Four legged insects
Intro
In Leviticus 11:20-23, Moses tells the Israelites that all winged insects that "go on all fours" are unclean, and the Israelites are therefore forbidden to eat them. Bible skeptics love to criticise this passage, because insects have six legs, not four, which means either God is not inerrant, or the Bible is not his word. However, as this article will demonstrate, it is actually the ignorance of modern skeptics that shows, not the ignorance of Moses.
Praying mantis
The image to the left is a Vietnamese flower mantis. To the right is the lower half of an Iranian praying mantis. As you can see, while it has six "legs", two of those legs are used for a very different purpose. Praying mantises hold their front legs out in front of them in a pose that makes them look like they're praying, hence the name praying mantis. The front legs have sharp barbs, which are used to grip prey when it walks by. Only the other two pairs of legs are used for walking. A praying mantis, therefore, was unclean under Leviticus 11:20-23.
Brush-footed butterflies
Just like mantids, brush-footed butterflies use their forelegs for a purpose other than walking. Instead of feet, their forelegs have brushes of hairs that are used for smelling and for tasting. These forelegs are often difficult to see, making the butterfly appear to have only four legs. A brush-footed butterfly would therefore be unclean.
Crickets and locusts: The exception to the rule
Verse 21 says Yet among the winged insects that go on all fours you may eat those that have jointed legs above their feet, with which to hop on the ground. Crickets and locusts are specifically mentioned. The first two pairs of a locust's limbs are indeed used for walking, but the most prominant pair of legs are designed for hopping, not walking. And this is exactly what the passage says! It is absurd to claim that Moses did not notice this fact, or indeed that no one else did in thousands of years.
What is a leg?
A fundamental question in this issue is what is a leg? Modern science obviously classes all six limbs of all the insects described in this article as a leg, but is it really fair to try to enforce this kind of system onto the Israelites? The Israelites, of course, had a completely different definition of "leg". They tended to classify things according to their function, so only those legs used specifically for walking would have been classed as legs. Are a mantid's prongs really legs? Modern classifications say yes, but the Israelites, while they obviously knew about the existence of those limbs, would not have classed them as legs.
Conclusion
Moses made no error when he said some insects "go on all fours". Instead, he was using a different definition of the word "leg", and there are, indeed, insects that fit the definition of having four legs. It is the fallacy of equivocation to accuse Moses of being wrong because of this passage, and absolute arrogance to say that Moses should have used modern definitions when he wrote the law. Taking the Bible in its correct context, this is one scientific "error" that has been resolved.