Seasonal Update (March 2023)

Daffodils (Narcissus spp.) are a quintessentially spring flower. - Credit: Marc Baldwin

Spring has sprung - meteorologically speaking, and here in the northern hemisphere, at least. (If you're reading this in the southern hemisphere: welcome to autumn.) This month gets its name from Martius, the first month in the Roman calendar until perhaps as recently as 153 BP, and is a nod to Mars, the Roman god of war. Martius represented the beginning of the season of warfare and involved many “new year” festivities in celebration.

Weather update

January ended and February began on a relatively mild note, with temperatures in low double digits Celsius across most of the country, not dropping far overnight. It remained dry, however, and windy at times. As we moved into the second week, we saw a brief pulse of cold air drop across the whole UK, with temperatures holding up in the sunshine during the day but dipping below zero at night, even on the south coast. This lasted for about a week, less in Scotland and northern England, before high pressure and mild air built back in across most of Europe. Consequently, by the second weekend and for the third week, daytime highs were surprisingly mild for the time of year, hovering around 12C or 13C (54F) across the south and reaching 16.4C in Wales and 17C (63F) in East Anglia - the seasonal average for mid-February is around 8C (46F). Scotland saw a rapidly deepening area of low pressure pass over towards the end of the third week, bringing some heavy rain and gale force winds.

Outside of the UK, we saw astonishing intensity of cold through Canada and the northeast USA in the first week of last month. Mount Washington in New Hampshire recorded a windchill of -78C (-109°F) on the 4th, which set the lowest windchill value ever observed in the USA (including Alaska). This freezing airmass was accompanied by sustained winds of 102 mph (164 km/h) and gusts up to 127 mph (204 km/h). South America, by contrast, saw a gruelling heatwave. Chile recorded some of its hottest days on record (temperatures into the low 40s Celsius / 105F+) with ferocious wildfires covering over 270 thousand hectares; the vast smoke plumes from the fires were visible from space. The 17th February saw hundreds of stations beating records of warmest February night: at least 91 stations in Germany and many others in Austria, Hungary, and Slovakia broke their records with overnight lows above 13C. In France, Le Vigan reached 24.5C (76F) on 19th.

Mid-February saw a pulse of exceptionally warm weather across much of Europe. - Credit: WX Charts

Temperatures reached high teens Celsius (mid-60s F) in Massachusetts and 27C (80F) in North Carolina during mid-February, which is unseasonably warm. Dawn on 10th February saw 16C (61F) in New York City. Further, historic warmth developed into the third week. Southern Japan also saw uncommonly warm temperatures, and Okinawa Prefecture reached record levels for early February, 27C (81F) at Iriomote Island, with nights holding at around 20C (68F). India experienced some extreme heat last month, too, with temperatures widely approaching 40C and even the mid-20s Celsius in the Shimla mountains, which recorded their warmest February minimum and maximum temperatures.

A state of emergency was declared in northern New Zealand during the middle of last month as Cyclone Gabrielle brought 101 mph (163 kmph) winds and 300mm of rain in 18 hours, causing mass power outages, evacuations and widespread damage.

News and discoveries

Many common frogs will have spawned by now. The earliest record for Hampshire was collected in the New Forest on 9th January. - Credit: Marc Baldwin

Canny canines. Scientists at the University of Veterinary Medicine Vienna in Austria have found that dogs can understand when their owners mean well, even if they don't get what they're expecting from them. In their tests, the body movements of dogs being offered a treat and having it either rescinded or dropped out of range by a “clumsy” human were tracked using eight cameras. The data showed that dogs exhibited signs of being happy and relaxed when the treat was dropped versus when it was withdrawn. The researchers suggest that dogs had more positive emotions towards the clumsy experimenter, which might indicate that they understand the person was willing, but just too clumsy, to give them food.

First Forest frogspawn. This year's PondNet Spawn Survey, run by the Freshwater Habitats Trust, has logged its earliest spawn on record for the New Forest. Amphibian and Reptile Conservation's senior ecologist Paul Edgar found the spawn in a shallow ditch in a New Forest inclosure on 9th January. This is a week earlier than normal for the Forest and represents the earliest spawn on record for Hampshire.

Forest friends. By studying a number of regenerating forests in Panama between 20 and 100 years after they were abandoned, a team of scientists have found that animals are key to the woodland restoration process. The research found that by carrying a wide variety of seeds into deforested areas, animals were an essential driver for the recovery of tree abundance and species richness.

Spiny senior. Results from the Danish Hedgehog Project have revealed the oldest known wild hedgehog. Between May and December 2016, more than 400 volunteers collected nearly 700 dead hedgehogs originating from all over Denmark, with a roughly 50/50 split from urban and rural areas. By counting the rings in sections of the jaw bones, the research team found that one male was 16 years old. In all, five animals reached at least 10 years, exceeding the previous longevity record of nine years.

