Cockroaches emerge in California heat. Why do they come in your home and can you avoid them?

As temperatures heat up in Northern California, you may begin to see more cockroaches while outside, and on occasion — inside.

Cockroaches become more active in late spring and early summer, as cold blood insects generally thrive in warm and humid weather. The warmer it is, the more active they are, UC Davis entomologist Lynn Kimsey said.

Stumbling upon the lengthy, flattened insect at home tends to incite feelings of disgust and fear. The most immediate concern upon seeing one is how to get rid of it.

The Bee talked to bug expert Kimsey for some answers on the harrowing insect, why they come indoors and what to do if you see one in your home.

Identifying a cockroach

For the most part, cockroaches are unmistakable critters. They are known for their long, protruding antennae and shield-shaped torsos, known as the pronotum, according to the University of California, Integrated Pest Management Program.

Cockroaches are generally nocturnal creatures, and if they’re spotted during the day, it is a sign of a robust population, Kimsey said.

In California, there are currently eight exotic species of cockroaches. And only the species found in the state that is a cause for concern is the American cockroach.

Because this species can carry and spread bacteria, restaurant inspectors look out for the American cockroach as sign of filth. However, most other cockroaches are clean insects.

Additionally, the hair, cuticle and debris left behind by American cockroaches can cause allergies and, in rare cases, lead to asthma, according to a Bohart Museum of Entomology.

“It is really, really unlikely you’re going to have an American cockroach in your house unless you’ve got really filthy conditions,” Kimsey said.

The other two cockroaches that raise concerns of filth are the brown-banded and German species.

The American cockroach is considered an indoor pest and measures at around 1.5 inches, representing one of the longest cockroaches in California. They can also be identified for their chestnut brown color.

However, the ones most frequently spotted in California homes are the Oriental and Turkestan cockroaches, which are fairly harmless insects, Kimsey said.

“They are both super abundant right now because it is dry and warm,” Kimsey said of the two species’ populations.

They are notably smaller than the American species and can range from 0.25 inch to 1 inch in size.

Why do they come inside?

In short, cockroaches crawl inside homes in search of water.

The roaches that come inside your home have most likely made a mistake, Kimsey said. They are unable to live indoors due to a lack of moisture.

Most cockroaches are outdoor bugs that eat decaying plant material and other debris.

“You might think of them as little garbage collectors outside when they’re neatening the forest and keeping the debris piles down,” Kimsey said.

Indoors, they tend to hide in dark, moist places and can be found behind refrigerators, in kitchen appliances and the undersides of furniture, according to UC IPM.

How to avoid them

Unfortunately, there aren’t many ways for people to prevent cockroaches from entering their homes, Kimsey said. They can flatten out and crawl into openings as small as an eighth of an inch.

She does not advise spraying your home with chemicals in order to prevent them, unless in severe situations or in the case of an infestation.

“It’s just something that’s going to happen,” Kimsey said. “You can spray your yard … but really what’s worse — one cockroach or all the insecticides you’re exposing yourself to?”

If you see one inside, it doesn’t mean your home is gross or dirty. But you’ll probably want to get it out anyway — and you definitely don’t want an infestation. Here are some ways to prevent cockroach infestations, according to the Bohart Museum of Entomology resource guide on cockroaches:

▪ Remove all sources of food from kitchens and countertops. Never leave food out overnight.

▪ Store food in plastic, glass or metal containers with tight lids.

▪ Keep kitchens, storage areas clean.

▪ Keep yards and garages clean.

▪ Consider not feeding your pets outside.

Otherwise, Kinsey recommends people use their shoes to squish a cockroach and dispose of them outside or in the garbage.

Products that contain boric acid, which are effective against cockroaches, are another way to manage a cockroach infestation. They come in a variety of forms, including liquid, gel, capsules and powders.

However, if you spot an American cockroach in your home, it is advisable to call pest control.

“There are a variety of things you can do,” Kimsey said, “but if you do have American cockroaches [in your home], then you have a larger issue than the cockroaches.”

This story was originally published June 3, 2022 at 5:00 AM.