Pseudogonalos hahni – the fascinating life history of Europe’s only trigonalid wasp


If you have never heard of a trigonalid before, then you are not alone. It took me until yesterday to discover these wasps actually exist, and their life histories are absolutely fascinating!

The story begins back in July. While surveying a former coal tip in the county borough of Neath Port Talbot, South Wales, I collected a large wasp that looked somewhat reminiscent of an aculeate wasp (e.g. sphecid wasp). Using the book Solitary Wasps (Naturalists’ Handbooks) by Peter F. Yeo and Sarah A. Corbet as struggling to find a match, I soon discovered that this wasn’t a solitary wasp but instead some kind of parasitic wasp. Somewhat stumped as to what it could be, with it looking nothing like any parasitic wasp I had seen before, I turned to the power of the Twittersphere for answers. Posting a picture of the wasp on Twitter, I soon received several responses confirming the wasp’s identity as Pseudogonalos hahni – an apparently rarely collected wasp. And then the interesting bit began! Through some research, I discovered the incredibly strange biology of the species and thought I’d just have to share this with you invertebrate lovers.

Trigonalidae is a small family of parasitic wasps comprising little over 100 species worldwide. They are largely found in the tropics and subtropics, and only one species (P. hahni) occurs in Europe. Almost all trigonalid species are hyperparasitoids (parasites of parasites), attacking ichneumon wasps (Ichneumonidae) and tachinid flies (Tachinidae) that parasitise leaf-feeding lepidopteran or symphytan (sawfly) larvae.

The lifecycle begins with the trigonalid female, which presumably after mating, lays thousands of eggs on the leaves of herbaceous and woody plants during their short lifespan (believed to be 8 days at most). The microscopic eggs in turn are by chance ingested by leaf-feeding lepidopteran or symphytan larvae. This method of host ingestion is rather unusual amongst parasitoids and only evident in some tachinid flies. Once inside the herbivorous host, the trigonalid larva waits for the host to become parasitised (if it hasn’t already been parasitised). The trigonalid larva can stay viable within the herbivorous host for several months waiting for the host to be parasitised.

Once the herbivorous host is parasitised, the trigonalid larva searches within the body of the host for the ichneumonid or tachinid parasitoid larva, after which it develops as a hyperparasitoid. So essentially, trigonalids such as P. hahni need an herbivorous host (lepidopteran or sawfly larvae) to be parasitised by a primary parasitoid (ichneumon wasp or tachinid fly) before it can complete its development. How crazy is that! The likelihood of this sequence of events occurring to result in an adult trigonalid seems slim. The high fecundity of the female trigonalid (laying thousands of eggs) and the wide host spectrum, however, ensure that at least some progeny will reach adulthood every year.

The lifecycle of P. hahni centres around July in Northen Europe, coinciding with my sighting of the wasp on 20th July 2018. So next July, keep an eye out for large black wasps and you too could find this rarely collected wasp.

For further information on Pseudogonalos hahni, check out this recent paper available for download (FREE) at


Rare dandelion found on South Wales coal tip

With their bright yellow blooms and fluffy seed heads, dandelions are among our most familiar plants. By blowing their spherical seedheads, generations of children have helped make dandelions one of Britain’s most common plants. Often viewed as troublesome weeds, dandelions have many herbal uses and are an important early source of nectar and pollen for insects such as butterflies and bees. Perhaps surprisingly, the humble dandelion is not a single species, but hundreds of very similar micro-species. Incredibly, there are estimated 250 different species of dandelion in Britain!

During a recent guided walk led by Liam Olds (Colliery Spoil Biodiversity Initiative) at Cwm Coal Tips, near Beddau, Rhondda Cynon Taf, the botanist Dr Tim Rich noticed a lightly-spotted dandelion. A picture of this dandelion was sent to Prof. John Richards, who identified it as Bertha’s dandelion (Taraxacum berthae). Bertha’s dandelion is a rare British endemic and this discovery at Cwm Coal Tips is the first time it has been recorded in the vice-county of Glamorgan (VC41). Key identification features are the pale spots on the leaves, the long terminal lobes, the dark reddish purple ligule stripes and the glaucous, appressed bracts.

berthae Cwm Colliery 14May18 (15)

During a second follow-up visit, Dr Tim Rich found Bertha’s dandelion quite widely around the site, especially on the slightly disturbed, damp muddy sides of tracks where the soil was grey clay, and occasionally on dryer ground. A total of 32 plants were recorded widely around the site, though Tim notes that it is certainly more frequent than that. It therefore appears that Cwm Coal Tips are an important site for this rare dandelion that was only found in one out of six sites surveyed in Northern England and Southern Scotland in 2017.

