1631       Poecilocampa populi (Linnaeus, 1758)     DECEMBER

A widespread species in the British Isles, the larva feeding on a large range of deciduous trees and shrubs.  In Dorset, the moth is abundant in deciduous woodland containing birch (Betula spp.), elm (Ulmus spp.), hawthorn (Crataegus spp.) or blackthorn (Prunus spinosa), and common amongst coastal blackthorn thickets, but less frequent elsewhere.  The moth is readily attracted to light and has been observed by the author, flying at a lighted window in sub-zero temperatures and snow falling.

1632       Trichiura crataegi (Linnaeus, 1758)    PALE EGGAR

A species occurring in England and Wales becoming less frequent as one heads north, the larva feeding on hawthorn (Crataegus spp.), blackthorn (Prunus spinosa), birch (Betula spp.), sallow (Salix spp.) and heather (Erica spp.).  In Dorset, the moth occurs at low density in open or wooded districts where blackthorn or hawthorn is frequent.  It is rarely observed on sandy soils.  The Pale Eggar appears to have become scarcer in recent years, in parallel with the decimation of blackthorn and hawthorn scrub on downland.

1633       Eriogaster lanestris (Linnaeus, 1758)    SMALL EGGAR     Notable/Nb

A local species in England, the larva feeding on blackthorn (Prunus spinosa), hawthorn (Crataegus spp.) and dog-rose (Rosa canina).  In Dorset, the moth has a similar distribution to the Pale Eggar, but is primarily associated with blackthorn.  When young, the gregarious larvae are relatively easy to find due to the large and highly visible webs they create on host bushes. Several hundred caterpillars may inhabit a single web and significant defoliation may result in the immediate vicinity of the web but not enough to endanger the host plant.  When almost full-grown, the larvae disperse, occasionally over relatively long distances. The hairs from the caterpillar can cause irritation to skin.  The moth may not emerge from its pupa for three years or more, but overwintering once in this stage tends to be the norm.  Although the species is present in the county, it is markedly scarcer than it used to be, and this is probably directly due to man-related activities.  Like the endangered Brown Hairstreak butterfly, the Small Eggar seems to prefer untended blackthorn bushes and hedgerows.  Land management policy of precision-strimming hundreds of miles of the county’s hedgerows, whether they line footpaths, bridleways, minor roads or major roads, has undoubtedly reduced favourable habitat for both species. On top of hedgerow degradation come wind-borne chemical drift from agricultural pesticide sprays targeted at crops that inevitably envelop and contaminate boundary hedgerows.  Lydlinch Common in the Blackmore Vale is a stronghold for both the Brown Hairstreak and the Small Eggar, and comprises small compartments of ancient common land with large quantities of unkempt blackthorn.  Conservation measures on this SSSI should include the maintenance on rotation of sloe scrub in various stages of growth. In some years the Small Eggar is also common on coastal blackthorn scrub between Weymouth and Cogden.

1634       Malacosoma neustria (Linnaeus, 1758)    LACKEY

A species found in England and Wales becoming less frequent as one heads north, the larva feeding on a variety of deciduous shrubs and plants. The larvae, which are highly distasteful to birds, behave in the same gregarious way as the Small Eggar₁₆₃₃, spinning a web on the host shrub to house the colony.  The blue markings on the caterpillar are not pigment but Tyndall Blue, a colour derived from the interaction of light and micro-structures on the insect.  When almost full-grown, the larvae disperse. In Dorset, the moth is abundant in coastal districts, especially where blackthorn (Prunus spinosa) thickets abound. Inland, the moth ranges from common on chalky soils to rare on sandy soils.

1636       Lasiocampa trifolii  [Denis  & Schiffermüller 1775]    GRASS EGGAR      Notable/Na

A local and declining species found in less than ten counties in England and Wales, inhabiting sandhills, sea-cliffs and inland heaths, the larva feeding on a wide range of shrubs and plants.  In Dorset, the moth, which is on the wing in August, has declined considerably and is now at very low ebb, with just a handful of colonies remaining.  This retrogressive pattern appears to be synchronised with the fragmentation of large heathland blocks and loss of continuous unimproved coastal grassland tracts.  Most of the colonies are located within SSSIs but given the dramatic decline in populations nationally, the Grass Eggar is undoubtedly a candidate for a species recovery program.  A primary recommendation is the continued monitoring of this species to establish year on year trends.

