I just saw a ball of tiny yellow spiders with black dots clustered on the end of a Santolina stem. Are they beneficial in the garden, or should I remove them?
Your description sounds like the cross orbweaver (also called cross spider, because of the white markings on the back of its abdomen), Araneus diadematus. Its baby spiders (spiderlings) are yellow with black markings, and they crowd together and seem to move as one if disturbed. They hatch (in groups of hundreds to almost a thousand) from a fluffy-looking pale yellow egg sac. The Washington NatureMapping website has a factsheet about this species.
These industrious spiders build a new web each day (after eating the previous day’s web). They are often found close to houses and illumination (at my house, the nests appear behind the porch light) and in gardens. Their diet consists of invertebrates, so in that sense, they do provide some benefit in the garden.
Cross orbweavers in your garden are not a problem, though humans occasionally encroach on their space, and the spiders may bite in reaction to the disturbance. Some people are more sensitive to the bites than others. My strong recommendation is to let them be, and enjoy observing them.