Discoveries such as this show just how special coal tips are. On a daily basis, we continue to learn more about the unique flora and fauna that these sites support. I urge anyone with an interest in natural history to visit your local coal tip or colliery site – you will not be disappointed. My thanks and congratulations are sent to Dr Tim Rich for this amazing discovery.

Liam Olds
Colliery Spoil Biodiversity Initiative

Rare ground bug ‘new to Glamorgan’ from former landfill site and colliery

Drymus pumilio

Drymus pumilio – photograph courtesy of Dr Tristan Bantock

This year has been another successful year for the Colliery Spoil Biodiversity Initiative. Three years into our research to investigate the invertebrate fauna on coal tips and former colliery sites, we continue to discover species of local and national conservation importance. This year we have continued to work closely with Rhondda Cynon Taf County Borough Council – who have been the principal supporters of our research – while also developing a new relationship with Neath Port Talbot County Borough Council (who kindly funded the survey of several coal tips within their constituency).

In addition to surveying coal tips this year, we have taken the word ‘tip’ literally and have have had the pleasure of surveying a former landfill site. Trecastell Landfill Site, near Llanharry, is unrecognisable from its days as a working landfill. In the relatively short period since its closure, the site has developed an interesting mix of habitats including some rather impressive wetlands. Surveys of the site have revealed several species of ‘conservation interest’, the most recent of which is the rare ground bug Drymus pumilio (pictured above).


Trecastell Landfill Site – June 2017

Amazingly, Drymus pumilio is one of the rarest bugs in Western Europe. It is considered a rarity across Europe and is known only from the UK, Low Countries, France, Italy, Germany, and Poland. It’s scarcity, both in Britain and elsewhere in Europe, make it subject for particular concern. While there have been several UK records in recent years, there is concern that this species is heading towards extinction. For such a scarce insect, it is found in a remarkably wide variety of habitats. When it is found, records are mostly of a single individual or small numbers – as was the case here, with a single individual being found. In Wales, it has been recorded twice, with both records coming from the Usk area of Monmouthshire. The first of these finds were made by Stuart Foster on 4th Oct 1989.

It’s recent discovery at the former Trecastell Landfill Site is a new vice-county record for Glamorgan (i.e. the first time it has been recorded in Glamorgan). If finding Drymus pumilio for the first time wasn’t good enough, surveying of the former Maerdy Colliery (in the Rhondda) revealed another – the second record for Glamorgan. These discoveries highlight the importance of brownfield sites for rare and scarce species. These brownfield sites can take many forms including coal tips and colliery sites, landfill sites, road verges, quarries, industrial estates and more. The Colliery Spoil Biodiversity Initiative will continue to highlight the importance of brownfield sites for wildlife in South Wales in order to aid their conservation. We look forward to reporting on our other exciting finds in 2017 over the coming months.

Thanks for reading.

Liam Olds





Weekly Highlights: W/C 15th May

Despite poor weather conditions Monday to Wednesday this week, suitable conditions prevailed on Thursday and Friday allowing me to get outdoors. On Thursday I visited Trecastle Landfill Tip near Llanharry, while on Friday I visited Cwmaman Land Reclamation Site (reclaimed coal tip) near Aberdare.  Here are just a small selection of the days finds.


Microdon myrmicae/mutabilis – A scarce hoverfly of wet habitats such as valley mire, wet meadows, and wet heathland and moorland. The slug-like larvae are parasites in the nests of ants. 


Xanthogramma citrofasciatum (Barred Ant-hill Hoverfly) – A widespread but localised species strongly associated with grassland and open-structured scrub with ant hills of Lasius flavus. It is believed the that the larvae feed on ant-attended aphids within the nests. 


Bombus monticola (Bilberry bumblebee) – A bee of upland moorland areas of northern and western Britain, it requires a landscape mosaic with Bilberry-rich moorland as just one of the components. This is an iconic species of the south Wales valleys and coal tips. 


