蟷螂

Either a compound of 鎌 (kama, “sickle”) +‎ 切り (kiri, “cutting; cutter”, the 連用形 (ren'yōkei, “continuative or stem form”) of verb 切る (kiru, “to cut”)), or of 鎌 (kama, “sickle”) +‎ キリ (kiri, onomatopoeia), where the kiri is imitative of the sound made by grasshoppers and katydids, and is found as a common element in the names of several insects of similar size and body shape. Compare 螽斯 (kirigirisu, “grasshopper; katydid”), 笹切 (sasakiri, “bush cricket; katydid”).

Considering the sharp forelegs of the mantis, the first derivation may be more probable.

The kanji are jukujikun (熟字訓), from Chinese 蟷螂／𬠅螂.

• (Tokyo) か​まきり [káꜜmàkìrì] (Atamadaka – [1])[1][2][3]
• IPA^(key): [ka̠ma̠kʲiɾʲi]

蟷螂(かまきり) or 蟷螂(カマキリ) • (kamakiri) 

1. a mantis (any of various large insects of the order Mantodea)
2. (by extension, from the slender build of the insect) a skinny person or horse
3. (rare) a fourspine sculpin, a fish of species Cottus kazika

   Synonym: 鮎掛 (ayukake)

As with many terms that name organisms, this term is often spelled in katakana, especially in biological contexts (where katakana is customary), as カマキリ.

For the fourspine sculpin sense, the more common kanji spellings are 鎌切 and 杜父魚.[1][4]

From Middle Chinese 螳螂 (MC dang ljang|lang).

• (Tokyo) とーろー [tòóróó] (Heiban – [0])[1][2][3]
• IPA^(key): [to̞ːɾo̞ː]

蟷(とう)螂(ろう) • (tōrō) ^{←たうらう (taurau)?}

1. a mantis

• 蟷(とう)螂(ろう)の斧(おの) (tōrō no ono): “the mantis's hatchets” → a metaphor for a futile endeavor; compare English piss in the wind, kick against the pricks, quixotic