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A review of the pollinators associated with decaying wood, old trees and tree wounds in Great Britain
Abstract
A provisional listing of over 320 species of British flower-visiting insects (mostly Coleoptera, Diptera and aculeate Hymenoptera) that are fully or substantially reliant on old trees, dead wood, tree wounds and other timber for larval development. The report summarises the ecology (including larval biology and floral preferences), distribution, status and broad conservation requirements for most species. The report also explains in more general terms the conservation requirements for this assemblage as a whole and is liberally furnished with photographs of the insects and their key habitats.
... Lewis 1998;Jonsell et al. 2004). Maintaining or even creating "open" space such as forest edges, glades or places around legacy trees is also needed to increase the species richness of adult feeding sources like flowering herbs, shrubs and trees as in Syrphidae adult flower visiting occurs close to the larval tree-related habitats, typically on the forest margin itself and up to 100-200 m into open meadows (Ssymank 1991(Ssymank , 2001Falk 2021). About 10-15% of trees should be decaying snags or stumps and logs. ...
... 1. Review the knowledge on faunistics of the target species or genera (Rotheray, 2013;Pérez-Bañón et al. 2016; van Steenis et al. 2020;Falk 2021). 2. Search for additional populations of the species through targeted search for suitable habitat, host trees or accompanying species such as the European velvety tree ant (Liometopum microcephalum (Panzer, 1798)) in the case of Sphiximorpha petronillae (Birtele 2003;Del Toro et al. 2009;Sebel et al. 2013;Mei 2016;Miklín et al. 2017;Griffiths et al. 2018;Tăuşan 2018; van Steenis et al. 2019;Bütler et al. 2020;Petermann & Gossner 2022 (Quinto et al. 2012;Sánchez-Galván et al. 2014;Krivosheina 2019Krivosheina , 2020. ...
... 8. Creating breeding boxes to be used during population dynamic studies or in young growth forests to establish jumping populations to and from isolated wild populations (Maibach & Goeldlin 1992;Rotheray 2004;Carlsson et al. 2006;Schmid & Moertelmaier 2007;Jansson et al. 2009;van Steenis 2015;Landvik et al. 2016). 9. Investigate how to incorporate nature conservation actions with raising awareness to the people through social media and citizen science (Read 2000;Flint et al. 2009;Thorn et al. 2020;Falk 2021). ...
The bee-mimicking hoverfly species Criorhina pachymera shows pronounced geographical variation in abdominal colour pattern. Based on 218 records from 22 European countries, we describe six abdomen forms divided over two main groups. Group A in western, northern and central parts of Europe contains abdomen forms A1–A3 with slender pollinose bands on the third and fourth tergite. Group B in south-eastern Europe contains forms B1–B3 with broad pollinose bands. These groups are separated by the Alps and the Carpathians, such as the separation of the original distributions of the two main postglacial recolonization lineages of honey bees in Europe. As these honey bee groups differ by the width of the pollinose bands on the third to fifth tergite, Batesian mimicry can explain the group distribution of C. pachymera with slender or broad pollinose bands. The different forms of C. pachymera in both groups are categorised by the extent of orange colouration on the second and third tergite. The darkest form A1, has a widespread distribution in Europe. Intermediate bright forms A2 and A3 occur predominantly in a belt along the southern margin of the group A distribution and in Sweden. Dark form B1 and intermediate bright form B2 occur on the Balkan peninsula and in neighbouring regions. The brightest form B3, is found in Italy, Switzerland (Ticino) and Greece. There is an average increase in the extent of orange colouration on the second and third tergite with decreasing geographical latitude, making temperature a likely additional cause for the described abdominal colour variation.
... Lewis 1998;Jonsell et al. 2004). Maintaining or even creating "open" space such as forest edges, glades or places around legacy trees is also needed to increase the species richness of adult feeding sources like flowering herbs, shrubs and trees as in Syrphidae adult flower visiting occurs close to the larval tree-related habitats, typically on the forest margin itself and up to 100-200 m into open meadows (Ssymank 1991(Ssymank , 2001Falk 2021). About 10-15% of trees should be decaying snags or stumps and logs. ...
