Silverfish and firebrats

The use of the word ‘primitive’ often carries with it a sense of disparagement, an inferred inferiority and a sense that the object being described is not as advanced as perhaps it should be. When the term is used in a biological context it has a different meaning, albeit one that is still tarnished by the wider negative interpretation. Primitive organisms, at least those still in existence today, have a long pedigree but may (to our eyes) be of simple construction. Such simplicity, however, underlines that the organism has a body plan that works, a plan that has enabled it to survive through countless generations with little or no change.

The term ‘primitive’ is often used to describe the bristletails, a group of small, wingless and carrot-shaped insects with a long and ancient lineage. Included with these are two creatures that are somewhat less familiar to us now than they were a few generations ago: the silverfish and the firebrat. Of these, the silverfish is likely to be the one you have encountered yourself, a silvery fish-shaped invertebrate, just a few millimetres long that has simple long bristles on its head, with finer ones emerging from its narrow rear end. I occasionally come across them in the bathroom, where their wriggling fish-like movement further emphasises that these are something different and interesting. I remember finding them quite frequently as a child in the warmth of the airing cupboard, where the temperature and humidity was to their liking.

Silverfish are easily overlooked, their small size and nocturnal habits reason enough for them to go about their business unnoticed. As such, you will find little written about them in general books on insects, which is a shame because they are fascinating creatures with a highly ritualised mating display. In this, the male and female approach and touch one another with their antennae, periodically backing away as if unsure, before returning for further investigation. This behaviour, which may last for many minutes, is then followed by a chase before the two individuals come to a halt side-by-side, the male vibrating his tail against the female and then releasing a capsule full of sperm. The female will then collect this and use it to fertilise her eggs, of which there are many hundreds.

Related to the silverfish, but less commonly encountered today, is the firebrat. Brown in colour, and certainly less fish-like, the firebrat does best in bakeries, around furnaces and near the warmth of open fires. The widespread use of domestic central heating is probably the reason for its disappearance from most homes. Both species are regarded as pests, their liking for carbohydrates (including paper and textiles) means that they can damage a range of products.

Our smallest carnivore

A narrow blur of warm brown flashes across the road ahead of me. Low to the ground, like a vole that has been elongated, this tiny, cylindrical mass of energy is a Weasel. In an instant it is gone, a bounding leap takes it up into the verge and out of sight. This is typical of an encounter with our smallest carnivore, all too brief and wholly unsatisfactory. On those few occasions when I have come across dead Weasels, freshly killed by passing traffic, I have been surprised at just how small they are. Even the largest males only just reach 24 cm in length and weigh in at less than 200 g. More typically, the males weigh in at 125 g and the females 70 g.

The Weasel is to be found across most of England, Wales and Scotland but is missing from nearly all of our offshore islands and, importantly, Ireland. It does best where there are good numbers of its favoured small mammal prey (mice and voles) and is usually associated with the cover provided by hedgerows and old stone walls. Its small size, which opens it up to predation by larger predators, may be one reason why it tends to avoid more open habitats.

At this time of the year the males are extending their exclusive territories, presumably in an attempt to increase access to potential mates, which will result in a number of female territories being enclosed within the male’s wider range. Individual Weasels do not make their own dens but instead occupy those of other species (such as rats, mice and moles). The small body size is an adaptation, allowing the Weasel to hunt and pursue small mammal prey down into their tunnel systems. This small size also enables them to enter and raid bird boxes in times when small mammals are less abundant. They have also been reported to take young Rabbits (a not uncommon prey item for the larger males when young Rabbits are available), reptiles, amphibians and even earthworms.

Most young are born between May and July, remaining with the female for three months as an energetic family group, and an encounter with such a party can be an engaging experience. Weasels are naturally curious and it is possible to call them out from cover by imitating a squeaking sound like that sometimes uttered by their prey when in distress. Closer encounters sometimes occur when using live traps for small mammals. I have caught several over the years and will always remember the one that, on release from the trap, turned and berated me for several minutes before disappearing off into the undergrowth. What they lack in size they make up for in character.