Coastal Dune and Heath

A few colonies persist among coastal dunes and heaths at Studland.  However, old records indicate that the moth was also present in the Canford Cliffs area of Poole and further east in the region of Hengistbury Head.

Rocky Coast

Recent light trap records from sea cliff habitat between Portland and Durlston suggest that the Grass Eggar may still be resident in unimproved coastal grassland along the Purbeck coast.  A recent record from Portland may refer to wanderers from such colonies as the absence of records from regular trapping on Portland suggests that the moth does not occur on the island at the present time.  Records of note from rocky coast habitat include: Holworth and Arish Mell, not uncommon on the rough undercliff (FHF), Durdle Door, three larvae on 1 May 1953 (FMBC, HS), White Nothe, larva on 28 May 2003 (MF, PH), Swanage, larva on 29 March 1927 (JRB).

Inland Heath

A few colonies have been found recently on inland heaths.  However, old records make it clear that the species was far more widespread than today with colonies present over a wide area of the Poole basin.  The moth has disappeared from all the heathland blocks outside Purbeck, and the retrogressive pattern experienced in Hampshire appears to have been mirrored in Dorset.

1637       Lasiocampa quercus  (Linnaeus, 1758)    OAK EGGAR

A species occurring widely across Britain, the larva feeding on a wide range of shrubs and plants.  In Dorset, the species is most often seen in open unimproved habitats, and it is particularly common in coastal districts.  The male is active during the day when it may be seen flying vigorously, if a little haphazardly, inpursuit of the female pheromone.  Assembling with a virgin female may lead to the rapid appearance of several male suitors.

1638       Macrothylacia rubi (Linnaeus, 1758)    FOX

A widespread and locally common species in Britain, the larva feeding on a wide range of shrubs and plants.  In Dorset, the species is most often seen in open habitats.  It is particularly common on heathland and in open grassy tracts in deciduous woodland (eg. Stubhampton Bottom) and scrub (eg. Lyscombe Hill) on chalky soils.  The adult male Fox behaves in a similar way to the adult male Oak Eggar₁₆₃₇, flying strongly over open country during the day.

1640       Euthrix potatoria (Linnaeus, 1758)    DRINKER

A common species over England and Wales, less frequent further north, the larva feeding on broad-bladed grass species such as common reed (Phragmites australis), cock’s-foot (Dactylis glomerata) and reed canary grass (Phalaris arundinacea).  The nocturnal- feeding caterpillar can be found characteristically in-situ on the stem of its foodplant during the day.  In Dorset, the moth is widespread and common, but rises to abundant in reedbeds, inland marshes, river and stream valleys, and the moister woods.  It is locally abundant on coastal grassland on chalky soil, notably on Portland, St Alban’s Head and Durlston, and in this drier biotype the foodplant is likely to be tor-grass (Brachypodium pinnatum).

1642       Gastropacha quercifolia (Linnaeus, 1758)    LAPPET

A species found in southern Britain, the larva feeding on blackthorn (Prunus spinosa), hawthorn (Crataegus spp.), buckthorn (Rhamnus cathartica), sallow (Salix spp.), wild plum (Prunus domestica), and apple (Malus spp.).  This is the largest of the ‘Eggars’, the caterpillar measure up to 90mm long when fully grown.   In Dorset, the moth is thinly scattered and at low density, but not uncommon where hawthorn and blackthorn predominate. The Lappet, like the Pale Eggar₁₆₃₂ and the Small Eggar₁₆₃₃, appears to have become less frequent in recent years, and changes in the management plus the removal of scrub and hedgerow habitat on chalky soils undoubtedly accounts for the decline of all three species. Chamberlaynes: “A female emerged from pupa, taken as a larva at Tincelton, in late afternoon of 13 July 1935 and was left in a cage in my bedroom.  The unfortunate male had been attracted in and was found fluttering in a slop-pail the next morning.  The male was put outside, however, the same male reappeared inside after dark, but this time was found in a jug of milk” (H Andrewes).