... 1. Review the knowledge on faunistics of the target species or genera (Rotheray, 2013;Pérez-Bañón et al. 2016; van Steenis et al. 2020;Falk 2021). 2. Search for additional populations of the species through targeted search for suitable habitat, host trees or accompanying species such as the European velvety tree ant (Liometopum microcephalum (Panzer, 1798)) in the case of Sphiximorpha petronillae (Birtele 2003;Del Toro et al. 2009;Sebel et al. 2013;Mei 2016;Miklín et al. 2017;Griffiths et al. 2018;Tăuşan 2018; van Steenis et al. 2019;Bütler et al. 2020;Petermann & Gossner 2022 (Quinto et al. 2012;Sánchez-Galván et al. 2014;Krivosheina 2019Krivosheina , 2020. ...
... 8. Creating breeding boxes to be used during population dynamic studies or in young growth forests to establish jumping populations to and from isolated wild populations (Maibach & Goeldlin 1992;Rotheray 2004;Carlsson et al. 2006;Schmid & Moertelmaier 2007;Jansson et al. 2009;van Steenis 2015;Landvik et al. 2016). 9. Investigate how to incorporate nature conservation actions with raising awareness to the people through social media and citizen science (Read 2000;Flint et al. 2009;Thorn et al. 2020;Falk 2021). ...
This paper introduces the importance of veteran trees, tree related microhabitats (TreMs) and their associated hoverfly (Diptera, Syrphidae) fauna. A broader perspective of creating larval habitat is discussed, based on published and novel insights. It focuses on hoverflies that specialise on veteran trees and reflects upon protection and management regimes to conserve veteran trees, TreMs and associated woody habitats. The lack of veteran trees breeding sites can be resolved by tree veteranisation or by using artificial breeding boxes. Whilst protection of veteran trees is essential, enhancement of open areas with flower resources is also vitally important for the survival of saproxylic hoverflies. The larval and adult ecology of only three out of the 134 known European saproxylic species are properly understood. Thus several suggestions are offered for future research aimed at a thorough understanding of the natural history of this unknown and ecologically relevant group of species. The list includes faunistic surveys and investigations into population dynamics, dispersal capacity and habitat preferences. Alongside this research there is a need to investigate the creation of breeding sites including veteranisation techniques and the use of breeding boxes.
... Despite growing recognition that forests provide important habitats for saproxylic bees and wasps (Bogusch and Horák 2018;Falk 2021) and that the group is sensitive to management decisions (Westrich 1996;Westerfelt et al. 2015;Hanula et al. 2016;Lettow et al. 2018), few specific guidelines have been developed for supporting their diversity in forests Bogusch and Horák 2018). At the same time, saproxylic bees and wasps differ from saproxylic beetles in their biology and ecology. ...
... Also, large solitary trees, i.e. veteran trees, are known to support high saproxylic biodiversity as well as a high number of hymenopteran species (Sebek et al. 2016). In the case of saproxylic organisms, it is likely due to the availability of sunlit deadwood as well as the diversity of available microhabitats, crucial resources for most saproxylic insects (Kraus et al. 2016;Falk 2021). In the case of bees and wasps, the microhabitat availability likely plays a role together with large trees functioning as landmarks, i.e. navigation points, for foraging flying insects. ...
Saproxylic insects are an important component of forest biodiversity; however, their ecological requirements are mostly studied on beetles, while other groups are less considered. Aculeate Hymenoptera provide valuable ecosystem services, and some rely on deadwood cavities. We studied cavity-nesting aculeate Hymenoptera using wooden trap-nests set in a heterogeneous partially rewilded woodland area in Central Bohemia, Czech Republic, and tested their nesting preferences in association with canopy openness, amount of deadwood, and the diversity of surrounding vegetation types. We used 100 trap-nests in five microbiotopes—forest edge, shady closed-canopy forest, open patches in closed-canopy forest, open-grown trees in wooded pasture, and shady groves in wooded pasture, over 2 years. We reared 824 specimens belonging to 26 species of saproxylic hymenopterans. We found no effect of microbiotope on total species richness and richness of nest parasites, but richness of nest builders was highest in forest edge and lowest in open-grown trees in wooded pasture. Species composition of hymenopterans was driven by a wider habitat context: despite the proximity of the habitats, the forest, especially closed-canopy patches, hosted a different community, dominated by wasps, than open wooded pasture. Moreover, open patches in forest differed in composition from the closed-canopy patches, suggesting that in production forests, the diversity of saproxylic hymenopterans may be limited by the overall low share of open canopy stages. Deadwood (amount and diversity) did not affect the saproxylic bees and wasps in any way.
Implications for insect conservation
Our results support conservation measures leading to diversification of the forest canopy and vegetation structure in order to support rich communities of saproxylic Hymenoptera, especially in protected areas.
