Page 1

4

Suffolk Natural History, Vol. 39

SUFFOLK GRASSLAND AS A BUTTERFLY HABITAT ROB PARKER Grasses (Poaceae) provide the larval food of almost a third of British butterflies, and of 10 of those breeding in Suffolk. All the butterflies concerned are brown in colour, and they belong to the families Satyridae (the Browns) and Hesperiidae (the Skippers). Yet individual species are selective; not every grass will do. Established records of which larvae will eat which species of grass are not always dependable. Some are too generalised, some record grasses accepted in captivity which would not have been chosen in the wild, the worst could be based on observations made years ago, possibly in a foreign land, and perpetuated without confirmation. Given the loss of grassland in Suffolk, and the changing distribution of some of the butterfly species, it seems worth matching butterflies to specific grass species, if only to see whether any pattern emerges in host plant exploitation. The Semantics of Larval Host Plants (LHPs) The plant eaten by larvae may properly be described as the Larval Host Plant, and abbreviated to LHP. Although most popular entomological textbooks use the convenient expression “foodplant”, no such word is to be found in dictionaries or in biological encyclopaedia, though foodstuff generally is listed. Pabulum is Latin for food, and is also in regular use by some entomologists to mean the food of caterpillars. This paper nonetheless follows Asher et al., (2001) in using the familiar “foodplant”. Grass Species Simpson (1982) lists some 139 grasses found in Suffolk, a 100 of which are native species. Many of these have more than one vernacular name, not all of which are helpful in identification. Some are common, and are considered to be palatable to the caterpillars of many butterfly species (Bink, 1985), whereas others are scarce or local, yet favoured by certain butterflies. Only 32 of these grasses are noted in the entomological literature as foodplants of any of the 10 butterfly species. Typically, matches will occur where a particular biotope hosting a particular grass community also suits a particular butterfly. For example, Graylings are found on the sandy soils of the Sandlings and on the coast, where Marram grows and serves as one of several foodplants for the butterfly. Marram has not been recorded as the foodplant of any of the other 9 butterflies. On the other hand, Cock’s-foot suits 8 different butterfly species, and Yorkshire-fog suits 5. It is certain that many entomologists recognise Cock’s-foot and Yorkshire-fog, but are unfamiliar with more obscure grasses, so there is an inevitable recorder bias. Table 1 below lists only the 32 grass species that have attracted records. They are presented in the same sequence used by Simpson (1982), but updated with the scientific and vernacular names used in New Flora of the British Isles (Stace, 1997). Sedges are not grasses, and have not been included, even though the Ringlet caterpillar has been known to eat Wood-sedge and other Carex species. Grass species not found in Suffolk have been excluded, even those known to suit some butterflies found in the county.

Trans. Suffolk Nat. Soc. 39 (2003)


GRASSLAND AS A BUTTERFLY HABITAT

5

The nature of a caterpillar’s life-cycle suggests that perennial grasses will be selected in preference to annuals, and this is indeed the case. Approximately 30% of our grasses are annuals, yet only one, Annual Meadow-grass, has been recorded as a foodplant, and this is properly described as “an annual or short-lived perennial” Hubbard, 1984. Butterfly Species and Foodplant Literature Seven separate works of reference were consulted to establish the larval foodplant preferences for the 10 butterfly species. In general, there was reasonable agreement, particularly concerning which of the common grasses is most frequently selected in the wild. There was also sufficient difference between books to feel that authors had some personal experience, and were not merely reiterating earlier records. Regrettably, at this stage, the records do not all come from Suffolk, but from a broader base, mostly from England. Each book has its own qualities, and is referenced in Table 1 by the use of the following numbers: 1. A Field Guide to Caterpillars of Britain & Europe. (Carter & Hargreaves, 1986). Authoritative, but at genus rather than species level. 2. The Millennium Atlas of Butterflies in Britain & Ireland. (Asher et al., 2001). Firm data at species level, mostly derived from Thomas & Lewington, concise. 3. Butterflies of Britain & Europe. (Tolman & Lewington, 1997). Comprehensive listing at species level, but partially derived from European data. Well-researched, using “sources deemed to be reliable” and assistance from many professional botanists. 4. Caterpillars of the British Isles. (Porter, 1997). Records a number of grasses not included in other books, possibly reflecting extra foodplants accepted in captivity. 5. The Butterflies of Britain & Ireland. (Thomas & Lewington, 1991). Overall, the most helpful, with many excellent observations, sometimes including grasses rejected. Not quite comprehensive at species level. Probably the source of some of the entries in later books. 6. The Butterflies of Suffolk. (Mendel & Piotrowski 1986). Generalises somewhat, adding useful detail about habitat in Suffolk. 7. Butterfly Lives. (Beaufoy, 1947). Detailed observations from Suffolk, with excellent photographs of early stages, but only for the Wall and Grayling. Note that the numbers above have only been included on the table for grasses identified to species rather than genera. In all, 17 British butterfly species (out of 60 or so) are grass feeders. Those not found in Suffolk have been excluded from the tables below. For the record, these are: Silver-spotted Skipper, Chequered Skipper, Lulworth Skipper, Mountain Ringlet, Scotch Argus, Marbled White and Large Heath. Ongoing work by Dennis & Shreeve seeks to refine the national database of larval host plants, but is complex and beyond the scope of this paper.

