Enlargement of sternite 5/6 in females of many Conopidae, sternite 5 is then produced ventrally as a pad-like structure anteriorly and with a variously developed plate-like portion posteriorly; sternite 6 often similarly developed but with pad-like anterior portion usually smaller and with pate-like posterior portion usually larger than those in segment 5.
Illustration showing a female of Conops flavipes, but in, for example, Sicus the theca is much smaller and rather inconspicuous.