... There was also a possible siting of one visiting Cowberry flowers near Loch Mallachie on 2 June 2022 (close to some artificial breeding stumps) but the specimen could not be captured for checking. The biology is summarised in Falk (2021). ...
... The biology and conservation requirements are summarised in Rotheray et. al. (2009) andFalk (2021). ...
The authors spent ten days (2-11 June 2022) recording insects in Strathspey and
the north-west Cairngorms in the Scottish Highlands concentrating on flies, bees and aculeate wasps. Twelve sites, which collectively provided a good range of the local habitats, were subject to fairly detailed one-day or half-day surveys. The survey work generated 1,561 records of 614 species/taxa. This included 539
species of fly (Diptera) and 23 species of bee. The raw data is presented within a
separate Excel spreadsheet (summarised in Appendix 3). The 2022 survey produced a list of 81 species with formal or provisional UK conservation statuses (see Table 1). Eleven of these are also on the Scottish Biodiversity List. A further three Scottish Biodiversity Lists species (without UK statuses) were also encountered. Visits by SF between 2013 and 2018 added a further 16 species with formal or provisional UK conservation statuses. The 2002 visit has so far produced two fly species new to the British list, the muscid Coenosia acuminata and the tachinid Gymnocheta magna. Several further fly specimens that cannot be matched with anything on the British list will be subject of further investigation. All the scarcer species are subject of species accounts in Appendix 1 which provide information on their ecology and status. Nine sites (eight covered in 2022 plus a further site covered in the 2013-2018 period) are subject of site profiles in Appendix 2.
... Nettle Urtica dioica are nectar-rich and very important to pollinators and several other Critically Endangered native insects (Falk, 2021;Wilson, 2021), though disliked by farmers as they reduce grazing area. There has been refinement of the condition criteria through the initial metric revisions, with the introduction of species richness thresholds for grassland types being particularly helpful to distinguish higher distinctiveness grassland. ...
Biodiversity net gain is a policy focus worldwide, acknowledging ongoing losses of biodiversity to development, and a commitment to offsetting any residual impacts on biodiversity elsewhere. At least 37 countries have mandatory offsetting policies, and a further 64 countries enable voluntary offsets. Offsets rely on credible and evidence‐based methods to quantify biodiversity losses and gains.
Following the introduction of the United Kingdom's Environment Act in November 2021, all new developments requiring planning permission in England must demonstrate a biodiversity net gain of at least 10% biodiversity net gain from 2024, calculated using a statutory biodiversity metric framework. The metric uses habitat as a proxy for biodiversity, scoring habitats' intrinsic distinctiveness and current condition.
We carried out a study of the metric's performance across England in terms of outcomes for biodiversity. We used generalized linear mixed models to regress baseline biodiversity units against five long‐established single‐attribute proxies for biodiversity (species richness, individual abundance, number of threatened species, mean species range and mean species range/population change). Data were gathered for species belonging to three commonly used indicator taxa (vascular plants, butterflies and birds) from 24 sites, including all terrestrial broad habitats except urban.
In baseline assessments, metric‐derived biodiversity units correlated with most plant biodiversity variables, but not with any of the bird or butterfly biodiversity variables used in this study. Plant species recorded in habitats with higher baseline biodiversity units had slightly more restricted ranges (slope −16.22 ± 1.52, p < 0.001) on average and had shown stronger past declines (slope −0.02 ± 0.00, p < 0.001) than those in habitats with lower baseline biodiversity units. Each additional baseline biodiversity unit was associated with a 1% increase in plant species richness (p < 0.01).
Synthesis and applications: Using the statutory biodiversity metric to define 10% biodiversity net gain without additional species‐focused conservation management is likely to translate into small gains for plant biodiversity, and negligible gains for birds and butterflies. We make specific recommendations to improve the metric's efficacy in achieving desirable biodiversity outcomes. Our results provide a valuable case study for other countries interested in developing metrics to support biodiversity net gain policies.
... Thanks are due to the Woodland Trust for commissioning this review and also to the various entomologists who provided information for the technical report (Falk 2021; www.britishecologicalsociety.org/applied-ecology-resources/ document/20210100953) on which this article is based. ...
