Tag Archives: essex

Object of the Month – June 2023

This is the cast skin / exoskeleton (exuvia) of a dragonfly larva, found in Elsenham in August 2005. The shape of the eyes and the length (40mm) suggest it’s a hawker dragonfly, while the finder’s description of the adult dragonfly being green and yellow means it is probably a southern hawker, which are common in July and August.

Dragonfly exuvia © Saffron Walden Museum

These dragonflies spend 2 or 3 years as a larva, or nymph, living underwater, before coming above water to shed their skin and emerge as an adult.

Southern hawker dragonfly by Tom Wiersma, via Wikimedia Commons.

Dragonflies, like all insects, have a hard exoskeleton which does not grow with them. After hatching from an egg, dragonfly nymphs gradually grow into adults through a series of moults to shed their skin, which allows it to grow in size each time, emerging as an adult directly from the last moult.
The nymphs look similar to the adult, with a long body and six legs. Nymphs in the last stages of growth have wing buds that you can see on this specimen.
This method of growth, through nymphs with wings developing on the outside, is called incomplete metamorphosis.

This is different from other insects including flies and butterflies, which hatch as maggots or caterpillars. This is the larva of the insect, and it looks very different from the adult. The larva in these insects also has to moult to increase in size, but the final moult is different. It creates an inactive pupa (called a chrysalis in butterflies) where the final radical transformation into the adult takes place. This method of growth from larva to pupa to adult is called complete metamorphosis.

Visit the Museum to learn more about the two types of metamorphosis in the Discovery Centre, and take a closer look at two exuviae from our Malaysian stick insects.

Exuvia of female Malaysian stick insect © Saffron Walden Museum

Exuvia of male Malaysian stick insect © Saffron Walden Museum

Image credit:
Female Southern Hawker – Tom Wiersma, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons. Accessed 25.5.2023.

Identification – Fossil sponge in flint

Some flints do contain fossils, or look like whole fossils. Fossils inside the flints are often sea urchins, or cockles or other small shellfish. Sometimes, the whole flint looks like fossil, and this may be because the silica that created it was forced into a hollow space in the hardening chalk filled by a sponge. The silica fills the gaps in the sponge’s skeleton, and over millions of years, the skeleton itself can dissolve away and be replaced by other minerals. This skeleton is a fossil, and the flint fills the spaces left by the soft parts of the animal after they rotted away.

A grey, funnel-shaped fossil on a wooden surface

Typical funnel-shaped sponge, fossilised in flint. © L Hodgson.

The shape of this piece of flint looks a lot like a small sponge that lived on the sea floor, and was fossilised in flint as the thick mud solidified into chalk. It may have patterns inside it that show the structure of the sponge’s skeleton. The wiggly line around the widest part of the flint shows the top rim of the sponge and the rough texture of the line is the surface texture of the sponge preserved as a fossil.

More info on flint and chalk in Essex in this post from 2020. https://saffronwaldenmuseum.swmuseumsoc.org.uk/identification-flint-fossil-sponge/

Museum Society Talk – September

Object of the Month – June 2022

June’s object of the month celebrates the Lost Language of Nature project, with repair work to this hen harrier. With Lost Language of Nature, we want to hear your stories about wildlife and nature in your life, or rhymes, songs and sayings for all kinds of animals that you might have heard from parents or grandparents. For example, different old names across the country for hen harriers include Blue sleeves, Vuzz kitt, Grey gled, Furze kite and Goss harrier; or Ringtail for females, like this fragile mounted skin. Head to our website for more information https://www.swmuseumlearning.com/the-lost-language-project

This bird came to the Museum in the 1800s, and was taken from the area around Saffron Walden. Today, hen harriers only live in the north of England, north Wales, in Scotland and on Scottish islands, including Arran and Orkney.

Hen harrier on temporary base during conservation work.

Hen harriers today

Hen harriers are one of the UK’s most endangered birds of prey, with only an estimated 545 breeding pairs left in the country. They are on the RSPB’s Red List of endangered species in Britain, but listed as ‘Least Concern’ globally by the International Union for Conservation of Nature.