Seasonal highlight – Bees; Britain's unsung heroes

The mere buzzing of a bee can conjure memories of lazy summer days in the garden, a spring/summer walk or picnic in the countryside. Most of us, particularly the keen gardeners among us, know that bees pollinate plants and produce honey, but too few people take an interest in the animals themselves. There has been talk in the media for many years that bee populations are declining globally, and that this means more than a lack of honey for your toast, but how much do we really know about the humble bee? What are the real ramifications of it no longer being a part of our countryside?

A bumblebee on a Dahlia. New research from Switzerland suggests bees can trigger flowers to produce nectar early by biting their leaves. - Credit: Marc Baldwin

Globally there are in the region of 20,000 different species of bee, and here in the UK we boast about 250. The vast majority (90%, or some 225 species) are solitary bees, with a further 24 species of bumblebee and only a single species of honeybee. Scientists group bees into two broad groups according to the types of flowers they have evolved to pollinate: short- and long-tongued bees. Each 'tongue type' has evolved mouthparts adapted for gathering nectar from particular constructions of flower. Britain plays host to four families of short-tongued bee: Colletidae (plasterer bees), Andrenidae (mining bees), Halictidae (sweat bees) and Melittidae (melitid bees). We also have two families of long-tongued bee: Megachilidae (leaf-cutting bees) and Apidae (many species including honeybees, carpenter bees and bumblebees). Within the UK it is bumblebees that are probably most encountered and are frequent visitors to gardens. We have five species that are found throughout the British Isles, and three with patchier distributions.

From A to bee

Bee sociality is a fascinating and complex subject. When people think of bees it is often the image of the swarm or hive that comes to mind, and this is despite most being solitary. Indeed, our only species to truly swarm (i.e., a large group of individuals moving en masse) is the honeybee (Apis mellifera). Despite not swarming, true bumblebees are nonetheless social insects, and form small colonies of related individuals to oversee the raising of the next generation. In late winter or spring (typically between March and May, depending on the species, weather and geography) the queen bumblebee emerges from hibernation and her first task is to find food to replenish her energy and trigger the development of her ovaries. While doing this, the queen will also be on the lookout for potential nest sites; suitable sites will be well insulated, warm (to speed up larval development) and near a good source of the high-quality pollen that is essential for rearing the first generation of workers.

Many bees will nest underground. This spoil heap surrounds the entrance of a tawny mining bee (Andrena fulva) nest. - Credit: Tico Bassie (CC BY-NC-ND 2.0)

Old mouse and vole nests, abandoned hedgehog hibernacula, or even disused birds' nests are all suitable sites for a bumblebee nest. Once a nest site has been found, the queen will build a small 'pot' from wax and fill it with regurgitated nectar - this will sustain her during periods of bad weather and while the first brood of workers are young. The queen busies herself collecting pollen for two or three weeks, creating a pollen lump on to which she lays her first batch of eggs; she may sit on her small, pearly white oblong eggs to incubate them and buzz her wings to generate heat and speed up their development. The eggs hatch after about 21 days.

Bumblebee larvae go through three life-stages (egg, larva and pupa) and several moults before they spin a cocoon out of silk produced from glands around their mouth and pupate, a process that takes approximately two weeks and results in the emergence of sterile female workers that look very similar to the queen but are considerably smaller. Pupation is a fascinating process during which the entire tissue structure is reorganised (in a similar manner to butterflies and moths) from a white maggot-like larvae into the fully segmented, 'haired' and winged fully-grown adult bee. The newly-pupated workers hang around the nest for a day or two drying off before they can fly. (During this period, the colour develops from a very pale cream/white and the wings stiffen.)

Once dry the workers head out to collect food; they collect both pollen, which is used to feed the next brood, and the nectar that is used to feed the queen and other adults. While the workers are away collecting food, the queen turns her attention back to laying eggs, nurtured by some of the smaller (often wing-deformed) workers that never left the nest, and the colony grows. How large the colony grows depends on the species and how much food is available in the area. Bumblebee colonies vary in size from about 30 to 450 workers, although many do not grow larger than about 150 individuals. Honeybees, by contrast, form much larger colonies with hives containing up to about 80,000 bees.

The production of workers in honeybee hives is of particular interest. Normally, the bees are assigned jobs based on their age (some forage, others tend to the young, some defend, others are engaged with housekeeping), but if the hive runs short of a particular type of worker more can be produced by controlling the incubation temperature. Raising the temperature of the cell to 35C (95F), rather than the normal 34C (93F) produces bees that are more inclined to prefer foraging jobs to ones involving housekeeping. So, the incubation temperature can control how eager, or reluctant, a bee is to change jobs according to the need of the hive. The temperature of the hive is maintained by bees of all ages vibrating their abdomens; they can uncouple their wings from their muscles, allowing them to use the muscles without moving their wings. When called to do so, they can heat up their body temperatures to 44C (111F), about 16C (9F) hotter than normal, to help heat the hive.

