Observations of the Holly Blue butterfly

OBSERVATIONS OF THE HOLLY BLUE BUTTERFLY E . PARSONS

From a low ebb in 1988 the Holly Blue, Celastrina argiolis population in Suffolk exploded in 1990. The species was seen in numbers again in 1991.

Population explosions of this kind are a characteristic of the Holly Blue that have been of interest to naturalists for many years.

The accepted account of the life-history of the Holly Blue is one of the alltime entomological favourites and, if only for this reason, naturalists should consider it worthy of some interrogation. Furthermore, much of our current understanding of butterfly ecology is based upon the observations of early naturalists who were often collectors essentially. Their records may have been secondary to a primary objective of cultivating specimens and wildlife in captivity may deviate from its normal, natural pattern of behaviour.

Little fundamental change has taken place in the understanding of the Holly Blue since it was recorded in a paper by R. Adkin in 1896 and later noted by Richard South (Howarth, 1973). Briefly, Holly Blue butterflies emerge in Spring from pupae that have overwintered attached by slender threads to the leaves of Ivy, Hedera helix L. and, soon after, they search for Holly, Ilex aquifolium L. The mated female places Single eggs on, or close to, the developing berries of the Holly and after a week larvae hatch and feed on nearby berries where they remain for the greater part of the larval stage, changing their position only during moults. After four to six weeks they pupate beneath a nearby leaf. The second brood of butteflies appears in late July and they in turn search for the flowers and developing berries of Ivy where a similar series of events takes place, excepting that the resulting pupae overwinter.

Many alternative foodplants have been identified for Holly Blue larvae: Dogwood, Cornus sanguinea L., Berry-bearing Alder, Frangula alnus Mill., Spindle, Euonymus europaeus L., Furze, Ulex europaeus L., Bramble, Rubus sp., and Firethorn, Pyracantha atalantioides L. On the 24th August 1989, a final instar Holly Blue larva was beaten from, and subsequently reared on Sallow, Salix cinerea L., by Dr. P. Henwood in Devon. M. D. Crew (pers. comm.) reported Holly Blue butterflies laying eggs in May 1991 on the foliage of immature Spindle, Euonymus fortunei, Dyers Greenweed, Genista tinctoria L. and Cotoneaster, Cotoneaster horizontalis Decaisne, in a nursery. Other plants where oviposition has been reported in Britain include: Rhododendron, Rhododendron sp., Crown Vetch, Coronilla varia L., Wayfaring Tree, Viburnum lantana L., Spindle, Euonymus japonicus, Wisteria, Wisteria sinensis, and Lucerne, Medicago sativa, L. On the Continent the appetite of the species extends also to Heathers, Calluna sp. and Erica sp., Billberry, Vaccinium sp., Pear, Pyrus sp. and others. One author described the various foodplants of a population of Holly Blue in Ostergotland, Sweden, where no Holly or Ivy occurs (Gardiner, 1992). From this diverse list I can only confirm Dogwood, Cornus sanguinea L. (ssp. sanguinea), and P. atalantioides as alternative foodplants of Holly Blue larvae in

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18 Suffolk Natural History, Vol. 28 Suffolk from eggs laid in spring, but such is the polyphagous nature of the species that no others can be dismissed.

When exploring the possibility of an alternative foodplant it needs to be ascertained whether or not hatched larvae can be sustained by the plant on which the egg was laid. Eggs may be freely placed on unsuitable plants by th species (Russell, 1991). Personal experience demonstrated the failure of larvae on some Holly foliage. Ornamental hollies usually produce berries when they are still quite young and in my experience are widely used by Holl Blue, especialy in the urban environment. Holly trees are either male or female and only the femaleflowersform berries. It was possible to compare two small ornamental Hollies, I. aquifolium, 'Golden King' and 'Silver Queen', one female and the other male, respectively. Neither was more than Im high and both shared the same border 5m apart. Eggs of Holly Blue wer found on theflowersof both bushes in late April. Although larvae were present and feeding on the berries of the female Holly, apart from a sma amount of damage to some leading shoots for which Holly Blue larvae may have been responsible, none could be found on the male bush where the spentflowershad by then been dropped.

