#73 Small Eggar by Sam Newton
Meet Sam Newton, naturalist, ecologist, and biological recorder!
Sam Newton is Woodland Creation Officer at the North York Moors National Park where he has been responsible for delivering the Authorities Woodland Creation Grant Scheme since 2020, and prior to that was Natural Heritage Officer on the National Parks Land of Iron Project, which focussed on helping nurture the wildlife in areas of previous ironstone mining. He also carries out bat emergence surveys for the Thirsk based ecological consultancy MAB Ecology.
Outside of work, he is a Yorkshire Butterfly Conservation practical volunteer leader and committee member, walks a Butterfly Transect near Hawnby, and monitors a Pearl Bordered Fritillary site. He also volunteers for the North York Moors National Park, leading volunteer tasks with the MADs (Make a Difference) Group, and carrying out water vole, grassland, and turtle dove surveys. Away from (and often whilst) volunteering he is an all-round biological recorder (and iRecord obsessive) and attempting PAN species lister (when he finds time to catch up on records and pull his list together). He is also Mammal Recorder with the Ryedale Natural History Society, Coleoptera Recorder with the Scarborough Field Naturalists, and member of the North-East Yorkshire Botany Group. Saturday afternoons, however, are reserved for cricket!
Sam can be contacted via email at sam.newton@yorkshirebutterflies.org.uk.
Small Eggar caterpillars on their larval web
The moth Small Eggar Eriogaster lanestris is Sam’s chosen species. He first came across their distinctive larval webs in 2019 when carrying out a turtle dove survey near Hovingham. This chance encounter has led to a yearly obsession of finding their distinctive larval webs. You can find out more about this species on the Yorkshire Moths website.
The Small Eggar is interesting in that adults are rarely recorded, possibly as few people moth trap from late February to early April when the adults fly. However, soon after hatching from late April to early July, caterpillars build and live gregariously on compact larval webs on south facing blackthorn and hawthorn scrub and hedgerows. These webs absorb thermal energy, and the caterpillars use this to control their temperature (‘tent-based thermoregulation’), allowing them to metabolise faster and pupate sooner. Caterpillars also carry out highly synchronised foraging bouts from the web onto the surrounding foodplant (‘central placed foraging’), using chemical trails to mark their routes (‘trail-based communication’).
The Small Eggar has a long history in Yorkshire. In 1883 Porritt listed several known sites across the county, but mostly in the centre and east. At that time there were also records further north in Northumberland and Durham. However, by 1907 Porritt listed just three localities, and the last record further north was in 1899. By 1989 Sutton and Beaumont outlined that ‘This species has declined seriously over the whole country… Yorkshire now being one of its last strongholds. It can be found at various sites in the Pickering area’. This Pickering population is clearly shown in the 2019 Atlas of Britain & Ireland's Larger Moths, as part of a severly fragmented national distribution.
Male Small Eggar
Vast destruction of hedgerows coupled with modern intensive management, and pollution from vehicles and agricultural drift have often been quoted as key drivers of decline. To try and understand this, Sam studied the Small Eggar for his MSc dissertation from 2019-2020, surveying to try and understand distribution, and looking at variables relating to scrub/hedgerow structure and composition in order to get an insight into their habitat requirements.
Typical view of a Small Eggar larval web on a hedgerow
Results showed a population more widespread than previously thought, centred on the western Vale of Pickering, but reaching south past the Howardian Hills and into north-western East Yorkshire. Habitat requirement indicated selection of exposed locations with fewer nearby trees, on hedgerows that were longer and better connected, and comprised of mainly blackthorn and hawthorn (two thirds were on blackthorn) – all linking to enhanced ‘tent-based thermoregulation’ and increased potential for web attachments, available food, and ventilation and sunlight. The results also appeared to show that managed (i.e. flailed) hedgerows were preferred, however, many webs have been found on successional scrub and unmanaged hedgerows, which suggests they are using the habitat that is now available to them (i.e. most hedgerows are now flailed) and that areas of scrub and hedgerows cut less often would be used more often if more widely available.
Small Eggar have likely benefited from modern hedgerows regulations and the creation of new hedgerows, in comparison to the past when there was widespread loss of hedgerows, and indiscriminate cutting when egg masses and larval webs may have been active.
Recording and monitoring
This is not the full story. It is puzzling that so few larval webs are seen unless they are being actively searched for. Have modern naturalists sacrificed recording along lanes and footpaths for the ease of getting into their cars to visit ‘interesting sites’ (e.g. several records come from the popular Ellerburn Banks YWT Reserve)? Why else are these larval webs not seen? Are there further colonies in Yorkshire, and how far does the Vale of Pickering colony really extend? Sam will keep searching.
Distribution of Small Eggar in Yorkshire. Black 5km dots = Modern records up until 2023; Grey = Historical records.
Further information and acknowledgements
I would like to thank Dr David Wainwright (Head of Conservation at Butterfly Conservation), Dr Charles Fletcher (Yorkshire County Moth Recorder), and Dr Robert Woods (VC62 Moth Recording Co-ordinator) for their advice and maps during my time studying Small Eggar, and Jon Hogg (Butterfly Conservation volunteer) and Gill Smith (Ryedale Natural History Society) for directing me to Small Eggar larval webs they have found. NEYEDC would like to thank Sam for his time and expertise in helping to create this blog.
References:
Randle, Z., Evans-Hill, L.J., Parsons, M.S., Tyner, A., Bourn, N.A.D., Davis, A.M., Dennis, E.B., O’Donnell, M., Prescott, T., Tordoff, G.M. and Fox, R. (2019) Atlas of Britain and Ireland’s Larger Moths. Newbury: Pisces Publications.
Ruf, C. and Fiedler, K. (2002a) ‘Tent-based thermoregulation in social caterpillars of Eriogaster Lanestris (Lep. Lasiocampidae): Behavioural mechanisms and physical features of the tent.’ Journal of Thermal Biology, 27(6), pp. 493-501.
Yorkshire Moths Website (2024) Yorkshire Moths: Small Eggar. [Online] Available at: https://yorkshiremoths.co.uk/index.php?bf=16330&v=t (Accessed 21 October 2024)