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The warmer weather and abundant food sources that come with summer can be expected to result in an increase in insect activity. While this is vital for the overall health of the ecosystem, it can result in a great deal of frustration when outdoor insects decide to find their way into your home or office. While some insects will enter a building if they find a space suitable for establishing a colony, others typically only invade in search of resources. The latter are referred to as perimeter invaders, or occasional invaders.

Perimeter invaders are insects and arthropods that typically live and breed outdoors, rather than colonizing or laying eggs inside of human dwellings. Rather than seeking a place to establish a colony, they will enter human homes in search of food, water, or other resources that are more abundant inside than they are out of doors. They may enter individually, or may turn up in large numbers, with very little warning. In addition to being an unsightly nuisance, some species classed as perimeter invaders may bite, sting, or excrete substances that cause a painful reaction in people with allergies or sensitivities. If they die inside the home, their bodies may prove an attractant to insectivorous species.

In York Region, the most commonly encountered perimeter invaders are earwigs, centipedes, and millipedes.


Earwigs range between 0.5cm and 2.5cm in length, with long, slender, flattened bodies between tan and dark brown in colour. The earwig's most distinctive feature is the large pincers extending from the bottom of its abdominal section. While these pincers are fearsome looking, earwigs are actually relatively harmless, in that they will generally not interfere with humans or companion animals, and will only pinch in self defence.

Earwigs make their homes in burrows in the soil, and lay their eggs inside these burrows come spring. They prefer damp soil, and will often lair in garden mulch, or under logs and rocks. They are primarily nocturnal, and will rarely be seen during the day unless their nests are disturbed. In the home, they will generally be found in cool, damp locations, such as near kitchen or bathroom sinks, though they can be found foraging in other areas of the house. They eat insects and decaying organic matter, and will usually enter the home in search of food. Regular sightings of earwigs inside the home may indicate a problem with moisture in the area they're frequenting.


Centipedes are long, slender, light brown arthropods, varying in length from 0.5cm to an impressive 5cm. Their most distinctive feature is their numerous spotted legs; the number ranges from 15 pairs to nearly 200 pairs, with one pair per body segment. Most centipedes are carnivorous, and utilize venom to paralyse their prey for ease of consumption. Their bites can be extremely painful, but they do not produce enough venom to be lethal to a human being. Like all venomous species, however, they may provoke an allergic reaction in those susceptible.

Centipedes prefer damp, dark, quiet habitats, and will commonly be found beneath piles of leaves, grass, compost, or bark. They lay their eggs in the soil in the summer. They are nocturnal, and will rarely be spotted during the day. Indoors, they may be found in damp locations, particularly around the bathroom and basement. Frequent centipede sightings may indicate an unusual degree of moisture buildup in the areas they're frequenting. Typically, centipedes will enter the home in search of prey. Infestations by soft-bodied insect species may attract them, as they will provide a steady source of food.


Millipedes are dark brown or black in colour, with long, thin bodies ranging between 0.5cm and 3cm in length. Like centipedes, they have numerous legs, though they possess two pairs per body segment to the centipede's one pair per segment. Their legs are also less visible from the side or top than a centipede's longer leg. While their name means "thousand feet", they actually have between 11 and 375 pairs of legs. Though millipedes do not have any active defensive structures, such as stiners, pincers, or mouths equipped for biting, they do secrete a foul-smelling substance that functions as an irritant and may cause an allergic reaction in sensitive individuals. This substance will burn if introduced to the eyes, so it is advisable to be sure to wash your hands before touching your face if you have been handling a millipede.

Millipedes live outdoors, and lay their eggs in the soil. They're typically found in damp locations, such as flowerbeds, beneath leaf litter or piles of grass clippings, or under damp wood. They feed on decaying organic matter, such as dead leaves and decaying wood. Inside the home, they're typically found in cool, damp locations, such as basements and crawl spaces. They will occasionally enter the home after heavy rainfall, or in search of food.


There are several steps you can take to reduce the likelihood of perimeter invaders disturbing your home. Make sure to check the caulking around your windows and doors, re-caulk as needed, and keep your screens and weather stripping in good repair. Seal any cracks in your walls and the foundation of your building, as pests may enter through even minute cracks.

In addition to minimizing entry points for perimeter invaders, you can make the area directly surrounding your house inhospitable to them. As the most common species of perimeter invaders in York Region prefer damp soil and organic litter, you should keep the area directly around your house free of debris. Clean up fallen leaves and cut grass promptly, and avoid leaving compost piles within several feet of your building walls. Keep any firewood off the ground, and do not store it directly against your house. Keep your eaves troughs and exterior drains clear of debris, and ensure they drain away from your home, not toward the foundation. Keep an eye on any areas of your home prone to dampness, and repair leaky pipes or faucets promptly, as denying any pests that do make it into your home a comfortable environment will diminish the likelihood of them staying.

If you have a persistent problem with perimeter invaders, outdoor chemical treatment may help to deter them. If you feel the need to make use of chemical treatments, you're advised to contact a pest control professional. They can analyze the situation, and determine a solution that will best meet your specific pest control needs.