Bombus humilis (Brown-banded carder bee) – Once widespread in lowland Britain, this species suffered a substantial decline during the 20th century. South Wales is one of its national strongholds, and these bees are a familiar site on the coal tips of the south Wales valleys. It exploits a wide variety of different habitats. This queen was observed foraging on invasive Cotoneaster


Erynnis tages (Dingy skipper) – An iconic butterfly of colliery spoil tips, so much so that you’ll struggle not to find it! The Dingy Skipper is locally distributed throughout Britain but has experienced substantial declines in some areas. 

Scarce bee at Lady Windsor Colliery, Ynysybwl

Today I visited Lady Windsor Colliery in Ynysybwl in search of a potentially interesting bee spotted by local resident (and friend) Steven Murray. Looking at Steven’s pictures of a nesting female, it appeared to resemble the Cat’s-ear Mining Bee (Andrena humilis) – a scarce species listed as Notable B in Falk (1991) (now known as Near Threatened).

Andrena humilis is widespread but very localised in southern and central Britain north to Cumbria. It is found in a variety of habitats but is mostly found in heathland and coastal districts. Pollen is obtained entirely from yellow hawkish composites such as Cat’s-ear, Mouse-ear Hawkweed and hawk’s-beards. Adults fly from May to July and nesting usually occurs along footpaths. Further information is available on the BWARS website.

Following a grid reference given to me by Steven, I started my search for the nests. Thankfully, the nests were relatively east to find, situated on a footpath beneath a rather distinctive oak tree. I noted what looked like 6 nests, although after waiting for almost an hour, I could see no sign of activity.  I decided to try again later.

On my return an hour or so later, I spotted a female pocking her head out of her nest. After patiently sitting beside the nest entrance, I watched her emerge and head off foraging (see sequence below).

Female Andrena humilis emerging from her nest

Around 5-10 minutes, she returned with pollen-loaded legs. Catching her in a net, I had a closer look and confirmed the bee to be Andrena humilis.


Female in a pot for a closer look

I also observed several males flying around a female foraging on a yellow composite well away from the nesting area (see below), suggesting further nests may be present elsewhere on the site.


Female foraging on yellow composite

I would like to take this opportunity to congratulate Steven Murray on his excellent find. This is another exciting discovery for the coal tips of south Wales, and represents the second coal tip in Rhondda Cynon Taf supporting this scarce species.


Liam Olds

Colliery Spoil Biodiversity Initiative



Rare bee discovered on coal tips in the Rhondda Valleys


A pinned specimen of Andrena falsifica from Whitbarrow, Cumbria © Steven Falk

A rare bee, last recorded in Wales in 1967, has been discovered in the Rhondda valleys. The Thick-margined Mini-mining Bee (Andrena falsifica) is a rare and poorly understood solitary bee species with scattered records as far north as Cumbria. It has only been recorded in Wales on three occasions: at Tregarth, Gwynedd, in 1967 (recorded by J. Morgan) and at St. Donats, Vale of Glamorgan, in 1929 (recorder unknown) and 1932 (recorded by H. M. Hallett). In South Wales, it hasn’t been recorded for around 84 years!

But, what are solitary bees?

In Britain, we have around 270 different species of bee. The social bees (bumblebees and the honeybee) account for around one-tenth of that figure, the remainder of which are solitary. Unlike bumblebees and the honeybee, solitary bees do not live in colonies, produce honey or have a queen. Solitary bees live largely independent lives, building and provisioning their own nests without the help of a worker caste. These charismatic and highly diverse bees are readily overlooked, despite the valuable pollination service they provide. Solitary bees are fantastic pollinators, and it is said that a single red mason bee (Osmia bicornis) is between 120 and 200 times more efficient at pollination than a honeybee.

Solitary bees are highly diverse, and so are their nesting habits. The majority of British species nest in the ground, excavating their own nests. The appropriately named Mining bees (in the genus Andrena) are ground nesting species. After choosing a suitable piece of ground, the female mining bee begins excavating a nest by digging. After creating the nest, she provisions the nest with nectar and pollen, everything her developing larvae needs to grow and develop. Solitary bees do not tend to the young as they grow, as bumblebees and honeybees do.

