May 2015

The early spring flowers are well out now, and in common with most other places our garden is showing mostly yellow ones.  There are lots of daffodils, lesser celandines, some Forsythia, and some dandelions.  They all look wonderful until you look a bit closer and see that almost every flower has got tiny blue-black beetles inside.  They are pollen beetles and they are doing what comes naturally, eating pollen.

Pollen Beetles in Daffodil

Pollen is amazing stuff.  First of all, it is very, very small.  The smallest pollen belongs to the forget-me-not and it is only six microns in diameter – that is 6 thousandths of a millimetre.  (The largest, maize, is about 100 microns across and more easily seen.)  You would need a good microscope just to see the rough shape of the pollen grains of any plant.  If you wanted to see each grain in detail, then it would be handy to have a scanning electron microscope in your potting shed.  Pollen grains are the equivalent of sperm in the animal kingdom, and are what transports the male genes to the seeds of the plant.  As in the animal kingdom, each plant species wants to fertilize, or be fertilized by plants of its own species, and plants achieve this by making the pollen grains unique.  So each plant produces pollen grains that have a certain size, shape, and surface texture.  Only when a matching pollen grain lands on the female stigma does the stigma accept the pollen and allow fertilization to occur.

Pollen Beetles in Lesser Celandine

Different plants also produce pollen of different colours.  Yellow flowers, like the ones that the pollen beetles are so fond of, tend to have yellow pollen, and that is the sort of default colour.  But if you examine the pollen baskets of bumblebees as I am in the habit of doing you find many different colours – comfrey has pale straw-coloured pollen; red clover has dark grey, almost black pollen.  One of the most startling colours is that of Viper’s Bugloss which has very dark blue pollen.  Just occasionally, I have seen bumblebees with bright red pollen on their legs, but so far I have yet to see which plant they have collected it from.

Brown-banded Carder Bee on Viper's Bugloss

The equivalent to ‘man cannot live by bread alone’ in the insect world would be ‘insect cannot live by nectar alone’ and one feature of pollen is that it is rich in protein.  For most insects that eat pollen, it is their only source of protein.    There are three main groups of insects that feed on pollen – the bees, of course, including the bumblebees and the solitary bees I wrote about last month.  Then there are the beetles – not only pollen beetles, but there are a range of other beetles like the thick-kneed flower beetle and some of the longhorn beetles as well.  Another group – the second largest group after the beetles – are the flies (Diptera), though only a few of them are pollen feeders, the most conspicuous of these being the hover flies and the soldier flies.  But what about the moths and butterflies I hear you ask?  Well, in the main, the adult insects don’t feed on pollen, they only take nectar (and some of the moths don’t feed at all as adults).  Whilst their caterpillars may take a bit of pollen, they are probably more interested in your brassica leaves.

Peacock Butterfly on Buddleia

The plant and pollinator relationship is a neat one, they each get something from it, but the interesting thing about the relationship is that the four groups of insects mentioned above all evolved before the plants developed their showy flowers.  They developed flowers when the primary disadvantage of having their pollen eaten was outweighed by the advantage of having their pollen moved from flower to flower and plant to plant.  This happened about 140 million years ago when plants started to become more attractive to insects by evolving their colourful and scented flowers.  So without the pollinators, there wouldn't be such flowers – what a dull thought.

April 2015

On sunny days you may have noticed a few bumblebees foraging on the early spring flowers.  They are most likely to be the fairly large buff-tailed bumblebee, or the tree bumblebee that are well known for emerging early from hibernation.  Most other bumblebee species emerge a bit later.  However, this column is not about bumblebees, but about their lesser known cousins, the solitary bees. 

There are about 250 species of bee native to the UK – The honey bee, 24 bumblebee species, and 225 solitary bee species.  Probably the reason that many people don’t know about solitary bees is that many of them are very small – only a few millimetres long and look more like wasps.  The larger ones may also be overlooked, but for a different reason; they are furry and look like small bumblebees.   So this raises a couple of questions – how do you tell the difference between solitary bees, wasps, and bumblebees.

Yellow-legged Mining Bee - Andrena flavipes

The really telling difference between solitary bees and wasps is their diet.  Wasps get their protein from other insect species, whereas solitary bees are vegetarian and only eat pollen.  Sadly, however, both are partial to a quick slurp of nectar, so if you see one visiting a flower, you can’t be sure whether it is taking nectar, pollen, or both.  Fortunately, the female solitary bees tend to keep the pollen conspicuously around their bodies, some species on their legs and some species under their abdomen, and provided the pollen is yellow enough, it should be easy to spot. 

Tawny Mining Bee (female)

Telling solitary bees from bumblebees is a bit trickier, and the only positive way of doing it is to be familiar with a few species and their habits so that you can learn which is which.  If you have a flowering currant in your garden, it will almost certainly be visited by the Hairy-footed Flower Bee (Anthophora plumipes).  This looks like a small black bumblebee with yellow hairs on its hind legs where it collects its pollen.  Another one to look out for is the Tawny Mining Bee (Andrena fulva).  The females emerge in early spring and you will often see them cruising an inch or two above your neatly clipped lawn (yes, me neither!).  They are an unmistakable rich tawny gingery colour and they are looking for somewhere to nest.  The nest will be a neat straight hole between tufts of grass and it will be surrounded by a small volcano of excavated earth.

(Hairy-footed) Flower Bee - Anthophora plumipes

It is the habits of the solitary bees that set them apart from other bees.  Honey bees and bumblebees are social bees.  They found a colony of worker bees that will help to gather nectar and pollen to feed the growing brood.  Honey bees put aside nectar in the form of honey to see them through to spring because most of the colony survives the winter in the hive.  It’s a habit that beekeepers and the rest of us are grateful for.  Bumblebee colonies don’t live through the winter and once the workers have helped the queen to raise the male and female bees that will found the next generation, the colony dies off.  Only the newly mated queens survive the winter.  Solitary bees have no workers to help them.  When the female is fertilized in spring, she digs a hole – in wood, soft mortar, or earth, depending on the species – and then lays an egg at the bottom.   Alongside the egg she deposits a pile of pollen, and then closes off the cell before laying another egg, piling in more pollen, and sealing off the cell.  She will carry on doing this until the hole is full.  That year’s males and females then die off.  The following spring, the egg nearest the end starts to get warm, the egg hatches into a larva which eats the pollen, turns into a chrysalis, then the adult male or female emerges from the chrysalis, bites through the seal, and goes off in search of a mate.  Then the next egg hatches, and so on.  The material used to seal off the cells varies from species to species.  Many use mud, but if you see small semicircles cut out of your lily leaves then it is probably a leafcutter bee that uses the lily leaves to seal off each cell.

Red Mason Bee - Osmia bicornis

One way to attract solitary bees to your garden is to put up a bee hotel.  You are probably familiar with these which have bunches of short lengths of bamboo built into a wooden box.  These are ideal for solitary bees and if you put them less than six feet from the ground on a south or west facing wall, you are almost guaranteed to see the cells filling up.  This time of year is an ideal time to put them up as well.

The reason that you may want to put one up is that solitary bees are great pollinators.  If you look at your fruit trees or bushes when they are in flower you will see that they are being pollinated almost exclusively by solitary bees. So put up a bee hotel, enjoy watching the bees visiting it, and enjoy a bumper crop of apples.  Isn’t nature brilliant?!

For links to fact sheets about the species pictured visit -

http://hymettus.org.uk/information_sheets.htm