mole cricket, cicada
蛄 centers on a specific insect: the mole cricket. The cicada meaning is a less common extension, but both refer to burrowing or loud insects.
蛄 combines the insect radical 虫 with 古, which likely provides the sound コ. The character was created to name a specific insect, the mole cricket.
The insect radical 虫 beside 古 suggests an old, ancient bug: picture a mole cricket that has been burrowing underground since ancient times.
For コ, imagine a mole cricket making a low 'co' sound as it digs: co -> コ, the call of this ancient insect.
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mole cricket (esp. the Oriental mole cricket, Gryllotalpa orientalis)
mantis shrimp (any marine crustacean of order Stomatopoda, esp. the species Oratosquilla oratoria); mantis crab; squilla
red swamp crayfish (Procambarus clarkii)
stonefly (any insect of order Plecoptera, esp. those of family Perlidae)
Japanese mud shrimp (Upogebia major)
being a jack of all trades and master of none
being a jack of all trades and master of none
caddisfly; caddis fly (any moth-like insect of the order Trichoptera)