Trans. Suffolk Nat. Soc. 39 (2003)


6

Suffolk Natural History, Vol. 39

Trans. Suffolk Nat. Soc. 39 (2003)


GRASSLAND AS A BUTTERFLY HABITAT

7

32 Grass species, plus sedges for Ringlet. The most generally palatable grass would appear to be Cocks-foot, which suits 8 species out of 10. Notes: [1] Scientific name changed from that used in the entomological literature. [2] Includes A. vinealis, Brown Bent. [3] Includes P. bertolonii, Smaller Cat’s -tail

Larval Foodplant of Choice Table 1 shows that some grasses are popular for most species, with Cock’sfoot suiting 8 species, and False Brome serving 7. On the other hand, there are 3 genera of grass for which only one butterfly is a registered customer – Arrhenatherum is eaten only by Ringlet larvae, Ammophila by Grayling, and Nardus by Small Heath. Equally, some butterflies are less choosy than others. The Ringlet caterpillar will eat 16 species and Meadow Brown 13 or so, whilst the Skippers stick to 5 or 6 preferred grasses. None of Suffolk’s butterfly species are totally dependent on a single grass species, though this situation can prevail with rare species elsewhere, e.g. Chequered Skipper (Purple Moorgrass) and Lulworth Skipper (Tor-grass). It is unsurprising that those species able to adapt to the available grasses are the generalist survivors, whilst the specialists struggle and become rarities. Table 2 incorporates more detail on the characteristics of each grass, its status in Suffolk, and the associated habitat. In 3 cases, taxonomic changes have split the species generally cited in entomological literature, so it has been necessary to tabulate both the “parent” species and the related species. These are: Festuca ovina plus F. filiformis, Agrostis canina plus A. vinealis, and Phleum pratensis plus P. bertolonii. It has been assumed that butterfly larvae that eat one will accept the other. Indeed, it seems likely that Gatekeepers and Meadow Browns would feed on A. vinealis in preference to A. canina which grows in situations liable to innundation. Equally, P. pratense in Suffolk is an infrequent escape from cultivation, and the Skippers recorded from “Timothy” are more likely to feed on P. bertolonii (Smaller Cat’s-tail) in the wild. The splitting of names is not really very recent, since Simpson (1982) recognises all 6 taxa, though under different names, and the difficulty arises from the use of unspecific vernacular names in the entomological literature. Suffolk Grasslands Post-war agriculture has led to the loss of most of Suffolk’s semi-natural grassland, and fragmented much of the residual high quality grassland to the point that the Local Biodiversity Action Plan includes the habitat action plans listed below. Nonetheless, some good grasslands remain, for example Wortham Ling, where 44 grass species support at least 8 of the grass feeding butterflies. National Vegetation Classification (N.V.C.) labels exist to describe the plant communities involved (Rodwell, 1992) and these are mentioned where relevant. Most fall into the Mesotrophic Grassland categories of MG1 to 12, however, these definitions are of limited value in judging butterfly associations. Most butterflies frequent several overlapping biotopes, although some do favour specific conditions which match particular grassland types.

Trans. Suffolk Nat. Soc. 39 (2003)


Bromopsis erecta Brachypodium sylvaticum pinnatum Elytrigia repens Festuca arundinacea ovina filiformis rubra pratensis Lolium perenne Poa nemoralis annua pratensis trivialis Dactylis glomerata Cynosurus cristatus Arrhenatherum elatius

Species

“Twitch”, arable and roadside weed Meadows, aggressive coloniser of verges Local, often dominant on poor acid soils Local of poor acid soils Sown for sports-grounds etc Local to rare; waysides, ancient pasture In garden lawn mixes Common, waysides, resown leys. Woodland & margins Weed of disturbed ground Hay pastures, grazing, road verges Copses, shady places with rank vegetation Common, widespread A major feature of traditional meadows Abundant, especially on verges

