Red spider mites are the most likely perpetrators. They like arid settings and are most active from March to October.
Remove the contaminated plant right away. Make sure to look for cross-contamination in all of your other pitcher plants. After taking the plant out of the pot, thoroughly clean the roots by washing off the dirt.
Plants should be repotted in new soil and kept under quarantine until new growth emerges and the plant becomes established again. To prevent new infestations, make sure the soil is moist. When you are certain you have solved the issue, put the pitcher plant back where it was.