Adult newts eat small invertebrates such as worms, snails, slugs, sowbugs, and insects. They also consume amphibian eggs and larvae, including newt larvae and newt eggs. Larvae typically eat small aquatic invertebrates and decomposing organic matter.
In the Santa Monica Mountains and Simi Hills, mating and egg-laying generally occur from November until July. Adults migrate from terrestrial habitats to ponds, reservoirs, and pools in streams to breed, typically beginning anywhere from late December to February, depending on rainfall amounts. Females lay and attach a spherical egg mass to submerged vegetation, branches, or under rocks in quiet stream pools. Egg masses contain from 7-47 eggs. Females can lay up to 3-6 egg masses in a single day. Eggs hatch at 14-52 days.
The larval stage lasts several months. Larvae transform and begin to live on land at the end of the summer or in early fall. Metamorphosis takes about 2 weeks, as the tail fin is absorbed and the gills are reduced. Transformed juveniles leave the water with adult coloration and characteristics and with a trace of gills remaining. Juveniles leave the natal pond and travel overland where it is assumed they take refuge and do not return to the water until they breed.
Southern California newt populations have suffered population declines due to habitat loss and alteration caused by human activity, and from introduced predatory fish, crayfish, and bullfrogs, which eat the larvae and eggs. Breeding ponds have been destroyed for development, and stream pools used for breeding have been destroyed by sedimentation caused by wildfires and agricultural practices. California newts are currently listed as a California Species of Special Concern (California Department of Fish and Wildlife) and are a park species of special concern. The California newt is one of the target species in the park's aquatic amphibian monitoring program.