Broad-leaved, coarse Fine, short, compact Fine-leaved, like. ovina Fine Broad-leaved Rye-grasses often cultivated Native

Narrow, flat blades Broad-bladed, soft Rather stiff, hairless Leaves weak, flaccid

Broad-bladed, Coarse , Tall

Coarse

Coarse, tall

Woodland, scrub & hedges Rare or local on chalk

Tall, often dominant

Very variable, related to wheat Broad-bladed

Local on chalky heaths

Status/Habitat

Tall, soft perennial

Characteristics

Table 2. CHARACTERISTICS OF GRASSES SERVING AS LARVAL FOODPLANTS 35 Grasses arranged as in Simpson’s Flora of Suffolk. (Nomenclature follows Stace, 1997)

ss

ss

es

es

es es

ls

ls ls

Trans. Suffolk Nat. Soc. 39 (2003) sw w

sw w

sw w

sw w sw w

mb

gk

gk gr gk mb mb gk

gk

mb gr gk mb gr gk mb gr gk mb gk

gr gk mb

gr

mb

Caterpillars eating this grass

r

r

r

r

r

r

r

r

r

sh

sh

sh

sh sh sh

8 Suffolk Natural History, Vol. 39


Abundant Local, often plentiful on heathland Common in damp meadows Woodland, under shade Occasional on heaths, drier parts of fens Local on sand dunes V. common, heaths and acid pasture Common weed on recently disturbed soils On damp acid heaths On dry heaths Common in damp pasture, verges Cultivated, and escape Common native Common, damp ground Rare, acid heaths

Soft Soft

Short, early flowering

Coarse

Coarse, tall, invasive

Leaves, rolled, rhizomes in sand

Leaves narrow, flat. Rhizomatous Robust and coarse Like Common Bent Taxon split from A. canina Stoloniferous on surface

Coarse Taxon split from P. pratense

Early flowering

Densely tufted

Large tussocks,. Late to start (May) Local, heaths & fens

Local, Dry heath, banks Damp pasture, especially on clay

Not tussocky Coarse, Tall, “Tussock grass�

Notes: Italics: denote judgement that caterpillars are less particular about nomenclature than botanists. Bold: indicates favourite choice (Not all species have a favourite).

Deschampsia flexuosa cespitosa Holcus lanatus mollis Anthoxanthum odoratum Milium effusum Calamagrostis epigejos Ammophila arenaria Agrostis capillaris gigantea canina vinealis stolonifera Phleum pratense bertolonii Alopecurus pratensis Nardus stricta Molinia caerulea ss

ss ss

ss ss

es es

es

ls

ls

w sw w

sw w

w

gr

gr

gk gk mb

gk mb gk mb mb

gk

mb

mb

r

r r

r

r

r r

r

sh

sh

GRASSLAND AS A BUTTERFLY HABITAT

9

Trans. Suffolk Nat. Soc. 39 (2003)


10

Suffolk Natural History, Vol. 39

Lowland Hay Meadows (N.V.C. MG4 &5) Old meadows, or “unimproved grasslands” are the typical botanically rich hay meadows of yesteryear, 97% of which have been lost over the past 50 years. The fragments that remain are spread across Suffolk Coast & Heaths, The Broads, the East Anglian Plain, and Breckland, and they invariably support most of the grass feeding butterfly species. Note, however, that low cutting will kill many larvae, and populations will be strongest in meadows with areas that have remained uncut for several years. MG5 is described as CentaureoCynosurion grassland, mown annually for hay, grazed in autumn/winter and manured by stock (as is MG4, which differs in being flooded in winter). Lowland Dry Acid Grassland (N.V.C. U1) The B.A.P. includes all the acid grassland which occurs as an integral part of the Sandlings and Breckland heathland. On nutrient-poor sandy soil, it is characterised by a plant community dominated by Sheep’s-fescue, Sheep’s Sorrel and Common Bent, with Sand Sedge and Wavy Hair-grass sometimes present too. Many of the invertebrates occurring in acid grassland are not found elsewhere. The Grayling breeds almost exclusively in this habitat. The Wall and Small Heath are also both more at home here than in meadows. Lowland Wood Pastures & Parkland (N.V.C. W10/W16) Lowland wood pasture and parkland are both products of historic land management, and are likely to comprise ancient oaks set in unimproved grassland, often offering the continuity of habitat so rare in our agricultural landscape. Sites such as Staverton Thicks and Aspal Close maintain strong populations of Browns and Skippers, largely because they have escaped the plough and pesticide sprays. Uncropped areas are best, followed by lightly grazed grassland, with mown parkland supporting fewer butterflies. Such sites were quickly colonised by Speckled Woods during their advance across East Anglia. Fens and Lowland Heath Other B.A.P. habitats support a rich butterfly fauna too; the grass in places like Pashford Poors Fen and our heather heathland provide extreme damp and dry habitats that are important despite being outside the specifically grassland classifications. Some grassland types not listed in the Biodiversity Action Plan also deserve mention: Agriculturally Improved Grassland (N.V.C. MG7) The N.V.C. for agriculturally improved grassland is generally MG7 (Lolium perenne), which is pretty dull stuff and hosts few butterflies (only the larva of the Gatekeeper is recorded to eat Lolium). Sports fields & lawns are even worse. Semi-improved Grassland (N.V.C. MG6) Lolium-Cynosuretum is semi-improved, chemically fertilised and often resown, but can be interesting floristically, encouraging some butterflies to stay, particularly if some areas remain ungrazed.

