There's a number of explanations, but there is good evidence to show that the deaths are being caused by a class of pesticides called neonicotinoids. Neonicotinoids work by disrupting neural pathways in an insect's central neural system - which in bees is extremely complex. Working in a very large group as opposed to as an individual, bees rely on their complex interactions and communications (such as the "Waggle Dance") to be able to survive as a colony. Low-level contamination by neonicotinoids doesn't necessarily kill an individual bee, but by reducing each worker bee's ability to communicate the hive loses its coherence and ability to function.
The Soil Association has a list of household chemicals which contain these deadly chemicals and should be avoided. It's not just farmers who are using these pesticides - they're available at your local garden centre!
The Soil Association is also asking you to take a few minutes to contact your MP to ask for the suspension of sale of neonicotinoids, and to press for more research into bee colony deaths. To find out more about this campaign, click here.
Please do write a letter, or an email. Help save our bees!