Invisible insects in the currant bushes

I have several currant and gooseberry bushes, lined up in my garden for approximately 50 feet. When berries start to ripe and I am working on these bushes I experience very bad bites in the hidden parts of my body. This happens only around these bushes. I cannot see any visible insects neither on my skin, nor on the bushes. It is going on for couple of seasons now.
Does anybody know about this particular berry bushes problem? I shall appreciate response.