Trans. Suffolk Nat. Soc. 39 (2003)


GRASSLAND AS A BUTTERFLY HABITAT

11

Roadside Verges Some of our roadside verges, both protected and unprotected, diverse communities with decent butterfly populations. In some places, verges approximate to N.V.C. MG1 Arrhenatherum elatius grassland, an alliance of ungrazed coarse swards, mown for amenity. Arable Field Margins Conservation margins to agricultural land are being created and extended under Countryside Stewardship and other agri-environment schemes. Our common butterflies are able to exploit this new resource, particularly where the right grasses are planted, and good numbers of Meadow Browns, Gatekeepers and Ringlets generally appear in the second season. Chalk Grassland (N.V.C. CG1 to 8) Suffolk lacks chalk downland, but some of the chalky areas in the Newmarket area and in Breckland do support healthy wild flower populations, and good numbers of butterflies fly in places like Moulton churchyard, the Devil’s Dyke and around the chalk outcrops in the Brecks. Butterfly Preferences and Life-cycle Eggs are laid on specific grasses, so the female butterfly makes the initial choice of foodplant, and it would be unusual for the larva to move to a different grass. Visual clues to biotope, microclimate and grass appearance are normally confirmed by landing on the stem and using chemo-detectors in the feet to confirm host plant suitability. The eggs, singly or in batches, are then laid in a precise place suited to larval needs, usually at the point where fresh blades are about to emerge. Eggs sometimes fall to the ground, and the Ringlet is very imprecise, laying eggs loose from a perch, or even from flight. In these cases, the larvae may have a measure of choice, but may also fail to reach suitable growth. Eggs are often laid on the inflorescence by the Wall, and invariably low down into the sheath by the Small and Essex Skippers. This is important for the Essex Skipper, which will overwinter as an egg, not emerging until the grass makes its spring growth. Larvae of most other species hatch in autumn, feed a little, select a hibernation site well down a tussock, or wrapped inside a curled blade of grass. Inert, they face rain, flooding, frost and snow as tiny caterpillars, yet many survive and are ready to begin feeding as soon as fresh grass begins to grow. Grass is not easily digested, and typically two months are spent feeding up before pupation. Most feeding is done at night, with the larvae climbing tall stems to eat the fresh growth, and retreating down the stem to hide from predators by day. In general terms, leaf eating insects consume from 50 to 150% of their dry body mass per day (Schowalter, 2000). In a Mediterranean climate, the short growing season for grass obliges the single-brooded Browns to pass the long, hot summers in partial aestivation, whereas Suffolk’s longer growing season gives ample time for larval development, followed by a shorter summer flight period. Because the genus has a robust physiology, some are capable of flying until the end of September.

Trans. Suffolk Nat. Soc. 39 (2003)