Andrena falsifica

In Britain there are around 65 species of bee in the genus Andrena, making the mining bees the largest of our bee groups. Among these mining are the mini-miners (subgenus Micrandrena), which are among the smallest of our bees (with many often measuring just 5 to 7 mm in length). The rare mini-mining bee Andrena falsifica was discovered by Liam Olds (founder of the Colliery Spoil Biodiversity Initiative) as part of his ongoing research highlighting the important wildlife value of south Wales’ coal tips. Relatively little is known about this bee, although many records are from heaths and moors. It is thought to forage on a wide variety of flowers including a cinquefoil, dandelion, Daisy, Wild Strawberry, Germander Speedwell and umbellifers. The bee was found at three different Rhondda coal tips – Tylorstown Tip (‘Old Smokey’), Gelli Coal Tips and the reclaimed tips of Clydach Vale Country Park.

Image 2

Gelli Coal Tips – one of the sites supporting this rare bee in the Rhondda © Liam Olds

Commenting on the find, Liam said “The discovery of this rare bee is very exciting and highlights the importance of our coal tips. Over decades, our tips have been colonised by a wide variety of plants and animals, and many now support habitats and species of considerable local and national importance. This discovery is just one of many other rare and scarce invertebrates, lichens, plants and fungi that have been found on coal tips. Coal tips are not only important wildlife habitats, but are part of our industrial heritage and cultural identity and they need conserving. The Colliery Spoil Biodiversity Initiative will continue to raise awareness of the importance of coal tips for wildlife and people in an attempt to aid their conservation”.

Please follow the Colliery Spoil Biodiversity Initiative on Facebook and Twitter, and spread the word about the importance of coal tips (and other brownfield habitats) for wildlife.

If you would like any further information on solitary bees, check out Ryan Clark’s Guide to Solitary Bees in Britain. For further information on Andrena falsifica, visit Steven Falk’s Flickr page and the BWARS website.




Bees of Y Graig, Llantrisant (WARNING: this has nothing to do with coal tips)

With my growing reputation as the county’s resident ‘bee man’, I have been asked by Rhondda Cynon Taf Council to conduct a number of surveys in addition to my regular work on colliery spoil tips. One of the sites I’ve been asked to survey is Y Graig (or The Graig). For those that are somewhat familiar with the area, Y Graig is a mountain adjacent to the historic town of Llantrisant. The famous Billy Wynt tower (pictured below) is situated on the highest point of Y Graig. With a height of approximately 173m (568ft), Y Graig offers fantastic and far-reaching views across south Wales – a must-see if your in the area.


Much of the mountain is south-west facing, and a number of footpaths transect the site. With the majority of our solitary bees showing a nesting preference for south-facing slopes, Y Graig could potentially hold a rather diverse bee fauna. This, has however, yet to be explored…but that’s where I come in.

After a morning of report writing, I decided to take advantage of a break in the weather to ‘scout out’ the site. Despite the sunshine, it was rather breezy. After some time walking around and having only seen one species of solitary bee, I was beginning to feel as though Y Graig would be a failure on the bee front. On top of the mountain, it was far too windy so I decided to head back down. Walking down the footpath pictured below, I noticed some nesting Halictus rubicundus (Orange-legged Furrow-bee).


This seemed like a good spot so I sat and waited for more bees to come along. Not long after being there, a female Sphecodes monilicornis (Box-headed Blood-bee) appeared, the cuckoo of  Halictus rubicundus.


Sphecodes monilicornis (Box-headed Blood-bee)

Then, a female Nomada lathburiana (Lathbury’s Nomad) appeared. Nomada lathburiana is the cuckoo of Andrena cineraria (Ashy Mining Bee), a species which I also recorded at Y Graig.


Several Nomada flavoguttata (Little Nomad Bee) were also observed searching for the nests of their hosts (which are mini-mining bees) on this footpath – so 4 species in just this small area!


Nomada flavoguttata (Little Nomad Bee)

The bee species list continued to grow as I followed the path downwards. By the time I got back to my car (around 2 hours after setting off), I had 15 bee species on the site list (and I could have added several more if I was a bit quicker with my net!). Here are a few pictures of some of the other bees I observed. It appears that Y Graig is a good site for bees, and repeated visits throughout the spring and summer may well reveal a decent bee list (lets hope so).

Enjoy the pictures.



Andrena flavipes (Yellow-legged Mining-bee)


Andrena fulva (Tawny Mining Bee)


Andrena haemorrhoa male (Orange-tailed Mining-bee)


Andrena nitida (Grey-patched Mining-bee)


Bombus sylvestris (Forest Cuckoo Bee)


Nomada fabriciana (Fabricius’ Nomad)