The honeycomb of the honeybee, showing larvae. - Credit: Susy Morris (CC BY-NC 2.0)

Initially the queen produces female workers but, later in the year, males and new queens are produced. Male bumblebees have a single purpose in life, to mate with eligible females, and so appear only at specific times of the year. Males are produced from unfertilised eggs (so they only have a single chromosome set), while females are produced when eggs are fertilised. This means that the queen can control the sex of the workers she produces according to whether she releases sperm (stored in a specialised pouch called a spermathecal, from matings last summer) or not. It appears that males start being produced as the queen essentially runs out of sperm and signals the beginning of the end for the colony because, once male eggs are laid, no more workers are produced.

Once unfertilised (male) eggs have been produced, any fertilised eggs laid are raised as new queens. The process by which queens are produced isn't clear for all species. One early suggestion was that as the number of larvae produced tails off during the summer, the workers aren't spreading the food so thin, and it is these better nourished larvae that develop into queens. Another suggestion is that the queen stops releasing the pheromone that tells the workers to raise workers once males are produced, and this results in any subsequent fertilised (female) eggs being raised as queens.

Among honeybees it appears that workers select some female larvae to which they feed a special protein-rich secretion called royal jelly. The protein royalactin is found in this jelly and triggers the larvae to develop ovaries and grow into queens. These new queens emerge from the nest and mate before heading off to feed up and look for a suitable hibernation site. Similarly male bumblebees leave the colony and never return, spending their days feeding and mating and their nights in torpor under flower heads and tree branches.

While the queen is in the colony she maintains her dominance over the workers, ensuring that they devote all their efforts to tending to her and her eggs. It seems that both a pheromone and direct aggression (head-butting and leg pulling) are used by the queen to maintain dominance over her workers and generally to prevent their ovaries developing - that said, workers can, it transpires, lay unfertilised eggs and one study of buff-tailed bumblebees found that about 10% of males were reared from eggs laid by workers. The workers will also feed the queen.

Sugar, oh honey honey

While many bee species produce something like honey it is not quite what we might recognise as honey and, at any rate, without a large colony to support, solitary and bumblebees don't typically produce very much of it. Indeed, it is only the honeybees that produce the honey we know and love on a commercially harvestable scale. Honey is produced by the hive to act as a food source and an average hive requires about 11kg (25 lbs) to see it through the winter; many commercial hives will produce closer to 27kg (60 lbs).

Bees tending honeycomb. - Credit: Robert Schmidt (Public Domain)

Having drunk their fill of nectar honeybees return to the hive and regurgitate it for the other workers, who similarly eat and then regurgitate it. This process of successive regurgitation causes the nectar to be mixed with enzymes (particularly one called invertase) that break down the long-chain sugar sucrose into the short-chain sugars fructose and glucose (in other words they partially digest it), which gives the final honey its sweet flavour. After the final regurgitation the honey is put into special wax cells in the honeycomb and the worker bees fan the cells with their wings, causing the moisture to evaporate and the honey to thicken. Once the honey has reached the appropriate consistency (about 17% water), the cells are capped with wax. The honeycomb will be opened when the bees require the food, particularly during the winter months when it is too cold and there are too few plants around to forage.

Bees in trouble

Early naturalists in Britain seldom saw a need to record bumblebees because they were considered so common, and it wasn't until relatively recently, when a project mapping bumblebee distribution using data collected up to 1976 suggested that these insects weren't as widely distributed as first thought, that a Biodiversity Action Plan was formulated, with five species added to it, and the Bumblebee Working Group was established to look at the status and conservation of bees in Britain. In the UK, in the last 70 years, two species of bumblebee have become extinct and six of the remaining 24 are listed as endangered.

A honeybee visiting lavender. - Credit: Marc Baldwin

It is widely considered that the replacement of hay meadows and pastures with arable monocultures, the decking/paving over of gardens, manicured lawns, and the increased use of pesticides (both in farmland and gardens) have all contributed to the decline of our bees. Among honeybees the problem has been particularly noticeable, with entire colonies disappearing. One estimate considered the number of colonies failing to survive the US winter in 2011 had risen from an historical average of about 10% to 30%; across Europe, hive losses are running at about 20% per year.