12

Suffolk Natural History, Vol. 39

The 3 Skippers are all single-brooded, as are most of the Browns, but the Small Heath, Wall Brown, and Speckled Wood all have more complicated cycles which result in flight over a protracted period. In Suffolk, the Small Heath has staggered emergences and a second brood, the Wall is usually double-brooded, whereas the Speckled Wood is unusual in passing the winter in either the larval or pupal stage, resulting in a staggered start to the next season, with up to 3 broods to keep it on the wing from March to October. By the end of the season, the eggs and young larvae are settled into protective clumps of their chosen grass. As can be seen from Table 1, the Skippers are more precise in their choice of grass than the Browns, making them rather more local, though both the Small and Essex Skippers can be abundant in the right habitat. The commoner Browns are very flexible in their choice of grass, Meadow Browns, Gatekeepers and Ringlets being found in practically every tetrad of the county (Stewart, 2001). The remainder deserve individual mention. Grayling The Grayling has declined in recent years, and is becoming more coastal, though our Breckland and Sandlings populations remain strong. Individual sightings in other parts of Suffolk represent wandering butterflies, rather than a multitude of colonies. Wild biotope on sandy, acid soil is a more critical requirement than any particular grass. Wall The Wall is declining in a similar way, and recent records have been sparse, for what used to be considered a widespread and common butterfly. Its taste in grass is not a limiting factor, and its present difficulties are not wellunderstood. It is apparently content across Suffolk Coast & Heaths, but rarely appears in gardens in the middle of the county any longer. Small Heath A similar taste for sandy places marks the present distribution of the Small Heath, which is a more common butterfly on a national scale, but also one which is absent from much of our agricultural clay areas, and is less abundant than it used to be. Indeed, national figures show an annual decline of 4·5%, amounting to a 35% loss over the past decade. Its preferred grasses are Sheep’s-fescue and Red Fescue, which remain in undisturbed heathland, but are declining overall. Speckled Wood On the other hand, the Speckled Wood is a butterfly which has extended its range recently, both across Suffolk, and throughout the whole of Britain. It seems likely that the underlying reason is climate change, with the availability of suitable habitat being a contributory factor (Hill et al., 1999). This exercise has shown it to use 7 grass species, but it seems less dependent on precise woodland habitat than used to be the case, and it would be interesting to discover whether it has also broadened its taste to accept a wider range of grasses. See also Shreeve, 1986.

Trans. Suffolk Nat. Soc. 39 (2003)


Habitat

Eggs Laid

batches in leaf sheath Cock's-foot batches in leaf sheath Cock's-foot in sheltered situation singly under blade Isolated plants in sun in spring, or in singly shade in midsummer on blade/inflorescence Tussocks beneath hedges singly on blade Fine grasses in sand; Sheep's-fescue singly on plants in full sun Fine grasses, esp.bents, fescues & Poa on tall grass or vegetation nearby Fine grasses: Poa, bents on grass or wide range of other grasses too nearby yegetation Coarser grasses, feeding on tall dropped from lush growth stem or flight Short fine grasses: fescues on leaves of fine Feed by day, in sun grasses

Yorkshire-fog

Favourite Grasses

The most generally palatable grass would appear to be Cocks-foot, which suits 8 species out of 10.

Small Skipper Unmown Thymelicus sylvestris Essex Skipper Unmown Thymelicus lineola Large Skipper Variable Ochlodes venata Speckled Wood Light Woodland Pararge aegeria Wall Coastal,sunny Lasiommata megera Grayling Heath Hipparchia semele Gatekeeper Hedgerows Pyronia tithonus Meadow Brown Meadows Maniola jurtina Ringlet Damp, shady Aphantopus hyperantus Small Heath Heath Coenonympha pamphilus

Butterfly Species

Table 3: BUTTERFLY PREFERENCES & HABITS

larva in hibernaculum larva or pupa small larva

1

2

1

1

1

1

2

larva in tussock larva low in clump larva low on stems larva low in clump larva, age variable

egg

1

2–3

young larva

1

Broods Winter

GRASSLAND AS A BUTTERFLY HABITAT

13

Trans. Suffolk Nat. Soc. 39 (2003)


Trans. Suffolk Nat. Soc. 39 (2003)

Grayling Small Heath Wall

Small Skipper Large Skipper

STABLE

DECLINING

Meadow

Meadow Brown

Tall coarse grasses left Unimproved grassland, uncut or lightly grazed cut annually for hay

Essex Skipper

<<SUN LOVING

Open sandy soil with patches of short grass

Rough

EXPANDING

Butterfly Population:

Habitat:

Heath

Ringlet Gatekeeper

SHADE SEEKING>> Speckled Wood

Grass in light shade around hedges or at woodland edges

Woodland

Table 4: TYPICAL HABITAT Butterfly species divided by biotope preference and status of population. All the expanding and stable species are found much more widely than the "typical" or preferred biotope. The declining species are less flexible in habitat choice, particularly in recent years.

