Introduction

Norfolk is blessed with some wonderful sand dunes around its coast, from the vast expanse on the north coast, notably between Wells and Holkham, to those at Winterton, Horsey and North Denes on the east. We don’t get to visit these areas as often as we’d like, being dependent on the vagaries of public transport (with time consuming circuitous routes) and occasional lifts from friends. Cycling to Wells-next-the-sea and renting a holiday cottage for a week enabled us to explore more of the north coast.

These coastal areas are a magnet for visitors and locals alike and can sometimes become rather over-run, especially in the height of summer. It is easy enough to get beyond the crowds though by following the various paths and tracks that lead through the dunes, being mindful of any areas fenced off for nesting birds and taking due care not to cause any undue damage to the delicate dune vegetation.

Coastal sand dunes are challenging places for organisms to live in, the salt from sea water being one of the most obvious hurdles to deal with. Sand dunes are divided into three main categories. First are the sparsely vegetated embryonic dunes at the edge of the beach where the roots and rhizomes of Sand Couch and Marram grasses begin to bind the sand together. Then come the familiar yellow dunes characterised by thick clumps of Marram interspersed with bare sand. Finally, there are the more stable grey dunes further inland which support a variety of flowering plants and lichens.

The seaward edge of the dunes regularly gets inundated with salt water and storms constantly shift the sands around making life a difficult prospect for many creatures. Even in the more sheltered areas of the grey dunes further inland erosion still occurs from the actions of Rabbits and also human visitors. Blow outs by strong winds are also a common enough occurrence here. All in all, sand dunes are a hard place to exist in.

The dunes systems of the Norfolk coast support some wonderful invertebrates, many of which are very much dune specialists with several of them being quite rare or restricted in their distribution. Many of these are found within the stable grey dunes with their covering of specialist plants and lichens while others are at home within the dense clumps of grasses in the yellow dunes. Some of the rarest invertebrates are found right along the seaward edge amongst the shifting sands of the strand line. Over the last few years, each visit we have made has gradually yielded a growing number of these interesting creatures.

Beetles

There are so many species of beetle (Order Coleoptera) in the world that the evolutionary biologist J.B.S. Haldane said that if some kind of divine being had created all life on Earth, then they must have been inordinately found of beetles to create so many. There are certainly a lot of them and many can be found around the coast. Some of these beetles, described as halobiont species, are adapted to live in high salt conditions and as such are only found at coastal sites including amongst the sand dunes of Norfolk.

The Dune Chafer Anomala dubia (Family Scarabaeidae) is a largely coastal beetle although we have encountered it inland on the exposed sandy areas of Roydon Common. It is a large beetle with various colour forms ranging from entirely dark blackish or brownish, usually with a metallic sheen, to fully metallic green or with just the head and thorax green with brown wing cases (elytra). Most individuals that we have seen are like the latter, with a generally dull metallic green head and thorax and brown elytra. Our first coastal encounter was at Horsey and we have also seen them at Holkham. The larvae feed on the roots of plants.

The small scarab beetle Aegialia arenaria is found along sandy coasts where it feeds on organic debris. It is in the same family as the aforementioned Dune Chafer but is a definite dune specialist, only found around our coasts. We found several crawling across bare sand between clumps of Marram at Holkham.

The wonderfully named Phaleria cadaverina can be found amongst Marram Grass at the seaward edge of dunes. It is one of the Darkling Beetles (Family Tenebrionidae) and is a strictly halobiont species. The larvae live in the sand feeding on dead plant remains while the adults are omnivorous, feeding on carrion as well as decaying vegetable matter. The adults have been recorded feeding on bird droppings and found under the corpses of gulls which perhaps accounts for their specific name.

Other halobiont beetles that we have found on the Norfolk coast are Phylan gibbus (another species of Darkling Beetle) and Hypocaccus dimidiatus. Phylan gibbus inhabits the yellow dunes where its larvae feed on buried decaying plant material. The flightless adult beetles can be found all year. They are largely nocturnal and scavenge for food in grass tussocks and under seaweed on the strandline. In hot weather they are sometimes seen above the surface, as was the case with the one we found at Holkham on an extremely hot day in July.

Hypocaccus dimidiatus (Family Histeridae) has been recorded from various coastal sites around Britain where it can be locally common. It is a predatory beetle whose larvae develop in decaying organic matter including carrion where they feed on the larvae of various flies. We saw at least three adult beetles around the decomposing corpse of a long dead seal in the dunes at Titchwell.

