Leviticus 11:21

על ארבע means UPON FOUR legs. ממעל לרגליו ABOVE ITS FEET — Quite close to its neck it has something like two feet, in addition to its real feet; when it wants to fly and to spring off the ground it presses itself strongly on the ground with those two knees and so it flies. There are many of these, such, as those which we call longouste (sea-locusts), but we are not expert in regard to them, — as to which we are not permitted as food, — because four characteristic marks of cleanness are mentioned by our Rabbis in respect to them, viz., four feet, four wings, and קרסולים, i. e. the כרעים mentioned here, and that their wings cover the greater part of them. All these characteristics are present in these which are found amongst us, but there are some of them which have a long head and there are some which have no tail, matters which do not affect the question of cleanness (Chullin 59a). It is, however, necessary in order that they shall belong to the clean species that they should bear the name חגב (Chullin 55b), and in this respect we do not know how to distinguish one from another [i. e. we have no tradition as regards to these locusts whether they belong to the species which was in olden (Talmudic) times called חגב or not, and consequently in spite of the other four marks of cleanness we cannot distinguish them from unclean locusts which also show the same marks but are unclean because they do not bear the name חגב].

Yet these may you eat of every flying creeping thing that goes upon four, which have legs above their feet, to leap with upon the earth;

אַ֤ךְ אֶת־זֶה֙ תֹּֽאכְל֔וּ מִכֹּל֙ שֶׁ֣רֶץ הָע֔וֹף הַהֹלֵ֖ךְ עַל־אַרְבַּ֑ע אֲשֶׁר־[ל֤וֹ] (לא) כְרָעַ֙יִם֙ מִמַּ֣עַל לְרַגְלָ֔יו לְנַתֵּ֥ר בָּהֵ֖ן עַל־הָאָֽרֶץ׃