14 Suffolk Natural History, Vol. 39


GRASSLAND AS A BUTTERFLY HABITAT

15

Butterfly Summary Table 3 is a summary of the general preferences of each butterfly, along with its characteristic habits and life-cycle features. Table 4 is a simplified allocation of butterflies to preferred habitat, which shows plainly that the species doing least well are those that live on dry sandy heaths. Diet Trials Host plant preference was investigated by means of feeding trials with 16 European butterfly species (Bink, 1985). Grasses growing in pots were placed with overlapping leaves, in such a way that larvae could move freely between 3 different grasses, from a starting point of equal numbers of larvae on each plant. 107 trials were conducted, using 30 perennial grass species. It was noted that some species (e.g. Meadow Brown, Speckled Wood and Large Skipper) were active and mobile, whilst others (Grayling and Ringlet) “hardly creep around”. Whilst the results were more meaningful for the mobile species, it was possible to grade the grasses: Rejected/Disliked/Accepted/Preferred. Only 7 of the butterfly species are found in Suffolk, and only 22 of the grasses match those already analysed in Table 2; furthermore, not every permutation was evaluated. Nonetheless, the relevant results are interesting, and have been presented as Table 5, preserving the (debatable) grassland classification used in the original. Of the 46 cases extracted from Table 2, (i.e. records exist), 17 were tried out by Bink, and 16 of these produced matches (i.e. accepted or preferred). The single mismatch was for the Meadow Brown, which rejected Upright Brome, one of the foodplants recorded by Tolman, 1997. Interestingly, Tolman was the only author to record that grass. The other 10 records of grasses rejected or disliked are not recorded in any book as foodplants for the larvae tested, and this is reassuring. The grass species found to be inedible or obviously disliked were Briza media (Common Quaking-grass), Arrhenatherum elatius (False Oat-grass) and Deschampsia flexuosa (Wavy Hair-grass). Again, it is reassuring to note that Common Quaking-grass does not feature in Table 1 because there are no records of it being used by any larvae, False Oat-grass has a single entry (Ringlet), and Wavy Hair-grass also has a single recorded consumer (Wall). Purple Moor-grass is deciduous in winter, and re-growth starts very late in the season (May); as a result, it is unsuitable for those larvae that need to start feeding early in the year. Bink draws the conclusion that preference for grass species is only a minor factor in the relationship between larva and host. Other factors such as grass quality and synchronisation of growth with the butterfly’s life-cycle are more important. He discusses the relationship between fertilizers, nutritional value and biomass production, concluding that low soil fertility favours high insect diversity, and is the best approach to reserve management. Agricultural crops are not successfully used as a host plant due to spraying and harvesting, though there are records (Dennis, 1977) for wheat (Triticum) species being consumed by Ringlet, Gatekeeper and Speckled Wood, presumably under trial conditions. Another group of grasses that are rarely eaten, are those tolerant of inundation; logical enough, given the lethality of protracted inundation to overwintering larvae.

Trans. Suffolk Nat. Soc. 39 (2003)


Trans. Suffolk Nat. Soc. 39 (2003) Species of Very Poor Grassland

Wavy Hair-grass Sheep's Fescue Purple Moor-grass Mat-grass

GRASS SPECIES OF (often acid) SOILS

Creeping Bent Red Fescue Smooth Meadow-grass

GRASS SPECIES OF ALL KINDS OF SOILS

Grayling 2

2 2

Ringlet 0

2

Small Heath 1 2

Wall 2

2

1 2

2

Meadow Brown

Species of Rather Rich Grassland

Species of Rather Poor Grassland

Table 5: HOST PLANT PREFERENCE TRIALS (After Bink, 1985) Key to Preference: 0 > Rejected Background indicates record as 1 > Disliked larval host plant (Table1) 2 > Accepted 3 > Preferred

Speckled Wood

Large Skipper 2 0

0

2

D. flexuosa F. ovina M. caerulea N. stricta

A. stolonifera F. rubra P. pratensis

16 Suffolk Natural History, Vol. 39


2

1

2

3 2 2 2 ><

3

2 0

2 2 0 3 3 2

><

2 2 3

2 2 2 2 ><

2

2 1

2 2 0 2 3

A. pratensis A. elatius C. cristatus D. glomerata E. repens F. arundinacea H. lanatus L. perenne P. pratense

A. odoratum B. pinnatum B. erecta D. cespitosa M. effusum P. bertolonii

NOTE: Bink's subdivision by soil richness is presumably based on a broad European picture but does not seem entirely valid for the situation in Suffolk. ANALYSIS by comparison with Table 2. Coincidences 17 Matches 16 Disagreement 1 [Meadow Brown reported to eat Upright Brome, but rejected it in trials]

Meadow Foxtail False Oat-grass Crested Dog's-tail Cock's-foot Common Couch Tall Fescue Yorkshire-fog Perennial Rye-grass Timothy Caterpillar with MOBILE habits:

GRASS SPECIES OF RICH SOILS

Sweet Vernal-grass Tor-grass Upright Brome Tufted Hair-grass Wood Millet Smaller Cat's-tail

GRASS SPECIES OF RATHER POOR SOILS

GRASSLAND AS A BUTTERFLY HABITAT

17

Trans. Suffolk Nat. Soc. 39 (2003)


