July 2018

In a recent ‘Nature Notes’ I talked about seed dormancy and rattled on about tough seed cases and scarification.  It turns out that I was completely wrong – or at least that wasn’t the whole story.  Listening to ‘The Life Scientific’ on Radio 4 recently, I heard Professor Caroline Dean explain the genetic and molecular basis of vernalization, the process that tells the seed when it is spring.  It turns out that seeds have a gene that codes for a protein that keeps the seed in a dormant state.  Cold weather turns the expression of that gene off.  However, it turns the gene off only one cell at a time so that it takes several weeks to turn all the genes off and stop the production of the protein.  This explains why seeds don’t suddenly start to sprout when we get a warm spell in mid-December.  Once all the genes are turned off, then the seed has to wait for all the other conditions to be right – temperature, moisture, day length, etc. – before growing into what should then be spring.  Interestingly, plants grown in colder climates take longer for this process than warmer countries with shorter winters.  So if you take seeds from Sweden and plant them in Spain, they will still need  say 10 weeks of cold weather when the native Spanish plants of the same species need only four weeks.

In last month’s Nature Notes I spoke about how interesting it was watching the solitary bees nesting in our solitary bee hotels.  It turns out that we weren’t the only ones interested in them.  One day we went out to find short bamboo tubes all over the patio, emptied of their content, with a corresponding huge hole in the bee hotel above.  We suspected that a woodpecker had learnt that it wasn’t only crevices in trees that contained juicy snacks, but we were open to other possibilities until further evidence presented itself. 

Note that the box on the right is unoccupied, mainly because the tubes are too big.

We didn’t have long to wait.  A few days later we were rudely awakened at 5 in the morning by a loud hammering on the back wall.  Opening the back door scared the great spotted woodpecker away and saved the bees from further carnage.  We still have two more bee hotels that are so far unscathed but we are seriously considering building some sort of woodpecker-proof cage round them.

While I was looking up woodpecker damage on the internet (of course it has happened to others), I found another interesting fact about solitary bee hotels.  The majority of bees in our bee hotels were red mason bees.  These emerge in spring and will have laid their eggs and died long before the end of June.  However, another group of solitary bees – the leaf-cutters, which are summer nesters – have now emerged and are looking for nesting sites.  If a red mason bee has run out of eggs or energy or life before completely filling the nest hole, then the rest of that hole may be used by a leaf-cutter bee.  (If you find almost circular holes in the edges of your lily leaves, it will be leaf-cutter bees that have taken the bits of leaf to seal up their nest cells.)  The problem with this is that the red mason bees will emerge first and will have to eat their way through the leaf-cutter cells thereby killing their occupants.  Life is tough at the bottom of the food chain!

June 2018

May so far has been an unpredictable month weather-wise. Weeks of unseasonal hot weather, interspersed with normal temperatures and chilly winds.  But nature is still getting on with things – we have blue tits nesting in their usual nest box (they don’t seem to like the shiny new one), ‘our’ swallows have returned to nest in the carport, and the house martins have been surveying a property in our eaves (only surveying so far, no sign of nesting or laying).  There have been a couple of other welcome events in the bird world – a cuckoo has been calling from the trees behind us for a week or so but he seems a bit hoarse as though he’s been over-cucking.  Hopefully a mate will have survived the trip back from Africa so that he can give his syrinx (voice box) a rest.  While we were sat in the garden watching the sun go down one evening, we saw a barn owl carrying some prey across the field at the back from the Pannel valley direction into the trees behind the field. 

Barn Owl (Norfolk)

We’ve seen barn owls in Pannel valley before, but never this far over.  The direction it was flying suggested that it has a nest in the trees behind the houses on Pett Road.  I’d be interested to know if anybody else has seen it.

We have also been fascinated by the activities of some other nesters – solitary bees.   These have been making use of our solitary bee hotels and have been working hard for a couple of weeks.  The first thing to attract our attention was a small swarm of male bees gathered round one of the hotels.  It was a very small swarm – never more than half a dozen individuals, and they were waiting for the females to enter or leave the bamboo tubes.  They may well have been out of luck though because any female nesting will already have been mated and from what we could see, none of the females were interested – entering and leaving the nests as quickly as possible.

Red Mason Bee Male. Note pale hairs on face and his passengers (mites)

Red Mason Bee Female, and you can just see her horns

The species of bee was the red mason bee (Osmia bicornis).  It is called the red mason bee because of the gingery hairs on their abdomen and because, if no bamboo tubes are available, they will dig themselves a tube by excavating holes in soft mortar.  In common with other solitary bees that nest in this sort of hole, the female will go to the far end and build a pile of pollen mixed with nectar.  She will then lay an egg on the sticky lump of pollen and seal up the hole, creating a cell in which the egg can hatch safely.  She will then build another pile of pollen and nectar in front of the cell, lay an egg, and so on, creating a series of cells along the tube until she runs out of room.  She may then go on to find another tube or she may run out of eggs or energy and die.  This means that there is no maternal contact between the adult bee and her offspring that won’t emerge until next spring, and everything that the offspring need to know about being a bee (including how and when to emerge) has to be coded in their DNA.

When the eggs hatch into larvae, they will eat the pile of pollen provided, spin a cocoon around themselves and go about the metamorphosis business, going from larva to pupa, and finally emerging from their cocoon as an adult bee.  The adult bee then stays in its cosy cell over winter, emerging when the weather warms up and there is nectar and pollen available so that they can feed themselves up ready to found the next generation.

You may have noticed the word bicornis in the scientific name, which is latin for two-horned.  This refers not to their antenna but to a couple of prongs on the female’s face which are used to tamp down the mud that they use to seal the holes.  The female doesn’t carry the pollen on her legs like other bees, but in the pale hairs underneath her abdomen. 

Ruby-tailed Wasp

Ruby-tailed wasps may also be seen near the nests which, though beautiful with their red and green metallic colours, prey on mason bees.  It was fascinating to watch the female bee carrying mud in her mandibles into the tubes and then, when the cell was sealed to come out, turn round, and back into the tube to lay her egg – several minutes, or hours well spent.