I have a large balcony in London with lots of plants in containers and troughs. There are always a lot of spiders webs strung between plants. This morning I noticed lots of tiny mite sized creature spreading up a web from the base on a Margarita plant.When I looked in close I saw they were tiny spiders, bright yellow with a bit of black. They were coming from a tightly packed ball of themselves at the base. I must have shaken the web because when I checked later they were tightly packed again, but any disturbance sent another lot up into the web. There are hundreds maybe thousands of them. They are too small for me to photograph. Can anyone tell me what they are. I could not see an adult spider on the web..