18

Suffolk Natural History, Vol. 39

Moths The larvae of many British moths also feed on grasses, often depending on an undisturbed tussocky structure, and similar habits to those of butterfly larvae are observable. Generally feeding occurs by night, and recent evening searches in the Brecks and Sandlings have found the larvae of the Lunar Yellow Underwing moth as well as more common species. The Lunar Yellow Underwing is a nationally notable species, whose larvae feed on fine grasses of acid soils including Festuca and Deschampsia species. (Prichard, 2002). Not infrequently these searches have discovered the larvae of Grayling butterflies in the same biotope (Sherman, pers. comm., 2003). Conservation To provide foodplants for all 10 butterfly species, theoretically, one needs to plant only Cock’s-foot and Annual Meadow-grass. However, much better results will be achieved from a more diverse mix, with some attention to soil type. Graylings and Small Heaths are only likely to become established on well-drained heath-like land, and Ringlets will require some damp or shady areas, so any natural contrast between different parts of a site should be exploited. Yorkshire-fog and Cock’s-foot together will provide for the needs of all the Skippers, and most of the Browns, but an area of Sheep’s-fescue on poor, well-drained soil will also cater for the Small Heath and maximise the potential of most sites. Grass seed should be sown very thinly, perhaps at one quarter the density recommended on the packet to allow space for the wildflowers that will be required as nectar sources. Maintaining a conservation meadow is a subject of its own – see Chapter 5 of Fry & Lonsdale, 1991. Butterflies will succeed best in an open but sheltered glade, with a variety of grasses grown to maturity. In winter, clumps should remain, so a proportion of the area should be left completely uncut. If the whole area is left uncut year after year, it will unfortunately soon lose its plant diversity. In the absence of natural grazers such as rabbits, some form of selective management is therefore likely to be necessary to maintain a reasonable mosaic of sward heights. Mowing, a sudden, even and nonselective act of defoliation by scythe, sickle or machine, should not be to less than 10 cm (4 ins), and insects will fare better if the surface below is uneven. The availability of agri-environment schemes now encourages farmers to create conservation margins around agricultural land, plant hedges (with grass below), and leave some land in long-term set-aside. All this, in addition to Countryside Stewardship, does a great deal for wildlife in general, and offers butterflies of the wider countryside the prospect of more habitat across the county, with better links between areas of natural habitat. Arable field margins will provide terrain suitable for the grass feeding species to breed, especially if some of it is left uncut. It is to be hoped that such farming practice will help to check the decline of some of our common butterflies. In pursuit of such goals, the Farming and Wildlife Advisory Group (FWAG) has issued guidance on grass mixes suitable for different situations and soil types. Their “Pollen and Nectar Mix” (CSS option WM2) uses 20% Crested Dog’s-tail, 20% Meadow Fescue, 20% Sheep’s-fescue, 10% Common Bent, 10% Red Fescue, 5% Red Clover, 4% Sainfoin, 3% Common Vetch, 3% Common Knapweed and 2% Yarrow. This caters for all the Browns, but excludes the coarse grasses most

Trans. Suffolk Nat. Soc. 39 (2003)


GRASSLAND AS A BUTTERFLY HABITAT

19

favoured by the Skippers. The exclusion of coarse grasses like Cock’s-foot and False oat-grass is intentional, as their vigorous growth, and tendency to form clumps overwhelms wildflowers, reduces diversity and is generally not considered good for wildlife. Fortunately, this imbalance is redressed as the Suffolk FWAG Mixture Suggestions for 6m and 3m field margins all contain Cock’s-foot and Timothy, so the Skippers are thus provided for elsewhere on the farm. In a practical conservation situation, it is desirable that coarse grasses are allowed to flourish in the 3 metres closest to the hedgeline, where the clumps will benefit small mammals as well as caterpillars, and this outer border can be cut just once in 3 years, to inhibit the spread of hawthorn and bramble from the hedge. The inner 3 metre field margin may be cut more frequently, say once in spring and once in August to protect the crops from invasion by weeds like cleavers. The Pollen & Nectar mix is used for conservation corners, and an “innoculation” is also recommended in the field margin sowing, to spread some pollen and nectar more widely around the farm. This practice will benefit butterflies as well as bees and beetles. Conclusion The foregoing analysis has done no more than match our 10 grass feeding butterflies to a range of foodplants, and comment on their present status. Perhaps the most significant observation is that the dramatic loss of grassland diversity of the past 50 years has had a direct impact on the fortunes of many of our once common butterflies; it may be too late to check the decline of all but the most adaptable species. This review did not reveal any real surprises, but should provide a helpful foundation for watching the progress of those species that are extending their range, as well as those in decline. There is scope for field observations to verify that the theoretically suitable grasses are in fact in use in Suffolk. It is to be hoped that this article will generate some co-operation between those who know their grasses and those prepared to make field observations to discover which grasses are chosen for egg-laying. Being able to offer specific advice on which grasses to sow in a conservation mix for butterflies is useful spin-off, at a time when farmers are actively increasing margins suitable for butterflies. Verification Future observations to confirm or refine the above tables would be very welcome. Neil Sherman has made some good observations recently, and others are urged to look for the right opportunities, perhaps at sites they know well. The best information would be: a. Field observations of butterflies laying eggs on positively identified grass species. b. Field observations of positively identified caterpillars feeding on particular grasses in the wild. c. Breeding trials to confirm acceptability of known grass species, and resulting in successful completion of the whole life-cycle.

