They're all from the same chapter of the same book.
Bats & birds:
http://www.carm.org/diff/Lev_11_19.htm
Note that the defender claims that the Bible ISN'T a scientific text. Hmm.
Rabbits & cud: Leviticus 11:6
Insects with 4 legs instead of 6: Leviticus 11:21-23.
From your link, Thalos:
"Also, we must be aware that it is modern science that has a different classification system than ancient times. To the ancients, creatures such as a bat were considered birds since they categorized all flying animals as birds. If that is the category that they used, then they were correct. It is not an error. It is a difference of categorization procedures. The critic has imposed upon the ancient text a modern system of categorization and then said that the Bible is wrong."
What part of this explanation do you disagree with? Are you saying modern taxonomy is your basis for disagreeing with the Bible? I would call that a pretty weak, unsupportable argument.
The same site discusses rabbits.
Locusts: Perhaps the hind legs (hoppers) were not counted in the description. From a current web site (http://www.geocities.com/brisbane_insects/ScientificInsect.htm):
"There are great variations on insect legs. Cockroaches have three pair of strong legs and they run very fast. Grasshoppers have their last pair of legs modified and they can jump to start a fright quickly. Praying mantids have their front pair of legs like a weapon to catch prey. Dragonflies do not use their legs to walk but to capture insects and hold them under their mouths. Butterflies use their legs to taste the food. Besides, insect legs are also used for digging and swimming."
Note:
from:
http://en.wikipedia.org/wiki/Orthoptera
Taxonomy note
Note that the cricket suborder Ensifera will probably be given its own order soon, the Grylloptera. The Orthopterists' Society also recently (December 2005) decided upon a major change in the classificatory organization of the Ensifera.