During summer, we might see some uninvited visitors in the house: ants, cockroaches, mosquitos (small flies).
As I don't like to use chemicals. my favorite 'killer' is water. Yes, water kills. I spray the ants with plain water, and instantly get rid of them.
With the cockroach it takes a bit more time. Water seems to disable it from running across the floor, but it can still crawl. After a day or two, I'll find it tough, inactive or even dead. Cockroaches are said to carry disease, so the water method is good but not good enough. I should find a way to dispose of them faster.
Mosquitos are also considered disease carriers. I can handle the bite - usually by applying vinegar on it. I could prevent the bites with clothing covering arms and legs. In my experience, the best mosquito repellent is a fan. I've got a small fan on my desk, and when ON, it definitely keeps mosquitos away.
There are many species of these 'visitors' in Nature. Luckily, mine are of an 'inferior quality' with regards to breeding and damage. It's possible to have zero such visitors, but I live in an old building, with the kitchen facing south, and other enviromental issues.
Anyhow, no need to waste time, and money on chemicals. The natural things we have at home can help provide adequate solutions (garlic powder, baking soda powder, mint, lavender, citronella candles, fans, etc..).