Cockroaches are one of the hardiest and most common household invaders. Slightly larger than an inch, these creatures are fairly large and menacing in the insect world. These warriors can survive on limited resources and often times can go without food and water for about a month. They can adapt to a variety of different environments, and that is what makes them extremely difficult to eliminate. Mainly nocturnal, these pests will live on human and/or pet food and shy away once a light is turned on. Cockroaches have been linked to health issues and allergies such as asthma.