It’s always worth investigating a corpse for beetles; the seal cadaver where we found Hypocaccus dimidiatus also had a Necrobia violacea on it. These beetles are widespread and locally common throughout much of Europe and have a scattered distribution in Britain but are not restricted to coastal dunes. They are often associated with dry carrion and bones with both adults and larvae feeding on decaying matter as well as predating larvae of other insects. It is sometimes called the Blue Ham Beetle and can be a pest in stored food stuffs including smoked or dried meats including bacon, and aged cheeses. Necrobius violacea also infests bones, rawhides and dried fish and have been transported around much of the world earning it the alternate name Cosmopolitan Blue Bone Beetle. I think it is a rather attractive little beetle and was very pleased to encounter one.

Probably the most striking of the dune beetles is the Dune Tiger Beetle Cicindela maritima. Nationally it is a rare species and in Norfolk it is restricted to a short stretch of coastline around Titchwell on the north coast. It is vulnerable to storm surges that remove large areas of sand along the foreshore where it is found, which could explain its absence from other areas of the coast where the habitat seems suitable for it.

The Dune Tiger Beetle is an active hunter and can be seen running across the sand above the high tide line on sunny days. It also takes flight readily, especially at the approach of a curious naturalist! They leave a tell-tale trace in the sand (see photo above) when they run short distances although this is soon eradicated by the wind that seems to be constantly present when we visit. In hot weather, they are said to retreat into the edge of the dunes and bury themselves under the sand. We have had most luck in finding them in the mornings.

Flies

There are some wonderful flies to be found amongst sand dunes, several of which are parasitoids with fascinating life histories.

Gonia ornata is a Tachinid fly that is found mostly around the coast amongst sand dunes (Wales being a hot spot) but with a scattering of inland records too. Tachinid flies are all parasitoids whose larvae develop inside a living host. The four species of Gonia currently found in Britain all target the caterpillars of various noctuid moths. The caterpillar grows, sheds its skin and pupates seemingly as normal but all the while a fly larva is developing inside. Then instead of a moth emerging from the pupa out comes the adult fly, often much to the annoyance of a lepidopterist who collected the pupa hoping to rear an unusual moth.

In the UK, the rare Tachinid Germaria angustata is pretty much restricted to the Norfolk coast. It isn’t known for sure what species this fly is parasitic on but where it is found in Canada it is believed to target the caterpillars of the Coast Dart Moth (Euxoa cursoria subspecies wirima). In Britain the Coast Dart (Euxoa cursoria) is found around much of the coast including Norfolk in suitable habitats (i.e. sand dunes) but is listed as nationally scarce.

The Dune Villa Villa modesta is one of the Bee-flies (Family Bombyliidae), a group of parasitoid flies that mostly target solitary bees and wasps. Like the more well-known bee flies (e.g. Bombylius major), the female Dune Villa primes her egg chamber with sand particles which stick to the eggs. She then flicks the tip of her abdomen forward while hovering low over the ground, shooting out the eggs with their extra ballast making them travel further through the air.

Villa species are thought to be parasitoids of lepidoptera larvae although it has been suggested that Villa modesta may target Megachilid bees as well. At Holkham we have seen Villa modesta around the nest sites of Megachile leachella in bare sand but have also witnessed apparent egg laying into short vegetation away from any obvious bee nests.

The Dune Robberfly Philonicus albiceps is frequently found in sand dunes around Britain’s coasts. In Norfolk it occurs on both the east and north coasts and is also occasionally found inland on some large sandy heaths. It is one of our larger Robberflies (Family Asilidae) and preys on various flies, including other robberflies and it isn’t above a bit of cannibalism either. We once encountered numerous pairs ‘in cop’ in the dunes at Titchwell one July.

Robberflies mate end to end; paired Philonicus albiceps characteristically form a right-angle but the pairs we saw flew off conjoined and then landed rather awkwardly and ended up in a straight(ish) line, possibly causing some discomfort (the male looked to have a kink in the end of his abdomen). The female lays her eggs in the sand where the predacious larvae develop, feeding on the larvae of other insects.

The Coastal Silver-stiletto Acrosathe annulata (Family Therividae) is a really beautiful little fly. The male has fine pale silvery white hairs covering the body while the female is slightly drabber with dark annulations (rings) on the abdomen. The female lays her eggs in the sand where the larvae are predators on other invertebrates. They have a widespread, largely coastal distribution in Britain and we have seen them several times at Holkham and Horsey.

Solitary Bees

Many of the solitary bees found in Britain excavate their nest burrows in the ground, often using the hard packed soil of paths or exploiting banks and soft cliffs. For some bees, sand provides an ideal substrate to dig into with some species forming large nesting aggregations within sand dunes.