A review of the flower-visiting insects that develop or nest in dead wood and tree wounds. Acts as a less technical summary of the Woodland Trust report publicy accessible on Researchgate here: https://www.researchgate.net/publication/349319059_A_review_of_the_pollinators_associated_with_decaying_wood_old_trees_and_tree_wounds_in_Great_Britain
... Dead wood in sunny locations with cavities and beetle holes can also be used as nesting sites for aerial-nesting bees such as Osmia, Megachile and Chelostoma species; also, aerial-nesting wasps such as Ectemnius, Ancistrocerus, Crossocerus and Pemphredon species (and the assorted cleptoparasites and inquilines associated with these such as chrysidid wasps and certain sarcophagid and anthomyiid flies). A review of pollinators associated with dead wood and old trees has recently been compiled by the author (Falk, 2021); Wet ground and shallow water -for the larvae of hoverflies such as Eristalis, Helophilus, Parhelophilus, Orthonevra and Chrysogaster species and some muscid flies such as Graphomya species; The nests of ground-nesting bees of wasps -for assorted cleptoparasites, parasitoids and inquilines such as cuckoo bees of the genera Nomada and Sphecodes, Bombylius beeflies and anthomyiids of the genera Leucophora. Such nests tend to be located in bare or sparsely vegetated dry ground fully exposed to the sun; Specific foodplants -for pollinators with phytophagous larvae such as butterflies and moths, sawflies, Cheilosia hoverflies, and certain anthomyiids of the genera Pegomya, Botanophila and Delia; ...
The report summarises four years of monitoring and surveying pollinators at Wytham Woods, Oxfordshire, a research wood owned and managed by the University of Oxford. The full data (in spreadsheet format) from active surveying and pan-trapping has been appended as supplementary data. More background to the project can be obtained from the Wytham Woods web page https://www.wythamwoods.ox.ac.uk/pollinator-monitoring.
The hermit beetle Osmoderma eremita is a native species for the Netherlands, with historical observations from the provinces of Overijssel, Gelderland and Limburg. After a 1946 sighting, it has not been recorded for decades. However, in 2004 a female was reported near Kerkrade in Zuid-Limburg, followed by two reports of close-by likely breeding trees. In 2020, a population was discovered in a hollow, dead willow tree in GaiaZOO in the same city. The hermit beetle is a habitat specialist that depends on large tree cavities filled with wood mold. The beetles can inhabit a tree for generations and hardly ever leave it, so it lives extremely hidden.
We estimate the chance that the species never disappeared from the Netherlands, but was present unnoticed for decades, greater than the chance that a new colonisation has taken place. The hermit beetle is protected under the nation Nature conservation act and the Habitats Directive, annexes II and IV. These came into effect at a time when it was assumed that the hermit beetle no longer occurred in the Netherlands. Now that the opposite is the case, efforts must be made quickly to ensure adequate protection of the beetles and their current and potential future
habitat.
This report first describes and illustrates the identification, biology and distribution of the species. Subsequently, the inventory and monitoring of the beetles and breeding trees are discussed. Given the hidden mode of life and sometimes inaccessibility of tree cavities, this brings many challenges. There is therefore a great need for more field experience and the further development of detection methods.
An initial exploratory inventory of more than 360 hollow trees in Zuid-Limburg has not yielded any new sites for the hermit beetle. However, this inventory – in which many other beetles and flies were found, including rare ones and two new to the Netherlands – has once again made it clear how valuable and important hollow trees are for biodiversity.
For a Habitats Directive species, a favorable conservation status should be pursued. This is determined by the status and trend in the distribution, population size of the species, the quality of the habitat and the future prospects. However, much is still unknown about the hermit beetle and its habitat in the Netherlands. This means that protection and (monitoring) research must be deployed simultaneously. Detailed research on potential breeding trees around the current population is urgent. The current populated tree is located outside a Natura 2000 protected area and thus a procedure will probably start for the designation of a new Natura 2000
protected area in Kerkrade.
Habitats Directive species have obviously been chosen because of their strong indicative value for endangered habitat types, so that protection of the species also protects nature in general (‘umbrella species’). This applies to a very strong degree in the case of the hermit beetle. In the recent past, the species occurred in particular in veteran trees, fruit trees in old orchards and pollarded trees, because these often have cavities. Protecting these, properly managing them and allowing them to develop or installing them are therefore useful steps and, given the many special species that occur in and near old and hollow trees, are also no-regret measures for biodiversity. In a more distant past, the hermit beetle was found in old, undisturbed forest. This is the most original and potentially most species-rich environment for
large parts of the Netherlands, but unfortunately it has disappeared. The hermit beetle is extremely suitable for drawing more attention to the values of old trees and old forest.
