thyridium (noun; plural
thyridia; Greek diminutive
thyris, window): (
Arthropoda:
Insecta) 1. A small whitish spot in the wings of Neuroptera, Hymenoptera and Trichoptera. 2. In ichneumonid Hymenoptera, a scar-like
area on each
side of the second abdominal
tergite, between the middle and
base; the third
tergite rarely may have tyridia.