Williston residents may be noticing some unwanted visitors late this season.
The mosquito population has risen so quickly recently that the city plans to spray tonight.
The vector control department has been tracking the mosquitoes using its trap line, which ranges from Trenton through Carolville.
Vector control has certain criteria that needs to be met for mosquito population.
If any given trap gathers 10 or more of a specific types of mosquito, this triggers a spray of the area.
Up until recently, the mosquito population had been holding steady, but since this weekend three traps were triggered four times.
This prompted the city to make an unexpected September spray tonight.
(Francis Bosch, Vector Control Director, Williams County) "Numbers overall are not so bad but it is just the fact that these are vector mosquito's. I am surprised myself that we would be spraying this late in the season. It's nothing we haven't done before but it's something we would like to think we are through with this."
As of last week, North Dakota Health Department has had no cases of West Nile Virus among humans but Bosch says he is concerned due to the increase of mosquitoes.