Our smallest carnivore

A narrow blur of warm brown flashes across the road ahead of me. Low to the ground, like a vole that has been elongated, this tiny, cylindrical mass of energy is a Weasel. In an instant it is gone, a bounding leap takes it up into the verge and out of sight. This is typical of an encounter with our smallest carnivore, all too brief and wholly unsatisfactory. On those few occasions when I have come across dead Weasels, freshly killed by passing traffic, I have been surprised at just how small they are. Even the largest males only just reach 24 cm in length and weigh in at less than 200 g. More typically, the males weigh in at 125 g and the females 70 g.

The Weasel is to be found across most of England, Wales and Scotland but is missing from nearly all of our offshore islands and, importantly, Ireland. It does best where there are good numbers of its favoured small mammal prey (mice and voles) and is usually associated with the cover provided by hedgerows and old stone walls. Its small size, which opens it up to predation by larger predators, may be one reason why it tends to avoid more open habitats.

At this time of the year the males are extending their exclusive territories, presumably in an attempt to increase access to potential mates, which will result in a number of female territories being enclosed within the male’s wider range. Individual Weasels do not make their own dens but instead occupy those of other species (such as rats, mice and moles). The small body size is an adaptation, allowing the Weasel to hunt and pursue small mammal prey down into their tunnel systems. This small size also enables them to enter and raid bird boxes in times when small mammals are less abundant. They have also been reported to take young Rabbits (a not uncommon prey item for the larger males when young Rabbits are available), reptiles, amphibians and even earthworms.

Most young are born between May and July, remaining with the female for three months as an energetic family group, and an encounter with such a party can be an engaging experience. Weasels are naturally curious and it is possible to call them out from cover by imitating a squeaking sound like that sometimes uttered by their prey when in distress. Closer encounters sometimes occur when using live traps for small mammals. I have caught several over the years and will always remember the one that, on release from the trap, turned and berated me for several minutes before disappearing off into the undergrowth. What they lack in size they make up for in character.

Spring comes to Breckland

I am fairly certain it was the painter Eric Ennion who said that spring came to Breckland via its river valleys, describing how the first flush of green reached these riverside habitats long before it touched the open warrens and heaths. Ennion would have known; having spent many hours wandering the brecks and fens and sketching its wildlife he would have been in touch with the shifting seasons.

Now, in the first few days of spring, you can understand this sense of restricted emergence; flowering and bud burst are evident along the Thet and the Little Ouse but the open heaths and clear-fell continue to be brushed with overnight frosts that leave the long dead stems of last year’s growth erect and white. As a strengthening sun warms the land, so you sense that spring spreads out from the shelter of the river valleys to claim temporary hold on the surrounding land. The first Brimstone, the first buzzing queen bumblebee and the growing chorus of bird song that shapes the transition from slumber to reawakening. But as the sun slips back towards the horizon, the clear skies let that weak warmth steal away and the overnight frost return.

The still, bright days are uplifting, delivering a sense of optimism and joy, the dark days of winter now well behind us and a season of warmth and new life just ahead. The false starts of early March are gone and it seems certain now that it can only get warmer and brighter and more green with every passing day. Other inhabitants of Breckland have sensed the change as well; the cries of Lapwing and Curlew ring out from neighbouring fields and Brown Hares can be seen chasing one another, the females turning to beat away over amorous suitors and striking a pose worthy of any pugilist. There is a sense of expectation in the air and a feeling that things will now pick up pace in the scramble to make the most of the emerging opportunities that extra warmth and light provide.

The forest, however, seems to hold back the arrival of spring. The dark ranks of conifers remain brooding, their green no brighter than it was under the winter sun, and it is only the growing chorus of bird song that marks the changing season in this regimented, reluctant habitat. Many of the flowers that I associate with the forest will not flower until late in the summer and there are few broad-leaved trees to signal through a flush of new growth that things have changed. For now I will stick to the river valleys and leave the forest until later in the year, when it is claimed by summer migrants and blooms.

Rare visitor amid the throng

Each morning, the Siskin flock announces its arrival at the garden feeding station with a cacophony of twittering calls. Perched at the top of the neighbouring sycamore, the Siskins will soon drop down through the branches to the feeders below. Despite the busy appearance of the flock itself, the birds are initially reluctant to move from the security of their lofty position. Perhaps the uncertainty stems from this tiny urban garden being so different to the acres of conifers and riverside alders that these birds will have been using over previous weeks.

