Verbena is a beautiful but lucious flowering annual and slugs, snails, earwigs and caterpillar- like worms love to eat the leaves and flowers.  If you do not see slime from slugs or snails then look just under the soil near the base of the plant for a larvae or worm. You should also check under the foliage for hiding insects and destroy them. You can snip off the damaged flowers and new buds and blooms will form for color all summer if you protect the plant from pests. Verbena likes full sun and good drainage and you can fertilize with Osmocote plant food at planting time and the nutrients will be released slowly all summer. Keep growing, Marianne Binetti