It was definitely a beetle (judging by the hard, non-overlapping wing cases, or elytra), but I don't think it was based on any particular species of real-life insect (let alone one that existed during the time of the dinosaurs). It had a little horn on its nose like a rhinoceros beetle (think Dim from
A Bug's Life) or some other member of the scarab family, but its defense mechanism of squirting liquid from its abdomen was reminiscent of
bombardier beetles. However, in real life, that would have been a far more unpleasant experience for Cera, as a bombardier beetle's spray is in fact the result of a complex chemical reaction within the insects body, the product of which is boiling hot as well as very smelly. (The beetles also discharge their spray in a series of high-speed bursts, rather than a steady stream.) There are many other kinds of insects that exude noxious liquid when threatened, but I'm not sure if any of them squirt it like the beetle in LBT.
Could be a beetle maybe, or a Locust. -_-
I can tell you for certain that it wasn't a locust; the swarming leaf-gobblers in LBT V were locusts. A locust is really just a phase in the lifecycle of certain species of grasshoppers that occurs when a population becomes overcrowded; regular physical contact with one another stimulates them to metamorphose into a gregarious form that can fly long distances. (
This video clip, which I originally saw on the National Geographic Channel, shows an entomologist demonstrating how you can artificially induce a grasshopper into becoming a locust simply by stroking its leg for five seconds once a minute for four hours.)
Maybe just a bug? 
Keep in mind that there are around 1 million named species of insects alive today alone (and that's not counting the ones that have yet to be discovered or scientifically described); I don't think “just a bug” would be a satisfactory answer.
: On the other hand, although I like to use it as a generic term for creepy crawlies as much as anybody, “bug” in the technical sense refers to members of the order Hemiptera; insects with sucking beaklike mouthparts and forewings that overlap one another when closed (aphids, stinkbugs, shield bugs, assassin bugs, cicadas, bedbugs, scale insects, water bugs, etc.). That would narrow it down a little, but it's a moot point, considering I think the insect in question was a beetle.
Forgive me; I can't stop myself from spouting insect trivia. I just love bugs!
