The warmth of March and April is definitely welcome, but does have one unpleasant side effect for those of us who do not like insects wandering about the house. The warmth and sunlight warms up insects that are hibernating in the walls of the house and these insects often accidentally crawl into the living spaces of the home.
The most common is the multicolored Asian lady beetle. They overwinter as adult beetles in the walls of homes and emerge in the spring. If all goes well and they live long enough, they will return outside to lay eggs. The have been happily spending the cold weather in the walls, but the warmer days combined with the heat of the house often warm them to the point where they can become active and wander around. Those that wander inside are doomed because there is no food (aphids or other plant pests). They are often found around sinks or in showers where they are looking for water. They are also attracted to lights at night.
Other insects that tend to wander out in the spring are boxelder bugs, cluster flies and larder beetles. Larder beetles are not really an accidental invader that is overwintering in the walls. Larder beetle adults and larvae feed on the dead insects in the walls of the house. Although you may see a lot of lady beetles and boxelder bugs alive, many more do not survive the winter and are dead in the walls of the house. Larder beetles serve as nature's recyclers and feed on these dead insects. Larder beetle adults are usually what people notice wandering about in the house.
Although this influx of insects is very disturbing to the homeowner there is very little that can be done in the spring. It is not necessary to try to spray the insects in the house as they will die quickly anyway and it is not possible to gain easy access to the interior of the wall space in order to inject insecticide. If accidental invaders have been a consistent problem over several years you can consider using insecticides on the outside of the house in the fall to reduce the number of insects that get into the wall space.