Baetis maculosus

General appearance
Body size medium-small up to about 5mm long (excluding antennae & cerci)
Body color yellow brown; abdominal terga with distinctive markings

Head
Labrum with a pair of submedial setae and fewer setae (<6) situated on each side of midline
The details for mouthparts illustrated in the following pictures

Thorax
Hindwing pads present; villiopore present
All legs similar with dark markings:
3 dark marks on femora proximally, submedially & distally; 2 marks on tibiae proximally & apically; a pale mark on tarsi distally

Abdomen
Gills II - VII, single, tracheated but poorly seen branched tracheae
Darken markings on terga II, III, VII & VIII & a pairs of dots medially on terga II - VIII
Cerci length slightly longer than half of body length; medial filament slightly shorter than cerci, about 0.85 times in length

Legs (All of legs look similar)

 

Its mouthparts of labrum, mandibles, maxillae and labium are illustrated as follow (hypopharynx is excluded).

Labrum

Maxillae

Mandibles

Labium

 

Distribution:
In Hong Kong, specimens are recorded from Pui O, Sam Tsuen and Wang Lung Hang (Lantau Island), Tai Mong Tsai, Pak Tam Chung, Ho Chung and Sha Kok Mei (Sai Kung), Ha Wan Yiu (Tai Po), Shek Shan Tsuen (Lam Tsuen Valley) and Tan Shan River.

Reference:
Tong, X. & Dudgeon, D. (2014) A New Species of the Genus Baetis from China (Ephemeroptera: Baetidae) Entomological News 123(5): 333-338.

Remarks:
Larvae of Baetis maculosus can be distinguished from other baetids by its distinctive abdominal pattern.