Work carried out by the RSPB suggests that over 2,500 pairs could survive in the UK. They live in open areas with low vegetation, like heather moors.

Between 2014 and 2019, the RSPB ran the LIFE project to learn more about hen harriers in Britain, their movements throughout the year and to understand why their numbers are so low. They tagged over 100 birds that they tracked using satellites, and found that some fly 1000 miles to spend the winter in Spain and Portugal. Not all birds do this though – the brother of one of these wandering birds always stayed within 50 miles of where he hatched.

In the UK, hen harriers are protected under Schedule 1 of the Wildlife and Countryside Act, meaning it is illegal to kill, injure or capture the birds, their eggs or nests, or even disturb the birds and their young while they are nesting. Despite this, the study showed that the numbers of breeding hen harriers fell by 24% (about one-quarter) between 2004 and 2016. In particular, the project monitored seven Special Protected Areas in parts of the country where land is managed for driven grouse shooting. In these seven areas, hen harrier numbers fell by over 80%, which suggests that there is deliberate human action to reduce their numbers in these areas.

References

https://www.rspb.org.uk/birds-and-wildlife/wildlife-guides/bird-a-z/hen-harrier/

https://www.rspb.org.uk/our-work/conservation/projects/hen-harrier-life/about-the-project/

https://community.rspb.org.uk/ourwork/skydancer/b/skydancer

https://community.rspb.org.uk/ourwork/skydancer/b/skydancer/posts/hen-harrier-apollo-bomber-migrate-1000-miles-to-spain

https://www.rspb.org.uk/our-work/conservation/projects/hen-harrier-life/best-places-to-see-hen-harriersnew-page/

Identification – Sea urchin fossil

Did you know we identify items for free? Whether it’s a rock from a field or a mystery something from the back of the shed, just bring it in to the Museum and we’ll take care of the rest! (If it’s too big or heavy, just send us an email with a photo).

This piece of flint with a strange marking on it was found in Wethersfield, near Braintree.

The flint nodule has preserved the impression of part of a sea urchin, or echinoid (pronounced ek-in-oid).

The shape you see is the external mould of a single plate of the echinoid’s ‘test’, or shell. When a sea urchin dies or is eaten, the test will often break apart into the individual plates.
Flint is formed from a silica-rich goo which hardens over time, and must have formed on top of this echinoid plate and taken its shape. The plates are made from calcium carbonate and this one will have dissolved away over time, leaving the impression behind.

The shape of the plate suggests it belongs to a species in the genus Cidaris. Saffron Walden Museum has a similar echinoid, Stereocidaris sceptrifera, fossilised in chalk, on display as no. 23 in the How Did They Live display in the geology gallery (below, top). In life, the club-like spines would have been attached to the plates. One of the Museum’s volunteers took this photo of a similar echinoid found at a chalk pit in Grays, Essex (below, bottom).

Fossil in chalk of the extinct sea urchin Stereocidaris sceptrifera, on display in the Museum’s geology gallery. SAFWM : 2020.42.23

The plate in the flint nodule (and the plates in the photos) is an interambulacral plate, which make up most the test of a sea urchin. They fill the space between the ambulacral zones, which are the areas where the urchin’s tube feet pass through the test. Tube feet are used for movement and to exchange oxygen and carbon dioxide with the water for respiration. Sea urchins have 5 ambulacra arranged in a star shape, showing that they are related to starfish.

The Natural History Museum has a good page showing the structure of a sea urchin test: https://www.nhm.ac.uk/our-science/data/echinoid-directory/morphology/regulars/intro.html

The British Geological Survey has an interesting page with good photos of similar fossil echinoids – look out for Temnocidaris (Stereocidaris) sceptrifera about halfway down, and Heterocidaris wickense at the bottom: https://www.bgs.ac.uk/discovering-geology/fossils-and-geological-time/echinoids/

Another link to the NHM with photos of Stereocidaris fossils: https://www.nhm.ac.uk/our-science/data/echinoid-directory/taxa/taxon.jsp?id=1115

Object of the Month – February 2021

Water voles are probably best known from the character ‘Ratty’ from The Wind in the Willows. Recently described as “Britain’s fastest, declining mammal”, they are making a comeback thanks to careful wildlife management and the return of a locally extinct predator – the polecat.

