The mature larvae of Zaitzevia elongata have a body length of approximately 4 millimeters (mm) long and are black or dark brown with orange appendages.

The spiracles, which are openings that allow air to enter the trachea, are found on the mesothorax and the first eight abdominal segments.

Their dorsal and ventral (top and bottom) surfaces are not smooth, and have flat granules (bumps) and various setae (bristles).

[1]: 218 The thorax of the larvae are not serrated on the sides, and the dorsum has similar granules and setae to the rest of the body.

[1]: 219 The male genitalia of Zaitzevia elongata is about 2.2 times as long as the median lobe, and the parameres are membraneous.