Siskins are winter visitors for most of us, moving into gardens from February or March once the crops of wild seed are depleted. Many will have come from breeding grounds further north but some, notably in the west of the county, may be local breeders from Thetford Forest. The arrival of the Siskins is predictable, even if their numbers are not, but this year they have been joined by unusually large numbers of redpolls, which intermingle with their more common cousins. Redpolls are small finches, generally off-white and grey in appearance, with a prominent red forehead and soft brown nape and back. When seen alongside other visiting birds, they are fairly obvious.

Our redpoll was thought to be a subspecies of the Common Redpoll until fairly recently, subtly different in plumage, voice and behaviour. However, during the 1990s it was discovered that our redpoll is actually a different species and, having been elevated to full species status, it was given the name of Lesser Redpoll. Understandably, with many of the bird books on our shelves pre-dating the ‘discovery’ of this new species, there is still a fair bit of confusion among more casual birdwatchers, not least because the Common Redpoll is no longer the common species here! Having said this, Common Redpolls do turn up in Britain but always in much smaller numbers; their breeding grounds are positioned well to the north and east of us, stretching across the birch forests of northern Europe.

This winter has seen both increased numbers of Lesser Redpolls at garden feeders and an unusually large number of Common Redpolls in the country. With the former fairly regular in the Siskins flocks doing the rounds of Thetford’s feeding stations it is perhaps not surprising that there has been the odd Common Redpoll tagging along as well. Several have been caught and ringed by BTO staff at the various feeding stations operated throughout the Brecks and I was amazed to see one here in the centre of town. A neighbour, and fellow bird ringer, had caught it in his garden, a wonderful thing to see and something that made my week!

Something of a mixed year for butterflies

The results generated by the various recording schemes for butterflies have started to appear over the last few weeks. Looking across these it is possible to establish an idea of how 2010 shaped up and it seems that many species benefited from the hot June and July weather, which followed on from a cold winter.

As I noted in one of last summer’s columns, the summer heat helped species like White Admiral, which were able to shorten the time spent as a mature caterpillar and chrysalis and so reduce the levels of predation, a key factor to determining the size of the summer generation. Other butterflies, notably some of our less common species, also did well, with the Silver-washed Fritillary delivering the big success story for East Anglia. It appeared across the region in good numbers, re-establishing itself at some sites after a long gap.

Many of our familiar species did less well, especially immigrants like Red Admiral and Painted Lady, numbers of which were both very much down on the 2009 influx that grabbed the headlines. Such short-term fluctuations are not cause for concern. Some species exhibit regular changes in abundance that are shaped by parasite populations. The Holly Blue, for example, has populations that cycle depending on how common a particular small parasitic wasp happens to be. When the Holly Blue enjoys a good year, this allows the parasite to do well, meaning that the levels of parasitism will be greater the following year; this, in turn, brings the Holly Blue population back down.

Being able to see longer-term trends is a key component for any attempts to conserve our butterfly populations. This is where systematic recording schemes, like the Wider Countryside Butterfly Survey, carried out by volunteers from Butterfly Conservation and the BTO (many of the BTO’s bird recorders revisit their survey squares to record butterflies for this survey). Less common species are monitored by coordinated counts at key sites, as is the case with the Silver-studded Blue monitoring that takes place on some of the Norfolk heaths. Volunteers provide a key role in this work, working in collaboration with researchers to keep tabs on these changing populations.

Most butterflies are fairly straightforward to identify, meaning that (with a little training) you can make a valuable contribution to the work of organisations like Butterfly Conservation. If you would like to get involved in some of the butterfly recording work taking place across the county, or simply want to find out more about Norfolk’s butterflies, then why not contact the Norfolk branch of Butterfly Conservation. Visit www.norfolk-butterflies.org.uk or contact Chris Dawson on 01603 545092 if you would be interested in helping with their Wider Countryside Butterfly Survey.

