mole cricket, cicada
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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.
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)
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.