A nine-legged tick: Report of a morphological anomaly in the blacklegged tick, Ixodes scapularis (Acari: Ixodidae) from the northeastern United States

Morphological anomalies have been reported in the blacklegged tick, Ixodes scapularis (Acari: Ixodidae), from the northeastern and upper Midwestern United States, complicating identification of this important vector of human pathogens. Here, we report a case of a local morphological anomaly in I. scapularis, parasitizing a human living in Connecticut. We used a dichotomous morphological key, high-resolution and scanning electron microscopy images, as well as DNA sequencing for identification. The specimen was identified as an adult female I. scapularis with the left leg II split at the trochanter, resulting in two complete legs from the femur to pretarsus giving the appearance of five legs on the left side versus four on the right side. Here we discuss recent reports of morphological anomalies in I. scapularis, and highlight the need for further studies of teratology in this important tick species and its potential implications.