Trans. Suffolk Nat. Soc. 39 (2003)


20

Suffolk Natural History, Vol. 39

Samples of the grass in question should be taken, ideally from the very same plant in use – if it is possible to do this without removing the egg/caterpillar – and should include the whole plant from root/stolon up to inflorescence, if in flower. Samples should be kept dry, at all costs avoiding moulding in a polythene bag; if dry they will remain identifiable forever. Such observations should also record site details, and the apparent strength of the colony in the wild. Acknowledgements Thanks are due to Arthur Copping for his detailed comments on botanical aspects of the text, and to Kevin Walker of CEH and Ron Porley of English Nature for guidance of a broader nature. I am grateful too, for assistance from Nick Gibbons, Eddie John and to Roger Dennis, who drew my attention to Bink’s earlier work on this topic. References [Code used in Table 1] Asher, J. et al., (2001). The Millennium Atlas of Butterflies in Britain & Ireland. Oxford: Oxford University Press. [2] Beaufoy, S. (1947). Butterfly Lives. London: Collins. [7] Bink, F. A. (1985). Host plant preference of some grass feeding butterflies. Proc. 3rd Congr. eur. Lepid., Cambridge 1982. pp. 23–29. Carter, D. J. & Hargreaves, B. (1986). A Field Guide to Caterpillars of Britain & Europe. London: Collins. [1] Copping, A. (2003). Grasses on Wortham Ling 2001, unpublished list. Dennis, R. L. H. (1977). The British Butterflies – Their Origin and Establishment. Classey. Fry, R. & Lonsdale, D. (Eds) (1991). Habitat Conservation for Insects – A Neglected Green Issue. AES. Middlesex: Amateur Entomologists’ Society. Hawley, P. (1989). Grasses. Shire Natural History. Hill, J. K., Thomas, J. A., & Huntley, B. (1999). Climate and habitat availability determine 20th century changes in a butterfly’s range margin. Proceedings of the Royal Society of London B, 266: 197–206. Hubbard, C. E., 1984. Grasses. Penguin Mendel, H. & Piotrowski S. (1986). The Butterflies of Suffolk. Ipswich: Suffolk Naturalists’ Society. [6] Porter, J., (1997). Caterpillars of the British Isles. Viking. [4] Prichard, A. W. (2002). Moth Night at King’s Forest. White Admiral 54. Rodwell, J. S. et al, (1992). British Plant Communities. Cambridge: Cambridge University Press. Thomas, J. & Lewington, R. (1991). The Butterflies of Britain & Ireland. London: Dorling Kindersley. [5] Tolman, T. & Lewington, R. (1997). Butterflies of Britain & Europe. London: Collins. [3] Schowalter, T. D. (2000). Insect Ecology. San Diego: Academic Press. Shreeve, T. G., (1986). Egg-laying by the Speckled Wood butterfly. Ecological Entomology 11: 229–236. Simpson, F. W. (1982). Simpson’s Flora of Suffolk. Ipswich: Suffolk Naturalists’ Society.

Trans. Suffolk Nat. Soc. 39 (2003)


GRASSLAND AS A BUTTERFLY HABITAT

21

Stace, C. (1997). New Flora of the British Isles, 2nd Edition. Cambridge: Cambridge University Press. Stewart, R. (2001). The Millennium Atlas of Suffolk Butterflies. Ipswich: Suffolk Naturalistsâ&#x20AC;&#x2122; Society. Rob Parker 66, Cornfield Rd, Bury St Edmunds, Suffolk, IP33 3BN

Trans. Suffolk Nat. Soc. 39 (2003)

SUFFOLK GRASSLAND AS A BUTTERFLY HABITAT  

Rob Parker

Read more
Read more
Similar to
Popular now
Just for you