Wednesday, 11 March 2015

SO much more than a hole in the ground!

This tiny little hole (around 3mm in diameter) is the entrance to a solitary mining bee's nest. Each individual female solitary bee chooses an area of compacted sandy soil and digs her own tunnel. Some ground nesting bees choose south facing slopes, whilst others prefer to construct their nests amongst the roots of trees, or in river banks.  

After she has dug the main tunnel, the bee constructs a number of offshoot tunnels and at the end of each of these she fashions a small chamber. Each chamber is first waterproofed using an anti fungal secretion from the bee's Dufour's gland, then provisioned with pollen, which the bee has collected over many trips back and forth to the nest. Although most bees are not too fussy about where they source their nectar, they can be slightly more fussy when it comes to choosing pollen to provision their nest. Andrena clarkella, for instance (one of our earliest emerging ground nesting bees) relies heavily upon the pollen from Willow (Salix spp.) So, it is of paramount importance that the right plants are in flower during the nest provisioning period.

Once she has provisioned the chamber with sufficient pollen and a little nectar, the female solitary bee lays a single egg in each chamber. When this process is complete, she fills in the entrance to the tunnel and may then go on to construct a few more nests before she dies. She is on the wing (above ground) for approximately 4 - 8 weeks. 

When the eggs hatch, the larvae will feed on the pollen before pupating. After they have pupated they remain beneath the ground till the following spring, when they emerge as adult bees, mate, and start the cycle all over again.

So, next time you see a little hole in the ground like this…..make time to stop and watch for a while. You will be enthralled and enchanted by what you see!

Here (below) are two of the more common solitary bee species you might see making their nests in these tunnels. The orange coloured bee is a Tawny mining bee (Andrena fulva)  and the black and grey bee is an Ashy mining bee (Andrena cineraria).

You may also notice small yellow and black striped bees (like the one in the photo at the bottom) buzzing around the holes. These are Nomada species (cuckoo bees) who nip in and lay their own eggs in the nests of the solitary mining bee. When the nomada eggs hatch into larvae, they eat the pollen that has been carefully provided for the mining bee larvae. Very cheeky! 









N.B. some of these nests belong to solitary wasps. Neither the solitary wasps, nor the solitary bees are likely to sting you.

For more information about ground nesting solitary bees and the importance of short grass and bare soil for habitat, do please watch this little video of an interview I did with Stuart Roberts, chairman of BWARS (Bees , Wasps & Ants Recording Society)  

Importance of short grass for ground nesting solitary bees

6 comments:

  1. My Forest School groups discovered some of these little holes in our wood last year. After first speculating that they may be mini molehills I encouraged them to research the architects of these little mounds further. They were fascinated to find out they they were in fact the work of solitary bees

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  2. My Forest School groups discovered some of these little holes in our wood last year. After first speculating that they may be mini molehills I encouraged them to research the architects of these little mounds further. They were fascinated to find out they they were in fact the work of solitary bees

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  3. I found this site after trying to identify these holes I keep finding out on a walk. Thank you for putting me out of my misery! I had an idea they were some kind of burrowing insect, thrilled to find out they are bees.

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    1. Make sure to spend some time watching the holes....you will be delighted by the resident bees and their behaviour!

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