These flat, yellow Yarrow flowers, are attractive to insects; that is their purpose.
However, an eight-eyed, eight-legged sprinting predator, lies in wait -- Misumena vatia, one of the Crab spiders.
It spins no web, just lies in wait and pounces on unsuspecting insects such as flies and butterflies, biting them in the neck to paralyse them with its venom.
source: Insects of Britain and Western Europe by Michael Chinery.
Both rows of four simple eyes can be seen above. See also the spiny legs with which it secures its prey.
Gardens are fascinating in detail, the more so where no chemicals or sprays are used.