In 2006, the mysterious disappearance of honeybee hives was given the name colony collapse disorder (or CCD for short) and, since then, a great deal of money and research has been directed at searching for its cause and solution. CCD has been recorded across large parts of North America and a similar phenomenon documented in Belgium, France, the Netherlands, Greece, Italy, Portugal, Spain, Switzerland, Germany and Northern Ireland. In the UK, the British Beekeepers' Association reported that the honeybee population dropped by 30% between 2007 and 2008, although they didn't consider this a result of CCD, instead blaming a combination of wet summers, pesticides and the varroa mite parasite.

Pesticides have been widely implicated in the loss of bees, particularly a group of neuro-toxic chemicals (similar in their structure to nicotine) called neonicotinoids developed during the 1980s and 1990s. For the last decade or so, neonicotinoids have been implicated in the collapse of bee colonies and a reduction in farmland bird numbers (fewer insects = fewer birds). Unfortunately, there is no clear link between pesticide use and CCD, although there is a growing number of studies suggesting that some neonicotinoids (particularly one called imidacloprid) can impair bee immune systems (making them more susceptible to parasites and diseases), disrupt their memory and navigation (meaning they're more likely to get lost), cause hives to produce significantly fewer queens, and cause general neurological disorders.

A world without bees?

Few people would argue against the notion that bees play an important part in pollinating the plants in our garden. Albert Einstein is widely quoted as saying something along the lines that 'if bees disappeared from the planet, man would have only four years to live'. There is actually no evidence that he ever said this, but it is an enlightening statement that elucidates the importance of bees.

The United Nations Food and Agricultural Organisation estimate that about 90% of the global food supply is provided by some 100 species of crop plant in 146 countries; half of these rely on insects to pollinate them, and most of this work is done by bees (with a bit of help from moths, butterflies, flies, beetles, etc.). Indeed, pretty much all the strawberries, blueberries, grapefruits, avocados, cherries, apples, pears, plums, squashes, cucumbers, raspberries, blackberries, macadamia nuts and dozens of others depend on the foraging activity of bees.

Bees are a hugely important pollinator of a wide range of plant species. Pollen is collected in specialised sacs called "pollen baskets". - Credit: Marc Baldwin

In 2010, the UN's TEEB programme, which looked at the economics of various ecosystems, calculated that it would cost US$ 190 billion per year if humans had to pollinate all the agricultural crops manually. Agroecologist Alexandra-Maria Klein at the University of Gottingen in Germany estimated that crops relying on pollinating animals accounted for US$ 1 trillion of the world's annual US$ 3 trillion sales of agricultural produce, and an assessment of blueberry fruit production in Michigan (USA) estimated that bees provided a pollination service worth US$ 124 million each year. We also have good examples of real-world situations where wild bees are absent and the effect this has on crop production.

In California, almond production is big business but the habitat in which the almonds are grown is not bee friendly. The almonds are shaken from the trees by mechanical vibrating clamps and left on the ground in neat lines to dry before being vacuumed up. Consequently, the ground has been stripped of all vegetation to make lining up the almonds easier. The lack of ground flora means that there are no bees and, consequently, the farmers have to hire in over a million hives (each with 40,000 to 80,000 honeybees) at about US$ 200 per colony per season - a total of US$ 200 million per season.

Bees are similarly absent from fruit orchards in Sichuan, China, this time owing to the deployment of pesticides back in the 1980s, so every spring some 40,000 people must climb ladders in the orchards and pollinate each flower by hand, using a paintbrush. The problem with manual pollination is not only that it is very labour intensive and expensive, it's also less efficient because bees are better at achieving an even distribution of pollen than a man with a paintbrush. Indeed, hand-pollinated fruit is often smaller, paler, with a poorer flavour and there may be less of it. The bees also help maintain the genetic diversity of crop plants by transferring pollen between species.

It is also worth pointing out that the loss of bees from our countryside has wider implications than a lack of honey for your porridge or having fewer fruits and vegetables in the shops to meet your five-a-day. Many of the plants that we rely on for medicines (e.g., for heart treatments, anti-cancer drugs, decongestants, blood pressure medications, wart treatments, herbal remedies, etc.) rely on bees to pollinate them. Beeswax has more than a hundred industrial uses (it's often used in pharmaceuticals to change the properties of fats and oils), honey is now showing great antibacterial applications, and many of the cereals we feed our livestock are pollinated by bees. Even if technology could step in and replace all that these pollinators give us, though, what a sterile place the world would be without the buzzing of bees.

I hope the following brief introduction gives you a new-found appreciation of these amazing insects and, if you're interested in learning more, I can highly recommend Tony Juniper's book, What Has Nature Ever Done for Us? and A World Without Bees by Alison Benjamin and Brian McCallum. You can also find out more on the Bumblebee Conservation Trust's website.

For a round-up of Britain's seasonal wildlife highlights for the first month of spring, check out my Wildlife Watching - March blog.

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