I Found an Insect in my House! What Should I do? Back »

Written collaboratively by Amanda Bachman, Patrick Wagner, and Adam Varenhorst.

Many people live by the tenet that the only good insect is a dead insect, and that insects and other arthropods should only live outdoors. Under this assumption, any arthropod or insect that crosses the threshold requires immediate control, either by swatting, squishing, or spraying with an insecticide.

In actuality, our homes host a diverse assemblage of arthropods and insects throughout the year. This activity often goes by unnoticed and the vast majority of these critters don’t cause us any harm. However, there are some arthropods and insects that we definitely don’t want as roommates. Keeping every insect out of our homes is virtually impossible, especially as our homes start to naturally age. Most of the time, the arthropod and insect invaders make their way into our home through small cracks and spaces around doors and windows. In more severe cases, they are making their way in through holes or cracks in roofs, siding, or foundations. For most individuals, the best approach is to adjust your expectations, and come to terms with the idea that there are probably insects inside your home year round. The first steps to managing those pesky indoor invaders include learning how to identify them and how to dispose of them.

The best approach for arthropod and insect invaders is to take a precautionary approach. This includes:

  • Visually inspecting the home for any structural entry points and fixing any that are found.
  • Checking the weather-stripping around doors and replacing any that doesn’t provide a tight seal or that appears to be hard/weathered.
  • Checking around windows to ensure that there aren’t any gaps or spaces around them and that they close properly without any gaps.
  • Don’t store grain or grain based products (including dry pet food) in open containers or containers that don’t provide an airtight seal.
  • Summer/fall insecticide perimeter sprays around the outside of the home.

Indoor Insect Pests

This category includes things that cause harm to humans and/or pets either by direct feeding or by infesting food or clothing items. Those that directly feed on humans or pets include bed bugs, fleas, and lice. Although mosquitos and ticks will feed on humans indoors, they are not capable of completing their lifecycle in the home. Cockroaches, flour beetles, Indian meal moths, larder beetles, carpet beetles, and clothes moths will feed on food items or animal-based household products (e.g., clothes, carpet, and, yes, even insect collections). Some of the less serious indoor insect pests can be handled either by removing the food source and storing products differently (i.e., cockroaches, Indian meal moth, flour beetles) or by using cedar (i.e., clothes moth) and vacuuming (i.e., larder and carpet beetle). However, the more serious pests such as bed bugs typically require the help of a pest control professional.

Homes with house plants may experience outbreaks of fungus gnats and other flies that spend part of their life in potting soil; however, they don’t have any adverse health effects. The best way to prevent pests of household plants is to practice good plant hygiene – don’t overwater, and allow the soil to dry out between watering.

Fall Invaders

During the fall, insects that overwinter as adults begin looking for shelter. These are the critters most commonly finding their way inside, and generate questions about their identity and motives. As mentioned, the best course of action for preventing further fall invaders is to determine their point of entry and fix it. In most cases, an insecticide is not necessary and the insects can be managed with a vacuum or a broom. However, if the accidental invader is the multicolored Asian lady beetle (Figure 1), it should be knocked into a container with a lid that can be discarded. This particular species of lady beetle is capable of emitting a strong, displeasing odor that will linger in vacuums.

Common fall invaders in South Dakota include picture wing/attic flies (Figure 2), boxelder bugs (Figure 3), multicolored Asian lady beetles, and Western conifer seed bugs (Figure 4).

Red and black spotted beetle with a white and black head area.
Figure 1. Multicolored Asian lady beetle. Photo courtesy Adam Varenhorst.

Accidental Invaders

Like their group name implies, these are the insects and other arthropods that accidentally find their way inside and even they don’t want to be there. Accidental invaders do not feed or reproduce inside, and generally can be dealt with via mechanical means (shoe, broom, vacuum, catch and release).

Every fall, we get reports of millipedes on the move that wind up in garages and basements – both places that end up being too dry for these moisture-loving arthropods. They can’t find their way out before drying out and dying. This is why they are normally observed curled up along a wall (best removed with a broom and dust pan).

Large spiders also fall into this category. It seems that the larger the spider, the more dangerous people think it is. Thus, wolf spiders (Figure 5), grass spiders, and some of the bigger orb weavers get killed only because they look scary. However, these insects do not pose a direct threat to humans and can be removed from a house using a catch and release tactic or simply by squishing them. The presence of spiders around a home can indicate an increased amount of prey present around the home. One simple method of reducing spider populations is to ensure that insects aren’t attracted to your home at night by reducing the amount of light shining through windows or reducing the time that outdoor lights are on.

Fly with brown spots on clear wings.
Figure 2. Picture winged fly. Courtesy: Amanda Bachmann

Bug with red eyes and black and red markings on its body.
Figure 3. Boxelder bug. Courtesy: Amanda Bachmann

Tan and brown bug with patterned abdomen and legs.
Figure 4. Western conifer seed bug. Courtesy: Patrick Wagner.

Large brown spider pictured in a jar lid.
Figure 5. Wolf spider. Courtesy: Amanda Bachmann

If you have an insect indoors and would like help identifying it, please submit a clear picture to the Plant Diagnostic Clinic or contact Amanda Bachmann.

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