Why does Rashi classify a fly as having four legs

There’s a Rashi on this week’s parsha that has bothered me for years and nobody can give me a good answer for it so I’m turning to my fine friends in the CR for assistance. In Vayikra 11, pasuk 21 it speaks of shratzim that walk on 4 legs but have 2 jumping legs. Rashi differentiates between the longer stronger legs designed for leaping and the other 4 shorter legs which serve the sole purpose of walking. So while modern-day biologists simply classify all insects as including the characteristic of having 6 legs without regards to their specific purpose, Rashi clarifies that the Torah does indeed differentiate legs according to purpose. Therefore even though a locust or grasshopper may at first glance have 6 legs, in the Torah’s perspective it only has 4 which are it’s walking utensils.

The problem is that the passuk right before that talks about shratzim that walk on 4 stam, indicating that they don’t have an extra set of specialized limbs such as “jumping legs” and the first example Rashi states is flies (zvuvim). However flies have 6 legs and they use all 3 pairs of them for walking. Now you may have seen a fly rubbing it’s two front legs together (apparently part of how it cleans itself), however upon observation one can see that they do the same with their rear pair of legs so you can’t say that the front pair of legs are specialized and the rear 2 pairs are just for walking.

It seems like all 3 pairs of a fly’s legs are equally intended for walking so how can Rashi term it as an animal that walks on 4 when it actually walks on 6?