Tanytarsus gregarius

Author: Kieffer, 1909

Exuviae 4.1-5.8mm long (m=4.9mm, n=45) (143-1.jpg).
Cephalothorax: Cephalic tubercles weak, broad conical. Frontal setae 80-115µm long (m=98.3µm, n=15). Antennal sheaths with a conical projection at base. Thoracic horn 500-998µm long (n=28) (143b.jpg); ThR 20-35.6 (n=18). The posterior thoracic mound bulbous. Wing sheaths rounded apically, pearl row absent.
Abdomen: Length hook row II 0.24-0.36x width tergite (m=0.3, n=6); hooks 75-125 (m=93.2, n=9). Spine band of tergite III straight for most of its length or only weakly curved outwards (if the line of the spine bases is continued posteriorly it cuts the posterior margin of the segment) (143c.jpg). Tergites IV and V with the armament arranged in longitudinal bands. ArR III-VI 0.85-1.17 : 1.0 : 0.24-0.40 : 0.07-0.30 (m=0.98 : 1.0 : 0.33 : 0.22, n=45). Longest spine III 93-135µm long; IV 60-120µm long; longest spine IV : III 0.54-1.08 : 1 (m=0.88, n=44). Postero-lateral comb of segment VIII 40-83µm wide (m=55.1, n=24); with 5-15 marginal teeth (n=26). Lateral taeniae of segments V-VIII: 0,0,1(2),5; usually one lateral taenia on segment VII situated on the posterior corner, the preceding seta short and hair-like, very occasionally taeniate. Ventral taeniate setae of segment VIII long, reaching well beyond the posterior margin of the segment (146b.jpg).
Anal segment: Armament of tergite IX of fine points, many grouped in twos or threes (146d.jpg). Fringe of anal lobe with 54-96 taeniae (m=67.7, n=47), forming a complete series (143d.jpg).
(Linked adult male: Langton and Pinder, 2003a)

Note: This is very similar to Tanytarsus inaequalis and often occurs with it, but the slight differences show up better in such mixtures facilitating identification. An additional character which can be of use in their separation is the colour of sternite VIII: in gregarius if there is a median transverse infuscation, the cuticle posterior to it is also a little darkened; in inaequalis there is usually a distinct broad transverse dark band (appearing inverted V-shaped in most mounts due to folding), the cuticle posterior to it being clear.

Species keys out at Page 484: Tanytarsini 125 Tanytarsus of the Text Key.

Widespread in Europe.
(For more information see module IdentifyIt – file: Chironominae).

Ecological notes
Lakes and pools.