Water vole © Saffron Walden Museum.

Water voles are about the same size as a brown rat, but with a furry, much shorter tail, and small ears. Today, they are a semi-aquatic mammal, relying heavily on streams and rivers for food and shelter – they use their teeth to dig burrows into steep banks to shelter and raise their young.

Do water voles need water?

But it wasn’t always this way. They don’t show any of the usual adaptations for a water-based mammal, such as webbed feet and a ‘keeled’ tail (flattened sideways but taller top-to-bottom), both of which make otters very strong swimmers.
In the 1500s, rewards for hunting ‘rats’ may actually have referred to ‘water voles’ that lived entirely on land. Their burrowing habits and herbivorous diet would have made them an agricultural pest, which would explain the rewards paid for hunting them. Modern water voles are always found on waterways, so any hunting must have succeeded in wiping out fully-terrestrial water voles.

A population vole-ercoaster

In the 1990s and early 2000s, the number of water voles in the UK plummeted, making them Britain’s fastest-declining mammal. Surveys of water vole territories in Essex showed that 81% of recent territories were still occupied in 1990, but by 2005, only 7.5% of territories were still occupied in certain areas.
Such a drastic decline couldn’t just be down to habitat loss, and they are resistant to pollution – water vole colonies live in the banks of streams which run from landfill sites along the Thames estuary, and on rubbish-choked streams near Rainham.

Studies by Essex Wildlife Trust showed that crashes in water vole numbers closely followed local increases in the number the invasive American mink. These animals are not native to the UK, and became established after escaping or being released from fur farms from the 1950s onwards. Mink will hunt water voles in their burrows and in water, and a female can destroy a water vole colony in one breeding season. The water vole’s usual predators only hunt on land, and are too big to fit in their burrows.

American mink. © Saffron Walden Museum.

Essex Wildlife Trust began work in 2007 to control mink numbers in key water vole strongholds, allowing water voles to recover, and spread. In 2012, more areas were put under mink control, and water vole colonies were relocated from sites destroyed by development along the Thames and M25. Surveys in 2013 showed that these colonies had survived and spread, with several new colonies established along the river Colne and its tributaries.

Ratty’s new best friends

Since 2000, wildlife surveys have found an ever-increasing number of polecats, a native predator which had been extinct in Essex for over 100 years. Polecats were hunted to near extinction across the UK by gamekeepers, who treated them as dangerous vermin, and they were also easily caught and killed in rabbit traps, which fell out of use in the 1950s. Polecats have probably spread into Essex from a targeted release in Hertfordshire in 1982-3.

Natural Sciences Officer, James Lumbard, with the skin of a recenltly-mounted polecat. The polecat was brought to the Museum after being found dead at the roadside. Image © Saffron Walden Museum.

Otter © Saffron Waledn Museum. This otter is on view in the Victorian Museum Workroom display when the Musuem is open.

Informal tracking and recording also suggests that the return of polecats may be helping water voles spread and recover more quickly, by reducing mink numbers. The same is true for otters, which are now returning to Essex, after being declared locally extinct in 1986. Both of these animals are native predators that rarely hunt water voles, but will compete with the American mink for food and territory, and are also big enough to hunt or kill mink. There are no studies to confirm it yet, but it could be very good news for water voles, and wildlife-lovers across Essex.

References

Are the otter and polecat combining to reduce mink numbers? East Anglian Daily Times, first published 31 March, 2019. Accessed 29.1.2021: https://www.eadt.co.uk/news/business/rise-in-polecats-and-otters-hit-mink-2562736

Mammals of Essex by John Dobson and Darren Tansley, 2014.