The aptly named Silvery Leafcutter, Megachile leachella, is our smallest and, arguably, most attractive leafcutter bee. When newly emerged, both sexes have brown hairs on top of the thorax but these quickly fade to pale grey which, combined with the pale bands on the abdomen, give them their silvery appearance. The female has white hairs under the abdomen (called the scopa) for collecting pollen. A distinctive character of the females is the paired pale marks on the top of the tip of the abdomen comprised of adpressed hairs, although these can become abraded in older individuals and disappear. Males have striking pale green eyes.

Megachile leachella can be found in most if not all of Norfolk’s sand dune systems where they can form large nesting aggregations. They characteristically emit a high-pitched buzz as they dart and are on the wing from June until September. Both sexes can often be found foraging on bramble flowers and females can be seen flying to their nests carrying pieces of leaf segment with which to make their nest cells.

Other flowers we have observed Megachile leachella on include Bird’s-foot Trefoil, Ragwort and Cat’s-ear. Watching the comings and goings of bees at their nest site is often rewarded with spotting one of their nest parasites. We have often observed one of the sharp-tailed bees Coelioxys spp around Megachile leachella nests. These striking black and white bees are cleptoparasites. A female Coelioxys seeks out the nest of a host bee in which to lay her own eggs which is why they are sometimes called cuckoo bees. On hatching, the Coelioxys larva feeds on the stored pollen and nectar thereby starving the host larva to death. Some cleptoparasite larva will kill the host larva before eating the pollen.

Megachile maritima is another leafcutter bee that is found, as its name suggests, around the coast although it also nests inland in Norfolk in the sandy heaths of Breckland and there are even records from around Norwich. It is a large bee and closely resembles Megachile willughbiella, the males both having expanded white front tarsi. Close examination is required to confirm identification. Records in Norfolk are from June to August.

The scarce bee Megachile circumcincta has been recorded from the dunes at North Denes in the past and there are also records from Holkham. I have never managed to find one and it has declined nationally as well as locally.

The Sea Aster Bee, Colletes halophilus, is a largely coastal species with a limited distribution associated with salt marshes where the females collect pollen solely from the flowers of Sea Aster to provision their nest cells with. I have also found Colletes halophilus inland along tidal rivers where Sea Aster grows on the muddy river bank. They often nest in the sea banks around salt marshes but they also nest in the dunes at Holkham where they are adjacent to a muddy, marshy area that supports Sea Aster and other saltmarsh plants. Colletes halophilus can be found from August into October.

Colletes cunicularius was recently found nesting in the dunes at Holkham. The English name for this bee is the Early Colletes, with the bees emerging in March or April when the females collect pollen from willows. They are quite dissimilar from other species of Colletes in that they do not have the pale bands of adpressed hairs on the abdomen that give them their characteristic stripey appearance. Colletes cunicularius can easily be mistaken for one of the Andrena mining bees.

Until very recently, Colletes cunicularius was a scarce species found almost exclusively amongst sand dunes at only a few coastal sites in Britain. A large inland colony was discovered in Norfolk in the Brecks in 2015. In the last few years the species has suddenly started turning up in other locations, both in Norfolk and elsewhere in Britain. Whether these have spread from existing UK colonies or represent colonisation from Europe is not known.

Butterflies and Moths

The Dark Green Fritillary (Speyeria aglaja) is very much a coastal butterfly in Norfolk although in recent years there have been sightings inland. It is a fairly large and striking butterfly with the typical orange and black markings of many of the other fritillaries on the upper surface of the wings. The underside of the hindwing gives the butterfly its English name, being suffused with green and also bearing a number of large silvery white spots. It is a fast flyer, on the wing from mid-June to late August and can be difficult to catch up with to photograph. They have certainly given us the run around on hot sunny days.

In Norfolk, the Grayling (Hipparchia semele) is most reliably found on the east coast, especially at Winterton, although there are records from heathland sites inland. The upper surface of the wings is seldom seen as they habitually sit with their wings closed. The underside of the hind wings is a mottled pattern of browns and greys with a pale grey band across it. There is a black eye spot on the underside of the forewing which stands out briefly when the butterfly lands but is soon snapped down out of sight.

They can be very hard to spot when the wings are tightly shut hiding the eye spot, the cryptic colouration on the underside of the wings perfectly camouflaging them amidst the mosses, lichens and low growing plants of the grey dunes. The caterpillars feed on various grasses and the adult butterfly can be seen from late June until September.

There are plenty of interesting moths to be found in Norfolk’s coastal sand dunes but I have never had the opportunity to run a moth trap at any site. There is, however one rather magnificent beast that I had the rare privilege to encounter, the full-grown caterpillar of a Bedstraw Hawk-moth (Hyles gallii). The moth is mostly recorded as an immigrant species during the summer months, often at coastal localities but also inland. In Norfolk, there are scattered records of the moth across the county and there has been a small resident population on the north coast for a number of years. The caterpillars feed on bedstraws and willowherbs which are plentiful at Holkham in the grey dunes.