This article outlines the history of the Pine Hoverfly, Blera fallax, at its only known British locations in the eastern Highlands of Scotland. Information is presented on the larval and adult biology and previous conservation and management work for this species is reviewed. The article focuses on recent efforts at captive breeding which seem to hold out the best hope for the continued survival of the Scottish population until the pinewoods on which it depends can return to a more natural state. The importance of multi-agency team-working and the involvement of local volunteers in the success of the project is also highlighted.
One of four sheets that explain how to manage important habitat mosaics for associated assemblages of Section 41 invertebrate species i.e. Species of Principal Conservation Importance in England. This one features wood pasture and other sites with concentrations of old trees plus the important features that these sites can contain such veteran trees, dead trees, stumps, detached dead wood, semi-natural grassland, heathland, woodland, scrub, hedges, orchards, wetlands, waterbodies, tall herb, bramble, nettle beds, Ivy, grazing stock, dung and wild vertebrates. These sheets were published by Buglife with sponsorship from Natural England and were written by Steven Falk.
A comprehensive guide to the bees of Great Britain, Ireland and the Channel Islands covering all 275 species on the British list in 2015. The book can be purchased from most of the larger natural history book suppliers. 432 pp. Bloomsbury British Wildlife Field Guides. ISBN: 978-1-910389-02-7 (hardback), ISBN: 978-1-910389-03-4 (paperback).
The species of Diptera, Coleoptera and other insects present on an oak Quercus robur tree with copious basal white sap exudations were recorded over a seven-year period. Six species of Diptera were recorded feeding on the sap as both adults and larvae, 24 species as adults only and four species as larvae only. Nine other species, while not observed to feed on the sap either as larvae or adults, appeared more frequent on or around the tree than other trees nearby. The assemblage of flies attracted to the tree differed markedly from that described in the few other such studies reported, even those investigating white sap exudations on oaks in England. Oviposition was observed in Ferdinandea cuprea (Scopoli, 1763), Volucella inflata (Fabricius, 1794) and Phaonia laeta (Fallén, 1823): these species laid their eggs on bark some distance away from sap exudations. Larvae of F. cuprea were observed leaving sap exudations in the presence of Bioblapsis polita (Vollenhoven, 1878) (Ichneumonidae, Diplazontinae), an obligate parasitoid of Ferdinandea species. The tree attracted numerous insect predators including the hornet, Vespa crabro Linnaeus, 1758, three other species of wasp and several beetles, as well as insectivorous birds. Five beetles known to be sap exudation specialists were recorded, together with the endangered staphylinid Velleius dilatatus (Fabricius, 1787). Altogether eight nationally rare or scarce beetle and fly species, and a rarely recorded ichneumon, were found, confirming the importance of trees with sap exudations for insect conservation. The tree was of particular conservation significance within the context of Devon; three of the species recorded are not currently known from any other sites in the county (one beetle, one fly and one ichneumon), and four are known from only one other site. Trees with sap exudations should be valued and protected.
This book provides an introduction to the the hoverflies (Diptera, Syrphidae) of the British Isles. It covers all genera but only 60% of the fauna, and was designed as a companion to the monograph (Stubbs & Falk, 2002). It is extensively illustrated with close-ups of features that are important in making firm identifications. Additional information is provided on hoverfly ecology and collecting techniques, legislation and recording hoverflies. A complete systematic list is included for the time of publication - this is now somewhat out of date with new additions to the British fauna.
Originally published in 2013, it was substantially expanded for the second edition in 2015.
We present a key for the identification of males and females of 62 species of flesh flies (Diptera: Sarcophagidae) occurring in the British Isles, following the addition of several species to the British and Irish checklists in the last few years. Footnotes with characters for identification are given for an additional two (2) recently discovered species still awaiting publication, whereas a third species, Sarcophaga (Liosarcophaga) tibialis Macquart, 1851, known only from a single record from the 1970s, is not included. The key is based on the study of approximately 10,000 specimens held in the research collections of the Natural History Museum, London and is supplemented by colour photographs of diagnostic characters. The key allows for the identification of all males and 88% of females, the latter without the need for any special preparation or dissection of specimens. Emphasis is placed on characters of the external morphology not requiring a full dissection of the specimens, with the objective of maximising identification accuracy and reaching a wider user base for application in ecological studies, biological recording and forensic investigations.