Object of the Month – June 2020

June’s Object of the Month celebrates Volunteers’ Week. These fossils have been cleaned and recorded by two dedicated geology volunteers, helping to audit the thousands of fossils held in the Museum’s stores. The project is suspended at the moment, but we all look forward to getting back together when times are better.

These fossils are from the Red Crag layers, which are the reason Walton-on-the-Naze is famous for marine fossils. The sandy Red Crag rocks and fossils were laid down in the late Pliocene and early Pleistocene epochs between 3.3 and 2.5 million years ago, when a warm, shallow sea and bay covered most of Essex. The fossils have stained red-brown over time due to iron-rich water washing through the sandy rock.

The first fossil is a species of whelk, Neptunea contraria, which is still alive today (extant, rather than extinct). This species has an unusual left-spiral shell, hence the word contraria in its scientific name. Almost all species with a coiled shell have a right-hand spiral.

Neptunea contraria

Cardita senilis

Cardita senilis is a species of bivalve, a group which also includes oysters, mussels and scallops. These molluscs have a flattened body protected by two shells or valves joined by a hinge. A bulge near the hinge, called the umbo, is the oldest part of a growing shell, and is at the centre of the growth rings that can sometimes be seen on the surface.

Spinucella tetragona is an extinct species of predatory sea snail, in a group known as murex snails or rock snails. This species’ shells are highly ridged, but other extant species (such as Chicoreus aculeatus) have exaggerated and complicated patterns of spines on their shells, which makes them very popular with shell collectors.

Chicoreus a

Spinucella tetragona

Chicoreus aculeatus

Oyster: Ostrea species

Later Pleistocene fossils from Essex, such as the oyster, don’t really ‘belong’ here at all. They were brought south or churned up from older rocks by glaciers during the Pleistocene Ice Age, which lasted from 2.5 Mya to 12,000 years ago. They appear in glacial drift deposits left behind as the glaciers grew and shrank. This fossil of Chicoreus aculea is actually from the Jurassic period (201-145 Million years ago).

Identification – flint, fossil sponge

In Essex and south east England, almost every pebble on the beach and in gardens is flint. It’s a hard rock found in the Chalk, a soft, white, limestone layer that is up to 200m (600 ft) thick in north Essex and Cambridgeshire. In north west Essex, this chalk is between 90 million and 66 million years old and lies just below the soil, north of a line running from Stansted to Sudbury.

Diagram showing bedrock geology of Essex

Diagram showing the main bedrocks across a section of Essex. Chalk appears as the bedrock across northern Essex. Credit: reference 1.

Chalk started out as a thick mud on the floor of a tropical sea that covered most of Britain and north west Europe. This mud contained the remains of tiny sea creatures (plankton) which grew shells of calcium carbonate. When they died, these plankton and their shells fell to the sea floor to form a thick mud, which compacted into chalk over millions of years.

As it compacted, it squeezed out the seawater containing dissolved quartz, or silica (which comes from the skeletons of tiny sponges, a very simple animal).This silica was pushed out into gaps, cracks and burrows in the chalky mud to form nodules or layers of flint. These flints have a white outer layer (cortex), and are black inside. They can come in very complicated, bulging shapes, or with spikes, holes and cavities. Because of this, they can be easily confused with fossilised bones.

An irregular flint nodule with a white cortex. Credit: reference 2.

Some flints do contain fossils, often urchins, or cockles or other small shellfish. Sometimes, the whole flint looks like fossil, and this may be because the silica that created it was forced into a hollow space in the hardening chalk which contained a sponge. Sponges are very simple animals which live on the sea floor. They still exist today, and the earliest known fossil sponges are 580 million years old.

