I accidentally broke a tip branch of apple with some flower buds and blossoms and brought it inside to enjoy on the kitchen table. A few days later we found a 1/2" and a 1/4" caterpillars munching away on the leaves and petals. The 1/4" one obviously had hatched recently. Green with black heads ID'd as leaf roller caterpillars. Young caterpillars, whether they make tents or not, typically use "silk threads" as tether lines. Caterpillar poop are the color of whatever they eat and may account for the red liquid.
Could this be what you have?
I'm inspecting my apple tree every day to see if there are signs of significant damage. I'll spray with Bt if there is. I'm hoping all the wasps and Robins I'm seeing around the tree are taking care of the caterpillar problem.
Once the petals fall -- falling now -- and the rains forecast since yesterday and thru Monday is over, I'm going to spray with Surround.