Yes, slugs have long been considered to be the major leaf-eating culprits of new plant growth during spring. (Let’s add brown garden snails to that group.) For the most part, slug/snail baits and search-and-destroy tactics help manage both these pests. Another possible pest, but far less visible, are winter cutworms (Noctua pronuba).

Winter cutworms are invasive insects that were first seen in Oregon during 2001, then identified shortly after. These caterpillars have rather unusual habits in that they feed at night during the winter, whenever night-time temperatures are 40F or above. The adult is a moth, the large yellow underwing.   

Since then, winter cutworms have been important pests of lawns, vegetables, and many ornamental plants. In may garden, they specialized on the leaves of Pacific Coast iris and hostas.

General management for caterpillars in home gardens relies on several strategies: Handpick the caterpillars; feed them to the chickens; destroy the pupae (resting stage; see Figure 5 on page 3 in the link below) found while working the soil in the spring; or use Bt (Bacillus thuringiensis). Unfortunately, Bt is effective only when the caterpillars are less than half-grown so, right now, it’s too late for that.

The “Large Yellow Underwing, A New Cutworm in Idaho” (published in 2009) contains a detailed description of these sometimes voracious caterpillars, as well several images of their activities in Idaho’s agricultural fields shortly after they arrived.  http://www.cals.uidaho.edu/edcomm/pdf/CIS/CIS1172.pdf. Please ignore the suggested pesticides as they are not for home use.