During 2010's International Year of Biodiversity I lost count of the number of references to the quotation attributed to the geneticist John Haldane, who is said to have answered a clergyman's question about what his studies had taught him about the creator by saying: "He is inordinately fond of beetles." It is such a good line it really ought to have happened. And it raises a question about the very scale of biodiversity that ought to give creationists and biblical literalists pause for thought.

So far some 1 million species of insect have been discovered. Estimates of how many remain unknown vary between another million and 30m. Of these, some 400,000 are beetles – beetles in a wide array of shapes and sizes certainly, but still just beetles. A creator who made all of these but was so highly uninventive about body plans is puzzling. There are only 30 or so orders of insects, and the last was discovered nearly a century ago (there was a lot of excitement a few years ago, when a new order, the Mantophasmatodea, was erected, but that has now been demoted to a suborder). One wonders why a creator would make so many beetles but only 32 species of Zoraptera, or if beetles are so good, why the creator didn't make 300 more and not bother with the Notoptera at all. The argument for a creator's ineffability is unanswerable, of course, but mainly because it is not in any way explanatory. "Inordinately fond of beetles" just about covers it.

More problematic for literalists is the story of the flood. We are told the size of the ark (though it's not certain how big a cubit was) and, though 30 million insects (if we take two specimens of the median estimated number of species, although a fair number of insects are parthenogenic) may not take up all that much space, they are not negligible either. That, however, is the least of the problems – how did Noah manage to collect a pair of that many species, and where from? Was the Levant mega-diverse 5,000 years ago, or did Noah collect specimens all around the world? Given the havoc that introduced species cause in today's ecosystems, the latter seems more plausible, albeit improbable. Then there is the question of releasing them again.

Of course, parasites would be catered for on their hosts, though that means someone on the ark had lice and crabs. Arguably, the detritivorous and saprophagous species could jump straight on to the debris of the flood, but plants would have to be established for the herbivores (many of which are very host-specific), and then their populations established before the predators and parasitoids (also generally host-specific) could be released. For the species that feed on the live wood, fruit or seeds of slow-growing trees, the process would take years.

The logistics of ensuring the right combination of plants and animals in a given geographic region must have been immense. Of course, one way round this is the argument that a much smaller number of biblical "kinds" or baramins were carried, and that the species we see today developed from them. The problem with this lies in the sheer number of species – the fewer the number of baramins, the greater the rate of evolution in the past 5,000 years. If the "kinds" Noah carried were equivalent to genera, then some 90 species in the genus Psallus have differentiated in Europe alone. An omnipotent creator could, of course, facilitate Noah's task by suspending or changing the laws of nature. But that raises the question of why, in that case, he bothered with the whole ark thing to start with.

The biological argument that insects or beetles are similar because they have descended from a common ancestor that outlived (perhaps by chance) or triumphed over alternative designs seems simple in comparison. The idea that the myriad species we see today have spread because of the vagaries of colonisation, plate tectonics and changes in environmental conditions, and in response to the evolution of other groups (particularly the vascular plants), over tens of millions of years is positively economical compared with the idea that it all happened in 5,000 years or that Noah planted up every island in the Pacific.

Recognising that that argument is a logical fallacy, one is nonetheless impressed by the temerity of those who deploy it against the gnat of evolution while performing the mental gymnastics required to argue that the biblical account is somehow more straightforward.