Those are likely eastern tent caterpillars or forest tent caterpillars.  I suspect eastern tent caterpillars.  Both species are among the earliest active insects in the spring and will form webbing starting in the crotches of branches on host trees.  They extend the webbing as they consume early emerging foliage.  Their feeding rarely causes significant harm to the tree and only give it an unsightly appearance.  This insect has been feeding on foliage in the tree probably since mid-March.  Most of the caterpillars should have dispersed from the webbing by now because they are looking for places (called wandering) to pupate (make their cocoon).  Adults emerge sometime in July and after mating lay eggs on small diameter stems of Prunus or crabapples.  They do not causes significant harm to a tree and no treatments are warranted.  If control is desired, you can tear open the webbing with a stick and then birds and wasps will eat the caterpillars.  The webbing is formed by the caterpillars, not spiders.