If you are traveling in 2018, be aware of where you stay, because you may end up bringing unwelcomed visitors with you when you return home. That’s because bed bugs are flourishing in many large cities and not leaving anytime soon.

“Bed bugs are notoriously difficult to eradicate,” said Paul Curtis, director of technical services at Terminix, the pest control company. “They can travel to new locations very easily—hitching a ride on clothing, handbags, suitcases and taxis, which can create substantial infestations in no time.”

Terminix has seen bed bug infestations increase since the late 1990s and recently compiled a list of the cities that seem to be facing the highest incidence of bed bug problems, based on the company's service requests.

While researchers are unsure of the exact causes, factors such as increased international travel and insecticide resistance are considered likely explanations for the increase.

Bed bugs can hide for months. Signs of an infestation may include reddish-brown blood spots on sheets or mattresses and a strong musty odor. Sometimes you can just see the pests crawling around. They resemble the size, shape and color of an apple seed.

Terminix compiled the list by collecting service requests from more than 300 of its branches across the country between Jan. 1, 2017, and June 30.

In descending order, these are the cities that reported the worst problems:

10. Philadelphia

About 70 percent of bed bugs hide in your bed and 30 percent in crevices in the walls, floors and any clutter you have around your bed, according to Philly.com.