Some robust fungi

When you think of fungi you tend to think of the soft fruiting bodies evident throughout the autumn months, the mushrooms and toadstools of grassland and woodland. Yet there are fungal fruiting bodies that are more robust in nature and which can be seen throughout the year. Included in with these are the bracket fungi, hoof or plate-shaped structures that emerge at right angles from the vertical trunks of standing timber or from fallen wood.

Bracket fungi are seen by some as parasites and the destroyers of wood, but this attitude misses the point and devalues the valuable role that fungi play in the recycling of nutrients. The brackets themselves are the fruiting bodies, the only external evidence that a fungus is present within the timber (much as mushrooms and toadstools are the visible component of fungal systems lurking within the soil, leaf-litter and underground root systems of plants and trees).

The bracket is the means by which the fungus can distribute its fungal spores to colonise new sites. In order to gain access to these sites, the spores will typically have to gain entry through the protective bark, perhaps through a wound. As you can imagine, the chances of an individual spore, distributed as they are by the vagaries of the wind, encountering a suitable wound are remote. This is why so many spores are produced; for example, it has been estimated that a large Ganoderma bracket fungus might produce a staggering rain of some 20 million spores per minute steadily over a period of five months!

Many bracket fungi are associated with particular tree species – the already-mentioned Ganoderma species on Oak and Beech, for instance. Most trees in their middle and old ages probably host bracket fungi and some or our oldest trees support particularly scarce and localised bracket fungi. In these trees you often find that the fungal decay hollows out the heart wood, the living sapwood being confined to a narrow region between the decaying interior and the bark. Being hollow can be advantageous to an old tree since it lightens the load, reducing the amount of heavy deadwood, and increases the tree’s flexibility when it is windy. Interestingly, it was the younger-aged trees that were hardest hit by the 1987 gale in many of our oldest woodlands, the hollow cylinder trunks of the older trees better able to withstand the conditions.

The fruiting bodies of most bracket fungi are pretty solid and so it is unsurprising that few are deemed edible or worth the effort (though Sulphur Polypore was a faddish exception in the nineties, featuring in certain gourmet restaurants). Their robustness is part of their appeal, marking them out from the ephemeral mushrooms and toadstools.

Here be dragons

When seen under a binocular microscope it is clear that centipedes are fearsome predators, well armoured and with huge poisonous fangs. They are a group of invertebrates that I have taken an increased interest in lately because we are attempting to draw up a more complete list of the species to be found in the grounds of the Nunnery at Thetford, home to the offices of the BTO.

This list is something that we have been thinking about for a number of years and, thanks to an opportunity provided by one of our more competitive colleagues, it is something that we now how sufficient interest and momentum to deliver. There has always been light-hearted and competitive banter between staff at the BTO and those at the RSPB headquarters in Bedfordshire. The two sites have similarly long bird lists and it was this that prompted a challenge – which organisation could record the greatest number of different bird species on their headquarters site in 2011. It was easy enough to convince such competitive types of the value of extending the challenge across all taxa!

So here I am, extending my knowledge of centipedes by slowly working through identification keys and by counting legs and claws, working out the shape of microscope pits and by looking for projections on different body segments. I am sure that you would be able to describe a centipede; an elongated body of multiple segments, each with its own pair of legs. More flattened in shape and with fewer legs than a millipede, you’d recognise one without too much difficult. There is some variation around this basic structure, those that live in the soil tending to be smaller, more cylindrical, often blind and with more pairs of legs; those that are surface active with fewer legs and larger heads. Such differences allow you to get down to the family and then genus fairly readily but identifying the species can be more problematic. It is here that the microscope becomes an essential tool.

It is when you view any invertebrate under a microscope (or with a hand lens) that you really come to appreciate them. Features invisible to the naked eye take on magnificent solidity under the lens and you start to realise just how impressive (or perhaps terrifying) many of these creatures would be if they were scaled up to the size of a small dog or bigger. While many beetles and bugs would appear as benign and lumbering herbivores, the centipedes would be terrifyingly fast and efficient predators, chasing down prey and delivering a dose of immobilising venom. Some might consider it a good thing that our planet’s climate cannot support such large and fearsome versions of these familiar species.

Teacher teacher!

