its unlikely to be the heathers. do you have water butts/ small pond or standing water nearby? It sounds like they could be mosquitoes.
We have this problem down by the workshop but as I don't go there often and hubby doesn't seem to mind the bites.

I meant to say welcome to GoY but I had to rush out and just pressed send. ;o)

I bet you are type O like I am. People with type O blood are sought out by all kinds of nasties. Amazingly, mosquitoes can detect your blood type and they favor type O blood. Unfortunately there is nothing you can do about it. Just wear long sleeves and avoid that area in the evening when they are most active. The sparrows will take care of them eventually. I hate those topical bug sprays, but citronella is a natural bug repellent. You can find it at the hardware store or home store.