep. 19th, and the Jet Ant (Lasius fuliginosus) was found here by John Widgery in August 1995.
Glow worms (Lampyris noctiluca)are an attractive feature of the Heath on summer nights, when dozens of them may be seen in the long grass and the thickets at the edge. Despite their name and appearance, they are beetles, but the female has a segmented body, though the male does not and looks like an ordinary beetle. Although still found in many places, there is strong anecdotal evidence that glow worms were once much more common in England than they are now, and many colonies have disappeared. They have an interesting lifestyle in that they are carnivorous, and both the adult and the larvae feed on snails by injecting substances into the snail's body that first paralyse and then dissolve it. The glow worm then feeds on the snail until the shell is empty. The growth period is long, and the larvae may live for two or three years before changing into an adult. Only the female emits the pale greenish light, which is used to attract the males, which have large eyes to detect the pinpricks of light. The females sometimes climb grass stems so that they can be found more easily.
There is evidence that standing lights are partly responsible for the decline in glow worms, as they may attract and disturb the males and so leave the females unmated. The Sodium vapour street light at the south end of the Heath may have affected the glow worms.
Glow worms prefer open unimproved grassland, i.e. unsown grassland not drained or treated with herbicides or pesticides like most sheep pasture nowadays. They require sufficient snails in order to survive, so their survival depends on maintaining areas of unkempt woodland floor with vegetable refuse for snails to live and breed. They have suffered enormously from the general "tidying up" of the countryside since the war.
Though not systematically studied, more than 70 beetles have been identified by Trevor James, the Hertfordshire Natural History Society recorder for beetles. Among these are some nationally scarce or nationally notable species, and one, the Monks Wood Beetle (Hallomenus binotatus) that does not occur anywhere else in Hertfordshire. This beetle feeds on fungi that grows on old trees, and many of the rare beetles depend on dead or rotting wood for their survival. An important part of good woodland management is to leave fallen trees and branches where they are, because the wood becomes a food source for a great variety of insect life as it rots down, which in turn provides food for many woodland birds. The E.E.C. have become so concerned at the reduction in dead wood habitat due to the modern habit of removing and burning dead wood from forests that a special recommendation (number R(88) 10) has been issued to try and discourage the practice.
Other uncommon species include Serica brunnea, Chrysolina oricalcia and Stenagostus rhombeus (8 trapped in 1994) which has only been seen in east Hertfordshire before. Ptinus sexpunctatus is a nationally notable species, though it appears to be not unusual in Herts. A most unusual capture is Cantharis figurata, which has only been recorded 3 times before in Hertfordshire, the last time in 1954. Agapanthia villosoviridescens was uncommon but has increased its numbers recently. Among the common species, Bradycellus verbasci appears in huge numbers on some nights in July and August. The Sexton beetles, Nicrophorus humator & Nicrophorus investigator are found regularly each year, as is Aphodius rufipes.
About half a dozen different species of dragonfly regularly patrol the Heath in late summer, some new ones having been identified by Trevor Chapman.
These frequently turn up in the moth trap, and some of these have recently been identified by Veronica Edmonds-Brown, the Hertfordshire recorder for Caddis flies. 25 species have been found, including Rhycacophila dorsalis, a regionally notable species. Britain's largest Caddis fly, Phryganea grandis, is occasionally recorded here.
Bees and Wasps
Raymond Uffen, the H.N.H.S. recorder for bees and wasps, visited the Heath in 1995 and identified many solitary bees, sawflies, ichneumons and wasps. The total number of species now stands at 41, and includes the first ever record of the Homeless Bee Nomada panzeri in Hertfordshire. Another species rare in Hertfordshire is the Large Spurred Digger Wasp (Nysson spinosus), found exploring the roadside ditch bordering the northern woodland clearing on 12th July 1995. Among the different species of wood wasps recorded here is the spectacular Greater Horntail (Uroceras gigas).
Very poorly studied, only 50 or so species have been positively identified, though a further 20 species await confirmation. Ian Wynne and Raymond Uffen have identified many hoverflies, and several species of cranefly are regularly found. It is hoped that trials with a Malaise trap this year may improve this total.
Grasshoppers, crickets and bugs
John Widgery, the Hertfordshire Natural History Society recorder for these insects, visited the Heath in 1995, and has since identified other bugs found by John Murray. 8 grasshopper and cricket species, together with 31 species of bug are now known to occur here, listed in the species lists section. Roesel's Bush-cricket (Metrioptera roeselii), the Oak Bush-cricket (Meconema thalassinum), Dark Bush-cricket (Pholidoptera griseaptera) and the Speckled Bush-cricket (Leptophyes punctatissima) are popular creatures of the late summer.
Finally, many other types of insect have been found here: bristletails, mayflies, thrips, lacewings, snake flies and scorpion flies.
Spiders have really not been studied at all, and there are very few records of millipedes, woodlice, harvestmen and worms. John Murray has looked at some slugs and snails, and 12 species have been tentatively identified. Not the most popular form of wildlife, but these garden pests are important for the rather more popular glow worms mentioned above.
Updated 27 Feb 2003