tenant reports ants.spiders, does landlord pay for pest control?

[Lilly Fang]

The tenant reported that they have recently noticed an increase in bugs and spiders inside the house and wasps in the front yard. They got scared that the kids will be bitten by spiders. They would like to have a pest control service which costs $40/month, and asking whether we (the landlord) would cover that cost. They have lived there for 4 years, and this is the first time they reported this. We are in California. I checked the law says landlord is responsible for pest control to keep the house livable.But our house has no pest problem before and not sure if this is due to their own negligence or our house. How should I proceed this?