I contacted Norfolk Wildlife Trust with details including bee video footage to see if they could shed some light on this. Below is an extract from their reply. Please can people be more mindful of what they apply to their fields and gardens:
..... I can't say with 100% certainty what led to the bees dying, but in my experience, my educated guess would be poisoning from pesticide spray near to your property. I'm basing this on two main points - one being the fact that there was a large number all dying at the same time, and secondly your description of their mouth parts and abdomens - when bees have been covered in spray they try desperately to clean it off, and when they die in this way they are often found with the tongues extended right out and sometimes their sting also. I've witnessed a similar event in a churchyard a few years ago, numerous bees dying all together whilst the field next door was being sprayed. It's terribly sad, and incredibly frustrating since there is really nothing we can do - no law is being broken unfortunately. We are slowly helping to encourage farmers to be more mindful of wildlife (encouraging unsprayed field margins or reducing pesticide use for example), but it is a very slow process and certainly not widely adopted yet.
Thanks Karen for highlighting this problem with bees. They are so beneficial and a great joy to see them going from flower to flower. Do you think an organic spray is acceptable if a spray needs to be used at all?
There are some organic sprays that claim they are bee-friendly that you can buy, and there are some online recipes for making your own organic pesticide. Other than that, I can't really answer your question as I haven't used any spray in years.