In pest-speak, occasional invader refers to insects and critters that normally belong outside but somehow wander into your building. Examples include millipedes, boxelder bugs, earwigs, and black vine weevils.
This time of year, they are growing in population. Chances are higher that their population will overflow into your building. Be vigilant in scanning your buildings for these occasional invaders.
They don’t survive well in clean indoor environments and will probably not grow into infestation levels, but we do want to protect our guests from seeing creepy crawlies!