Hello fellow gardeners! If somebody can help me with figuring out what pest is depicted on the picture from my garden. I thought it was some kind of insect droppings but when I brought one weed inside to take a picture all those things started moving!

I about had a heart attack! First, they were on the fence then on some weeds near the fence, now on the new blackberry plants near the fence. Please help me to find out what those nasty things are and how to get rid of them! Thank you in advance!!!!