A number of otherwise coastal invertebrates are also found inland in the Brecks of Norfolk and Suffolk. Breckland is characterised by free draining, nutrient poor light sandy soils that are often covered with heathland or dry grassland vegetation, including some very rare plants. There is usually a lot of bare sandy ground too. It is therefore a habitat with many similarities to the arid grey dunes of the coast. The scarce Breckland Plume (Crombrugghia distans) finds both areas to its liking but we have so far only found it on the coast at Holkham.

Arachnids

Several species of spider are sand dune specialists and they can be found in Norfolk. Some of these are very rare and not often recorded. Of these, the one I would most like to find is the Sand Running Spider Rhysodromus fallax, a rare species found at scattered sites around the coast. It is extremely well camouflaged against the sand of the yellow dunes close to the foreshore. The other spider high on my wish list is the tiny jumping spider Attulus saltator which is found in the grey dunes. Both have been recorded on the north Norfolk coast but are difficult to find, or at least they are proving so for me!

However, all our dune searching did finally pay off when Jeremy spotted our first Steatoda albomaculata at Holkham. This spider is usually found inland on heathland where it inhabits areas with bare or sparsely vegetated soil, often colonising areas that have previously been burnt.

The blow outs in the grey dunes at Holkham seemingly provide the ideal conditions and it can be relatively common in places. On heathland, Steatoda albomaculata are said to prey mostly on ants and beetles that stray into their webs. The ones we observed at Holkham had taken up residence close to nesting Megachile leachella and had been snaring the odd bee or two as they came and went.

Another Holkham speciality we have been lucky enough to find is Marpissa nivoyi. Known as the Dune Jumping Spider, this tiny species has been found in the yellow dunes but is also known from a small area of marshy ground with reeds further inland. This seemed a better prospect for our search but it was a while before it yielded our quarry and then we only managed to find a single male.

The wolf spider Alopecosa barbipes is a scarce species of heathland and dry, sparsely vegetated grassland with scattered records across Britain. In Norfolk its stronghold is in the Brecks but it can also be found at the coast amidst the grey dunes at Holkham and Winterton. We have only managed to find this strikingly marked spider in the Brecks.

Arctosa perita aka the Small Sand Bear Spider has proven much more accommodating and has been relatively easy to find, and even poses for photos. We have found it several times amidst the embryonic dunes at Holkham on bare sand between patches of Marram Grass. It is well camouflaged but often gives itself away by running short distances across the bare sand. Despite being fairly common, it is always a delight to find one.

Arctosa perita is a largely coastal species, locally common and with a scattered distribution across Britain. It can also be found inland on heathland and other dry sandy places; we have even found it on our allotment in Norwich. Individuals found on heathland tend to be darker in colour than those found amidst sand dunes. The ones on our allotment are typically darker but equally well camouflaged against the soil.

Perhaps the best arachnid we have found in the dunes is the tiny pseudoscorpion Dactylochelifer latreillii, the Marram Grass Chelifer. All records for this species are from sand dunes in scattered locations around the coast, mostly on the east coast of England. It is found close to the foreshore amongst Marram Grass and Sea Couch-grass. Dactylochelifer latreillii is best searched for by looking under driftwood and other debris along the shore line or at the base of Marram Grass.

The first time we found one it was a lucky encounter on a windy day at Horsey with the poor little creature being blown along across the sand. Since then, I have actively searched for them at Holkham where I managed to find two at the base of Marram Grass close to the seaward edge of the dunes.

Pseudoscorpions have four pairs of legs like other arachnids and a pair of modified pedipalps that end in pincer like claws resembling those of a scorpion. Unlike scorpions they have no tail bearing a poisonous sting although some species do have poison glands in their claws. Pseudoscorpions are tiny, barely 2 or 3 mm long. They are active predators that hunt for small invertebrates.

When searching for pseudoscorpions you need a sharp eye for their first form of defence is to freeze instantly. They move very quickly and move just as fast backwards as forwards enabling them to rapidly get away.

The dunes can be inhospitable to humans too, we have been sand-blasted by strong winds on more than one occasion and suffered searing temperatures in the summer when our holiday to Wells coincided with the hottest temperatures on record in 2022 (reaching 38 degrees Celsius) which curtailed our ‘bug hunting’. There are still plenty more invertebrates for us to find amongst the beguiling shifting sands. Who knows what awaits us on our next visit?

Vanna Bartlett