Why do translators use the phrase "insects that walk on all fours", even though insects have six legs?

Question

In Leviticus 11 when the Lord is giving the dietary laws to Moses, the NASB translation mentions four legged winged insects.

20 ‘All the winged insects that walk on all fours are detestable to you. 21 Yet these you may eat among all the winged insects that walk on all fours: those which have jointed legs above their feet with which to jump on the earth. 22 These of them you may eat: the locust in its kinds, the devastating locust in its kinds, the cricket in its kinds, and the grasshopper in its kinds. 23 But all other winged insects which are four-footed are detestable to you. - Leviticus 11:20-23 NASB (emphasis mine)

20 “‘All flying insects that walk on all fours are to be regarded as unclean by you. 21 There are, however, some flying insects that walk on all fours that you may eat: those that have jointed legs for hopping on the ground. 22 Of these you may eat any kind of locust, katydid, cricket or grasshopper. 23 But all other flying insects that have four legs you are to regard as unclean. - Leviticus 11:20-23 NIV (emphasis mine)

In these verses, the creatures specifically being referred to are

• locusts in its kinds
• devastating locusts in its kinds (aka katydids)
• crickets in its kinds
• grasshoppers in its kinds

and are labelled as insects by the English translators. When I read insect I immediately think of six legged animals, and the Merriam Webster dictionary gives two relevant definitions for insect.

1. any of a class (Insecta) of arthropods (such as bugs or bees) with well-defined head, thorax, and abdomen, only three pairs of legs, and typically one or two pairs of wings
2. any of numerous small invertebrate animals (such as spiders or centipedes) that are more or less obviously segmented —not used technically

All the animals specifically referred to are technically insects because they have six legs, but this is further confused when considering vs. 41-43, where the phrase "walks on all fours" is immediately followed by "has many feet". It makes sense to me that the translators are probably referring to the second definition though.

41 ‘Now every swarming thing that swarms on the earth is detestable, not to be eaten. 42 Whatever crawls on its belly, and whatever walks on all fours, whatever has many feet, in respect to every swarming thing that swarms on the earth, you shall not eat them, for they are detestable. 43 Do not render yourselves detestable through any of the swarming things that swarm; and you shall not make yourselves unclean with them so that you become unclean. - Leviticus 11:41-43 NASB (emphasis mine)

My question is why are the translators specifically using the phrases "on all fours" or "four-legged" alongside "many-legged" in the same context to refer to different animals simultaneously that in all of the specific instances have more than four legs? As someone who is not a translator but knows a fair amount about entomology, I'm curious to better understand the semantic domain of these words (insects, and swarming things) and phrases (four-legged, and many feet) from the original language.

Answer 1

If you read the complete verse of Leviticus 11:21, the total legs of a kosher flying insect הָע֔וֹף are 6 [legs] = אַרְבַּ֑ע Arba 4 [legs] + 2 Kra'ayim כְרָעַ֨יִם֙ Jointed [legs] above.

In Hebrew, the phrase " הָע֔וֹף הַהֹלֵ֖ךְ עַל־אַרְבַּ֑ע " means "insect that walks on four [legs]" in English. - Notice the additional 2 Kra'ayim כְרָעַ֨יִם֙ Jointed [legs] above the regular four legs for hopping.

Leviticus / Vayikra 11:21 [MT]

"However, among all the flying insects that walk on four [legs], you may eat [from] those that have jointed [leg like] extensions above its [regular] legs, with which they hop on the ground." ( אַ֤ךְ אֶת־זֶה֙ תֹּֽאכְל֔וּ מִכֹּל֙ שֶׁ֣רֶץ הָע֔וֹף הַֽהֹלֵ֖ךְ עַל־אַרְבַּ֑ע אֲשֶׁר־ל֤וֹ (כתיב אשׁר־לא) כְרָעַ֨יִם֙ מִמַּ֣עַל לְרַגְלָ֔יו לְנַתֵּ֥ר בָּהֵ֖ן עַל־הָאָֽרֶץ )

Answer 2

This is not a "phrase used by translators", it is the literal text, which says "holekh al arba" or "walk on four".

I don't think translators should change that to read "six" to aid our understanding, but should give a faithful literal translation, which they did.

Then, it is the job of interpreters to dig into semitic cultures and learn the background information necessary about how these ancient cultures viewed insects, in order to find out what was meant. For example, we read in the Word Biblical Commentary that by tradition, the two big legs on grasshoppers and locusts were not counted as part of the four that were walked on, but were considered different types of legs - "leaping legs", so that grasshopers had "leaping legs above the [walking] legs":

Members of the locust-grasshopper family actually have a third pair of long, jointed legs that are attached close to the neck, appear to be above the other legs, and are bent when the insect is in a squat position (Wessely 1846). The Priestly term kĕrāʿayim means “shins” in connection with a quadruped, that is, the lower part of the leg below the knee (see the NOTE on “shin,” 1:9) and, by extension, refers here to the saltatory legs of this creature (illustrations in VBW on Joel 1:4 or in EncJud, s.v. “locust”). Tg. Neof. renders accurately “leaping legs above their legs.”

Milgrom, J. (2008). Leviticus 1–16: a new translation with introduction and commentary (Vol. 3, pp. 664–665). New Haven; London: Yale University Press.