Species Statement
Essex Emerald (Thetidia smaragdaria maritima)
©Roger Key, English Nature
Image enquiries: Roger Key
Current status
The Essex emerald moth occurred on coastal saltmarshes. In Britain sea wormwood Artemisia maritima was the only recorded larval foodplant. The site of the last known colony, in Kent, was a south-east facing earthen sea wall at the foot of which sea wormwood grew in clumps with much adjacent bare, sun-baked soil. There was a thriving rabbit population on site which created much of the bare soil. The foot of the sea wall was occasionally inundated by sea water but larvae were found much further from the strandline at other former sites, where inundation is not an annual event. At the last Essex colony most larvae were found on broken ground only recently colonised by sea wormwood growing in an almost pure stand, though a few larvae were found on plants growing amongst grasses. The eggs were laid singly on the younger upper shoots of sea wormwood and the young larvae usually fed on this new growth. The larvae took up lower positions on the plant for hibernation, feeding on new shoots in the spring but spinning loose cocoons lower down again on the older stems. The adults could be found by day among the larval foodplant. Larval counts on former sites were often several hundred but since the 1970s the last two populations never had larval counts exceeding a hundred.
The British population was recognised as a distinct sub-species, Thetidia smaragdaria maritima, in 1935. T.s.maritima has been recorded only from the coastlines of Essex and Kent, where it is now believed extinct. It was formerly recorded from at least 10 ten km squares. The last populations died out in 1985 and 1990/91 in Essex and Kent respectively. The Essex emerald occurs in Japan, Amur and northern China through Siberia and central Asia to western Europe and from southern Scandinavia to the Mediterranean.
In Great Britain the Essex emerald is classified as Extinct.
Current factors causing loss or decline
Factors which are implicated in the extinction of the Essex emerald, and which may act as constraints to recovery, include:
Inappropriate grazing management.
Inappropriate management such as cutting the vegetation on sea walls and too frequent fires.
Large-scale reconstruction and subsequent maintenance of sea walls.
Loss and fragmentation of habitat due to agricultural improvement of upper saltmarsh and industrial development of the Thames estuary.
Loss of genetic variability due to the small size of the remaining populations may have been a factor.
Although collecting is not considered the main cause of extinction, small populations were almost certainly vulnerable.
Current action
Major surveys of Essex and Kent in 1987 and 1988 found larvae in only one saltmarsh system, in Kent. This site was monitored annually up to 1993.
Captive stock survived to 1996 as the result of a captive breeding programme initiated in 1987.
Between 1990 and 1993 five attempts, at three sites, were made to try and establish wild colonies from captive stock, initially by the Nature Conservancy Council and then as part of the Species Recovery Programme, without long-term success.
www.ukbap.org.uk/UKPlans.aspx?ID=602
