Counting female solitary bees – 25 April 09
Have got back to the house in the countryside and have been wanting to know how things are going. Counting the number of straws/tubes/stems that are sealed is not a very reliable way, of assessing the achievements in expansion of my population.
It was something that struck me after counting the actual cocoons in the sealed straws. They varied from six to zero, plus the arrival of the small fly-like parasite Cacoxenus indagator on the paper straws reduced the number of larvae becoming cocoons. It also became a case of not counting my cocoons before they hatched – based on both the 30% losses early last year and this years observations that not all the apparent cocoons would emerge from the box (due to mould/opacity in the tubes/pollen dust obscuring the cell). So what to do? …to be really sure that my solitary expansion project is really working? The idea I came up with this week was to take a snapshot of how many tunnels were being worked at a point in time.
My reasoning: I had noted that I had in the first two weeks about five or six female bees that had emerged and were working between the bricks. They had stopped and sealed their activities three weekends ago. At the same time I had the emergences of those in the paper-straws that I had added at the end of last year when the plastic tube box was filled (34 cocooons counted in October ’08). Three weekends ago their work had amounted to 15 sealed straws. at the same time my box was in the sun and these were emerging. Last weekend there were 18 paper straws, 11 hollow stems and 15 plastic box tubes sealed. However none of these figures – however good – really reassured me that the population was expanding.
Today I arrive in the countryside and this time I decide to get a red marker pen and wait for 15 minutes and mark every tube entrance (at the top) where there’s a female working. The figure are as follows:
- Home-made paper straws – 38 sealed & 10 females active
- Hollow stems (courtyard) – 15 sealed & 5 females active
- Hollow stems (barn) – 3 sealed females active unknown
- Box plastic tubes – 28 of 44 sealed & three active females
- Total sealed = 85 & 18 females working.
As I write, totalling up these figures makes me feel rather satisfied. Considering that the project to create more solitary bee habitats started with the box construction in 2005 that resulted in c.30 sealed tubes. They emerged in 2006 creating 44/44 (89 cocoons) for 2007. Those efforts produced 44/44 sealed + 34 cocoons in the paper straws in 2008 to become the adult bees this year. It seems that we are in peak activity with the temperature around 19°C, and having 18 females working in the artificial habitats (with already 85 tubes sealed) seems to me a good result!
Here’s a video that I took of today’s progress:
So I am going to create another box or two and a drilled wooden block to provide more housing. There are some other notable things that I observe (new species, both Osmia rufu and cornuta in my habitats), but I will return later for another post.