Why do roaches come

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Last updated: April 8, 2026

Quick Answer: Cockroaches primarily come indoors seeking food, water, and shelter, with German cockroaches being the most common indoor species worldwide. They can enter through cracks as small as 1/16 inch (1.6 mm) and are attracted by food residues, moisture, and clutter. A single German cockroach can produce up to 400 offspring annually, leading to rapid infestations. They are most active at night and can survive for weeks without food but only about a week without water.

Key Facts

German cockroaches (Blattella germanica) are the most prevalent indoor species globally, accounting for over 90% of infestations in some regions
Cockroaches can enter buildings through openings as small as 1/16 inch (1.6 mm) in diameter
A single female German cockroach can produce 4-8 egg cases (oothecae) in her lifetime, each containing 30-40 eggs, potentially yielding 400 offspring
Cockroaches can survive for up to 1 month without food but only about 1 week without water
Cockroaches are primarily nocturnal, with peak activity occurring between 2-4 AM

Overview

Cockroaches are ancient insects belonging to the order Blattodea, with fossil evidence dating back over 320 million years to the Carboniferous period. Of approximately 4,600 known species worldwide, only about 30 are considered pests that associate with human habitats. The German cockroach (Blattella germanica) first appeared in Europe around 1767 and has since become the most common indoor cockroach globally. American cockroaches (Periplaneta americana) likely originated in Africa and arrived in North America via ships in the 1600s. These insects have evolved remarkable survival adaptations, including flattened bodies that allow them to squeeze through tiny openings and rapid reproductive capabilities. Their association with human environments has made them significant public health concerns, particularly in urban areas where they thrive in warm, humid conditions near food sources.

How It Works

Cockroaches enter buildings primarily through three mechanisms: active migration, passive transportation, and structural vulnerabilities. Active migration occurs when cockroaches walk from neighboring infested areas through shared plumbing, electrical conduits, or wall voids. Passive transportation happens when people inadvertently bring cockroaches inside via grocery bags, cardboard boxes, used appliances, or furniture. Structural vulnerabilities include cracks in foundations (as small as 1/16 inch), gaps around pipes and cables, and poorly sealed doors and windows. Once inside, cockroaches follow scent trails (pheromones) left by other roaches to locate food, water, and harborage sites. They are attracted to carbohydrates, proteins, and fats, with particular preference for starchy and sugary substances. Moisture sources like leaky pipes, condensation, and pet water bowls provide essential hydration. Cluttered areas offer ideal hiding places, with German cockroaches preferring warm (70-75°F), humid locations near kitchens and bathrooms.

Why It Matters

Cockroach infestations have significant public health implications, as these insects can transmit at least 33 kinds of bacteria, 6 parasitic worms, and 7 human pathogens. They are particularly problematic for asthma sufferers, with cockroach allergens present in 60-80% of urban homes contributing to increased asthma symptoms and hospitalizations. Economically, cockroach control costs U.S. households and businesses over $1.5 billion annually in pest management services and product purchases. In food service establishments, cockroach sightings can lead to health code violations, temporary closures, and reputational damage. Beyond health concerns, cockroaches cause property damage by contaminating food supplies, staining surfaces with their feces, and producing unpleasant odors from aggregation pheromones. Their presence often indicates underlying sanitation or maintenance issues that require attention.