labium

1.A tonguelike structure in the labium of an insect.

我忽然感到有一只虫子顺着我腿往爬。

2.The mandibles are usually lost, the labrum is reduced to a narrow transverse sclerite, and the labium is a small flap ( though its palps retain quite large).

颚消，退化为一条窄横片，下退化为一小片（下须发达）。