It is on those days when the first touch of spring-like warmth can be felt that many of our resident birds are spurred into song. Perhaps the most familiar and noticeable of these early springtime songsters is the Great Tit, whose ringing ‘teacher-teacher’ song can be heard from woodland, hedgerow and garden from February onwards.

With a broad black stripe running down his chest and widening to meet his legs, the male Great tit is arguably the most handsome of our tit species. This stripe plays an important role in Great Tit behaviour. While you and I might be able to distinguish between a male and female (her stripe is narrower and peters out about halfway down the belly), female Great Tits can detect subtle variation in the male stripe, which acts as a badge of social status. A male of high rank will make a better mate, providing access to more resources and so increasing the female’s chances of rearing a brood of chicks. Great Tits invariably have just the one brood a year.

Although the basic ‘teacher-teacher’ structure of the song is familiar to most birdwatchers, there are variations on this theme, with older birds tending to have a more diverse repertoire. One old male was found to use some forty different variations of the ‘teacher-teacher’ theme. The amount of song will be greater on warmer days and will increase as spring takes hold more firmly. Song output declines once the female begins incubating her clutch of eggs. Incubation does not begin until all of the eggs have been laid and the clutch is complete.

Interestingly, the female will begin to roost in the nest cavity from once the first egg has been laid. Although she sits on the nest she will not be generating sufficient heat to start incubation. This only happens once her brood patch develops. This is an area of bare skin, rich in blood supply and hot to the touch, that forms just before the clutch is completed. The combination of the brood patch and shifting patterns of time spent off the nest means that she can regulate the temperature of her clutch, keeping the eggs at 35.4 degrees C.

As if the effort of producing the eggs was not enough, the real work will begin once the eggs hatch and the chicks emerge. Each chick weighs just over a gramme when it emerges from the egg and it will increase to some fifteen times this weight when it is ready to leave the nest. One researcher calculated that the effort of feeding a brood of Great Tits was equivalent to a human parent bringing home more than 100kg of shopping every day for just over two weeks!

Wee-beasties

Woodlice are an object of childhood fascination for those fortunate enough to encounter them. For the majority of adults, however, woodlice belong to that great sweep of invertebrate diversity that is simply ignored for having no obvious impact on our daily lives. Even some of my colleagues, with a background in biology, did not realise that forty different woodlice species have been recorded outdoors in Britain, with a further 12 introduced species maintained inside horticultural glasshouses. Four of the species found outdoors are ubiquitous and can be found in very large numbers across Britain. Quite simply, woodlice are the most successful group of crustaceans to have colonised the land.

Woodlice are an essential component in the process of decomposition and nutrient recycling, feeding on a variety of partly decomposed plant material and even the flesh of dead animals. You might think, therefore, that they are rather efficient in this role. In actual fact, they have a rather inefficient digestive system; much of the material that they need passes straight through the gut. Like Rabbits, woodlice eat their own faecal pellets, although in this case they rely on bacterial activity prior to reingestion to get at the nutrients still locked inside.

The successful colonisation of the terrestrial environment has been possible through a number of adaptations. The most notable of these is a fluid-filled brood pouch which protects the young from drying out during the first weeks after hatching from the egg. The problem of water loss shapes other woodlouse features and behaviours. Woodlice have external pleopodal lungs, visible as tiny white patches on the underside of the body, which remain moist and facilitate gaseous exchange between the air and the blood. Nitrogenous waste is excreted as ammonia gas, another water-saving adaptation, and it is this that is behind the smell of urine that can be noted where large numbers of woodlice are found together.

The need to reduce water loss is also the reason why woodlice tend to be found in damp environments, either under dead wood, large stones, within leaf litter or within the soil itself. The choice of these different microhabitats also shapes variation in the basic woodlouse body plan. Those most tolerant of ‘drier’ microhabitats tend to be the larger robust species familiar to any child that has turned over a stone or broken off a piece of dead wood. Some of these species can role into a ball if disturbed. Others, known as ‘clingers’, clamp themselves to the substrate, while others still (known as ‘runners’) have a surprising turn of speed. Soil-dwelling forms are smaller, with shorter legs and one of these lives within ant nests. All in all they are a diverse and fascinating group.