Eggs were nearly always placed singly on the underside of developing berries, or on the stalks supportingflowersor berries. Butterflies would typically pirouette on a chosenfloweror berry with their wings held together over their backs for several seconds before they produced an egg. These were carefully placed by the butterfly which curled its abdomen to reach a suitable site to attach an egg. The eggs adhered to the plant with an adhesive produced by the butterfly. Invariably a shortflightfollowed the production of an egg and minutes elapsed before the female would again begin investigating another site. I planted a hedge from wild, rooted layers of mixed male and female holly in 1976 and one unchecked plant is today about 3 metres high the remainder having been trimmed to about 2 metres. 1990 was thefirstyear that the hedge produced any significant amount offlowers.The crop of flowers was prodigious. They were found by Holly Blue butterflies by la April which then fed upon theflowersand laid eggs. I observed the developing larvae daily. At the other end of our garden a Firethorn hedge was also supporting Holly Blue, but to a much lesser extent. I was able to fi only 4 or 5 larvae at any one time over a greater volume of hedge, whereas on the smaller mass of the Holly it was easy tofinda score or more at mo times throughout May and early June. The Firethorn was established at the same time as the Holly from rooted cuttings and, although it has produced berries annually, I had never previously noticed Holly Blues showing an interest in it. I suggest that the Firethorn was being used as an alternative to 'oversubscribed' Holly. However, the mature larvae feeding on Firethorn in June became very obvious as the berries began to ripen and change colour- a Problem not faced by larvae on the nearby Holly at the same time Larvae were usually difficult to spot, remaining well camouflaged and apparently

Butterflies oviposited in our garden from the 4th week in April up to the second week in June, and over much of the period it was possible to fin larvae in vanous stages of development. A small number were raised in Trans. Suffolk Nat. Soc. 28 (1992)

19 captivity from eggs and it was possible to identify larvae ready for pupation by a change in their body colour to a duller shade of green. Although captive larvae pupated beneath a leaf within the confines of their Containers, the wild larvae when ready to pupate disappeared and I often could notfindthem or pupae, in spite of thorough searches. The very few pupae that I didfindwere at ground level under Hollies and only one of those was positively attached to anything. I found it attached by a few threads to the underside of a small clod of earth beneath a small ornamental Holly, I. meservae, 'Blue Princess'.

The particular success of Holly Blues in 1989 and 1990 may be attributed to a pattern of dry 'Indian' summers and generally frost-free winters in 1988, 1989 and 1990. Fruiting of both Holly and Ivy was enhanced in 1989 and 1990.

It is difficult to be certain whether Ivy has particularly benefited in recent years, but there is strong circumstantial evidence to suggest that it has. The presence of quantities of dead and ailing Elms has provided Ivy with many open sites in the countryside and the transpiration difficulties experienced by many trees in hot, dry summers could result in canopy reduction to the advantage of the ripening wood of associated Ivies. An absence of hard frosts in subsequent winters might have preserved exposed pupae and further enhanced the spring emergence. Populations of Holly Blue butterflies subject to predation by parasites follow a recognised pattern of cycles as numbers of parasites increase to proportionally overtake those of their hosts and then 'crash' themselves. I believe that four elements converged to favour the Holly Blue in the period 1989-1990: extended summers, an abundance of food, frost-free winters and a low level of parasitism.

I thank S. H. Piotrowski and H. Mendel for their guidance and help in the preparation of this manuscript and those who granted me access to their properties and allowed me to pull their plants about.

OBSERVATIONS OF THE HOLLY BLUE BUTTERFLY

References Adkin, R. (1896). Proc. S. Lond. ent. Nat. Hist. Soc. Blowers, K. etal. (21.2.90,24.2.90,20.3.90,17.4.90,15.6.90,4.8.90,12.1.90 etc.) Weather reports. East Anglian Daily Times: Ipswich.

Ford, E. B. (1977). Butterflies London: Collins (New Naturalist Series).

Gardiner, B. O. C. (1992). Foodplants of the Holly Blue butterfly Celastrina argiolish. (Lep.: Lycaenidae)-some continental records. Ent. Ree., 104, 70.

Goldsmith, E. T. (1953). The Holly Blue, Trans. Suffolk Nat. Soc. 8, 81.

Heath, J., Pollard, E. & Thomas, J. (1984). Atlas of Butterflies in Britain and Ireland. Middlesex: Viking.

Henwood, P. (1991). Larva of Celastrina argiolis L., Holly Blue (Lep.: Lycaenidae) feeding on Sallow. Ent. Ree., 103, 134.

Holman, R. M. & Robbins, W. W. (1933), Elements ofBotany. London & New York: John Wiley & Sons, Inc. Howarth, T. G. (1973). South's British Butterflies. London: Frederick Warne.

Newman, H. L. (1977). Looking at Butterflies. London: Collins.

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Imms, A . D . (1973). Insect Natural History. London: Collins. (New Naturalist Series).

Mendel, H . & Piotrowski S. H . (1986). The Butterflies of Suffolk. Ipswich Suffolk Naturalists' Society.

Pollard, E . & Hall, M. L. (1989). Buttefly Monitoring in 1988. Entomologist, 108, 229.

Russell, P. J. C. (1991) A Holly Blue Ovipositing on Corilla varia. A E S Bulletin. 50, 105.

E . Parsons 41 Dover R o a d , Ipswich, Suffolk, IP3 8 J Q

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Nat. Soc. 28 (1992)

Plate 1: Larva of Holly Blue (Celastrina argiolus) which has been very common in recent years. (p. 17).