Butterfly Orchid Hybrids in Gloucestershire

I have been intrigued by the hybrid between Lesser and Greater butterfly orchids for 2 or 3 years now.  It is not common, not least because there are few places where the two parents grow together.  Our croft on Skye had both and there were a few hybrids, around 2 to 3 per year out of a total population of over 100.

Near Cranham and south towards Slad in Gloucestershire there seems to be a hotspot.   I have seen  are at Sheepscombe, Bulls Cross, and on Cranham Common.   On Sunday I went to another location in that general area, Butterfly Conservation's Strawberry Bank reserve. 
     

Strawberry Bank

On the bank itself there were mainly Lesser butterfly, while at the bottom near the woodland edge were a few Greater.  There were though amongst the Lesser a few hybrids, looking like the former but with the pollinia not parallel, yet not as wide as for Greater. 

Lesser

Greater

Hybrid

 I made a few measurements comparing one hybrid plant, one Greater and 7 Lesser:

	Subtended	Spur	Viscidia
	Angle deg.	Length mm	Distance mm
LBO (Av)	1.9	21.8	1.2
Hybrid	26.0	21.9	3.7
GBO	36.0	29.6	3.8

Note that the viscidia are the sticky pads at the bottom of the pollinia stem (caudicle). These are what attach the pollina to visiting insects to effect pollination.  

On this particular example the subtended angle was larger than others I found there.

Looking for hybrids I had less success when trying to find them again in 2 locations where the BSBI database has records.  At Bix, in BBOWT's Warburg reserve, Greater are scattered throughout, though never plentiful.  There are just a few Lesser, actually growing close to Greater, but there were no hybrids.  Probably not enough of both parents.

Llynclys Common in Shropshire is another site where there is a record and I called in on my way home for relief after a challenging day (and a purple haze in front of the eyes, as anyone who has been there will know) looking at the marsh orchids at Ynys Las.  Llynclys Common is a Shropshire Wildlife Trust reserve, and I found Greater among bracken and bramble, in small numbers but with no sign of Lesser or any hint of hybridisation.  

Llynclys Common where there is an old hybrid record

Greater

 So why is Cranham / Slad such a hotspot?