The silica fills the gaps in the sponge’s skeleton and, over millions of years, the skeleton itself can dissolve away and be replaced by other minerals. This skeleton is a fossil, and the flint fills the spaces left by the soft parts of the animal after they rotted away.
Sponges are hollow tube or cone shapes and have no muscles, stomach, brain or nerves. They are filter feeders that catch bacteria and microscopic plants & animals from seawater that flows through tiny channels (pores) in their body. Sponges are open at the top, and water currents flowing across the opening helps pull in water through the pores and remove it from the centre chamber, like wind blowing across a chimney.

Diagram showing water flow through a sponge's body

A simple diagram of a sponge’s body showing the pores in the sponge’s body, and the direction of water flow (blue arrows). Credit: reference 3.

A living sponge, showing the typical hollow tube shape. Credit: reference 4.

The first sponge below is preserved in chalk and is a typical funnel shape. Some fossils may have a textured ring around the top, showing the rough pattern of the sponge’s surface and pores, like in the second photo.

Figure showing typical funnel shaped sponge

Fossil of a sponge (Ventriculites species) that lived in the Chalk sea. This sponge attached to the sediment with its branching roots. © SWM.

Figure showing rim imprint of a sponge's body in flint.

A flint nodule showing the imprint of the upper rim of a sponge’s body. Credit: reference 5

References

Essex Bedrock, Essex Rock 1999. GeoEssex.org, retrieved 11:36, 24.4.2020
Adapted from: Porifera_body_structures_01 By Philcha – Own work, CC BY-SA 3.0
NOAA Photo Library reef3859 By Twilight Zone Expedition Team 2007, NOAA-OE. , Public Domain,
Flint rim print. flint-paramoudra.com, retrieved 11:47, 24.4.2020

Object of the Month – October 2019

This case is arranged to show which butterflies live in the Saffron Walden area today (left), and which are extinct (right).

These butterflies died off mainly because of changing land use in the 19^th & 20^th centuries. Butterflies such as the Adonis blue (1) and chalk-hill blue (2) prefer large areas of chalk wildflower meadow, grazed by sheep and cattle. However, much of this land was converted to crop farming in the 1800s and these specialist insects died off. Other changes, such as the end of coppicing in woodlands, removed the open wooded habitat that butterflies such as the grizzled skipper (3) thrive in.

Species like the purple emperor (4) and white admiral (5) feed on the sugary waste products from aphids (honeydew). Pollution from coal burning may have contributed to these butterflies’ extinction as the toxins could dissolve into the honeydew on the leaf surface.

However, 2019 has been a very good year for some impressive larger butterflies too, with lots of painted ladies (6) arriving in Britain from the Mediterranean as they migrate north. Protected roadside verges in Uttlesford also provide good chalk grassland habitat for species such as the small copper (7).

There is also some very good news for three ‘extinct’ species (green boxes in main image). The purple emperor (4) returned to Uttlesford about two years ago and has been seen in Shadwell Wood and Rowney Wood, two local Essex Wildlife Trust nature reserves. The silver-washed fritillary (8) was first seen again about five years ago and is now known from Shadwell Wood, Rowney Wood and Hatfield Forest. The marbled white (9) has also been spotted at Harrison Sayer and Noakes Grove nature reserves and along some protected roadside verges over the last two years. The return of these three species in protected areas of countryside and special habitats show just how important effective conservation efforts are in supporting our native wildlife.

You can learn more about how humans have affected local environments and wildlife, for bad and for good, in the Take Away the Walls exhibition until 3 November.
Find out how you can help local wildlife groups on the Discovery Centre noticeboard next to the stick insects, and in the Take Away the Walls exhibition.

The polecat comeback

Object of the Month – February 2019

The European polecat, Mustela putorius, was thought to be extinct in Essex since 1880 thanks to persecution from gamekeepers. The first modern sighting was in 1999 near Wendens Ambo and there are now numerous records from north-west Essex, though only from roadkill specimens.

A mounted polecat skin from 1842 and a polecat skull, also from the 1800s.

Continue reading →

Image credit: Female Southern Hawker – Tom Wiersma, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons. Accessed 25.5.2023.

Image credit:
Female Southern Hawker – Tom Wiersma, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons. Accessed 25.5.2023.