It’s debatable, but most will say either termites or bed bugs are the hardest to remove. When dealing with termites, you must find the central nest (as opposed to satellite nests) and exterminate the queen and all potential queens, which often takes the work of a specialist. Bed bugs, meanwhile, are incredibly hardy, good at hiding, and resistant to pesticides, so it takes very careful, very thorough work to get rid of them permanently. 

Spraying for ticks does a good job of eliminating the existing ticks in your yard. Moderate to severe infestations might require several treatment sessions, but most infestations are well controlled with enough treatments, regardless of their severity.

However, wildlife, pets, and people can still carry ticks into a yard, even after treatment, so if you're concerned about ticks in your area, it's a good idea to spray annually for tick prevention.

On average, fleas can leave for about 2 to 3 months in your carpet. However, if they have access to a host for feeding, they can return to the cozy carpet and live much longer. That’s why it’s essential to remove fleas from your carpet quickly before they take up permanent residence.

The hardest ant to get rid of is the pharaoh ant. Although small, pharaoh ants can spread infections in hospitals and are known to transmit infectious diseases in schools, apartment complexes, and office buildings. For this reason, they’re best handled by pest control professionals.