The ships were designed by Yarrow to operate in shallow, fast-flowing rivers, with a shallow draught and a good turn of speed to counter river flow. They were fitted with two reciprocating engines operating two propeller shafts to offer some redundancy. The propellers were housed in tunnels to minimise the operating draught. The main armament consisted of two 6 inch guns in single mountings fore and aft.
Deployment
Aphis, Bee,Ladybird and Scarab were deployed to Port Said, Egypt in 1915-16, Gnat, Mantis, Moth and Tarantula were sent to the Persian Gulf in 1916. Glowworm, Cicala, Cockchafer and Cricket were deployed to the east coast of England in 1916 and had their main armament mountings modified to give higher elevation for anti-Zeppelin work. In 1919, during the Russian Civil War, Glowworm, Cicala, Cockchafer, Cricket, Moth, and Mantis served on the Dvina River, fighting in support of White Russian forces. Glowworms captain and some other crew members were killed when a nearby ammunition barge exploded. The crew of Cicala mutinied, as part of a wider wave of unrest in the Royal Navy, and five "ringleaders" were sentenced to death, later commuted to five years' imprisonment. Between the two world wars, the class were mainly used in the Far East and they were present during the Japanese invasion of China. In 1937, on the Yangtze river, the Japanese attacked, firing on her from a shore battery. A US gunboat, was also attacked, by Japanese aircraft, and sunk. Ladybird sailed the 20 miles to the scene of the sinking, took on board some of the Panay survivors and took them to Shanghai. Scarab and Cricket were off Nanking in 1937 as the Japanese started to bomb the city. In 1939, the original two 6 inch Mk VII 45-calibre guns on and Ladybird were replaced by more modern and 30 inch longer 6-inch Mk XIII 50-calibre guns from the decommissioned battleship. At the start of World War II, three vessels, Cricket, Gnat, and Ladybird, were transferred to the Mediterranean Fleet's Inshore Squadron. They joined the monitor and provided bombardment support for the 8th Army. Their shallow draught allowed them to act also as supply and landing vessels, able to get close-in to beaches. In June 1943, Aphis took part in the bombardment of Pantelleria.
: built by William Doxford & Sons, scuttled in Hong Kong 1941, captured and repaired by the Japanese and renamed Suma, sunk by mines in Yangtze River on 19 March 1945.
: built by Wood, Skinner & Co, scrapped in 1948.
built by Wood, Skinner & Co, briefly flagship of the British Pacific Fleet, expended as a target 1946