Review

Alien Empire (BBC1), which continues to treat the audience as if it had learning difficulties, last night featured the most disgusting restaurant in the world, a small establishment in which herds of cockroaches scampered across the gingham tablecloth, juicy caterpillars munched on the salads, butterflies fed in the fruitbowl, and houseflies slurped up their lunch through mouths ribbed like a hot- water bottle.

It looked as if conversation would be barely audible above the scutter and drone of insect activity, but this spot enjoyed its queasy distinction only for a short while. Even as your stomach was settling, you were shown how a certain rainforest beetle dines out on the humid dung of the howler monkey - Le patron excrete ici. Almost all of them have takeaways, rolling their glutinous find into small balls and trundling them across the forest floor, out of the reach of rivals.

Alien Empire is full of wonders, wonderfully filmed. But its entire approach implies the opposite - that without the elaborate horror-movie conceit in which the series is wrapped, we would somehow be indifferent to what it has to show us. This seems to be bad faith, at the very least. What, for example, was truly memorable from last night's episode? The lurid contrivances of the director, bathing his subjects in glaring red light (thus obscuring their natural colours) or tweaking up the soundtrack (robber flies "scrambling to intercept" dubbed, incredibly, with faint engine noises)? Or the startling images of evolution's obsessive perfectionism? The camouflaged insects that replicated every vein and blemish of the leaves they sat on; the spider that wove a pattern of dappled sunshine into its web to persuade passing butterflies to land; the assassin bug which used the sucked husk of a termite to lure others out of hiding, exploiting their instinct for tidiness.

This evidence of evolution's astounding power to create complexity begs many questions, but instead of attempting to answer them, Alien Empire wastes ingenuity and talent on a garish fairground facade. Not for the first time, I felt I would happily trade density and ingenuity of image for some density and ingenuity of argument.

In The Detectives (BBC1), you just get density: the thick gormlessness of Bob and Dave, blundering their way through yet another cack-handed investigation. The Detectives is, essentially, a kid's programme that's been allowed to stay up late: for all the references to drugs and sex, the comedy revolves around two proxy children getting into trouble with grown-ups (the equally dense Superintendent Cottam). Perhaps it is the brat within, but I have to confess that it is also, in its silly way, quite funny.

Last night's episode began with the accidental killing of a rare white- flippered Galapagos turtle (the boys disturbed its delicate digestion by feeding it with peanuts and Kit-Kats), a plot-line which allowed Jasper Carrott to give an eerily accurate impression of a turtle's face. It ended with a drug investigation in a girls' school: "It's a plant," protested the girl in whose locker a package of marijuana had been found. "We know it's a plant," replied Dave, giving an eyebrow-shrug of exasperation, "we're drug-squad officers - it's all green and spikey." They get away with jokes this corny because of the broad amiability of the programme, a transmitted pleasure in its own elaborately worked stupidity.

I wasn't sure about the faint whiff of sexual abuse that pervaded the latter half, with much lubricious speculation about young girls in school uniform, all of whom appeared to be below the age of consent. But even that off-note was made innocuous in the end: "Nothing wrong with a spring- and-autumn relationship," says Dave, after being rebuked for his fantasies. "Autumn?" Bob says, "Dave, you're Boxing Day - hung-over, short and boring".