Solitary Bees

As the between-the-bricks bees emerged on Saturday the 12th of March as temperatures tipped 14°C, I was reminded of what I have to be thankful for having these wonderful little creatures in my environment. Explaining for the umpteenth time that they don’t make honey, nor sting, I thought it was time I shared exactly what impact these bees have.

The results are becoming clear that the more mason bee habitats – tubes, straws, reeds and drill blocks – that I put out, the more bees I get, and the more dense are the fruits are on each of the healthy 7 trees in my little orchard. Another year like the last and I will be certain that they are having a definitive impact on the pollination of the blossoms (40 metres away from their nest sites).

Speed and/or efficacy – the differences between Mason Bees and Honey Bees :

In several different places I read that mason bees are ten times more effective pollinators than honey bees, ‘facts’ I have gleaned are:

• A study recorded that honey bees visit 5% of the blossoms on a tree and that mason bees visited on average 97% (will have to find that source);
• Honey bees can forage up to 3km from their hive whereas solitary bees are more local foraging in a 300m radius – which may make their round trips more frequent;
• Honey bees put the gathered pollen mixed with nectar in sacs on their legs – solitary bees ingest the nectar and mostly put pollen on their forked abdomen hairs (Scopa) – which may mean more pure, loose pollen is falling off and being dusted around by mason bees;
• They have a considerable work rate – given the right conditions (mainly adequate clean tunnels) certain bees can expand their populations by a factor of six. I have so far seen a quadrupling of my population in 2009 and similar cell creation efforts in 2010.
• [update 24/08/2011] - mason bees actually fly faster than honey bees according to this US video on native pollinators.
• [update 30/03/2012] - mason bees stock just enough pollen and nectar for the single new progeny, their work is directly related to new bees. 
  

This is all great however the main thing that convinces me that they are more effective pollinators is their behaviour observed during their nesting activities.

Behaviour of female mason bees.

They are programmed to behave as if there is a limited supply of tunnels (which is now often the case with human-controlled and landscaped habits).  Why they are frenetic, even anxious is more and more evident when you sit and observe their activities:

1. There are limited nesting sites:  Being non-excavators of tunnels (they rely on insect bore holes in wood, or other insect spaces in walls) so nesting space is scarce and nature has selected the qualities that make them maximally exploit these limited tunnels.
2. Losses by parasites and predators: There is also the issue of parasites stealing their work or killing their larvae, or tunnels being blocked over the 11 months from larvae to emergence phase, so just maintain their gene line, they have to make as many cells as possible (just like turtles lay a thousand egg to achieve a handful of adult individuals).  I have heard that a female mason bee may create 30 to 35 nest cells.
3. Being solitary means that they can’t defend their work and stop other bees from stealing it whilst away collecting pollen, so they have to do this as fast as possible and the females deal roughly with the interlopers discovered in their tunnels. I frequently see and record females fighting in the plastic tubes I set out. They will chew the hair off an interloper’s back if it is inside the tunnel before them – at the end of April nesting season I often see exhausted bees with what I’d call  ‘reverse mohicans’, sort of black dorsal stripes on those that have been nesting and competing for a while.
4. Frequently in front of the tunnel entrances they’ll attack in mid-air any females that they believe are going to the same entrance.
5. They live only four to six weeks so time is ticking,
6. Occasionally I find them literally dead or exhausted in front of the tunnel entrances.
7. They are ‘aware’ of their mortality – what I mean by this is that I very rarely find a tunnel containing nest cells that has not been double blocked.  It is as if they know they have to finish the work to protect their progeny and thus make a judgement call as to how much energy they have left and whether it is enough to create another last cell and double block it (3cm from the entrance + extra thick at the entrance).

I have thus come to refer to my female mason bee (Osmia cornuta) behaviour as ‘anxious’ – I am not sure if this is also the case with other Osmies.

Of course this is all anecdotal evidence, but I think the anxiety analogy/pseudo-hypothesis has its merits. I am starting to see more and more and evidence of how they are great for the organic fruit production in my garden – last year having 400 bees emerging from cocoons, I could say I had the equivalent of 4000 very anxious and frenetic short range honey bees helping my garden grow.

This entry was posted on Thursday, March 31st, 2011 at 3:24 pm and is filed under Fruits of their labour, good day, learning curve, results, solitary bee females. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.