Funnel-web males send knockouts in air.

Male funnel-web spiders seem to be wafting some kind of knockout gas toward the females they court--a tricky gambit since a laboratory test shows the substance can also knock out the male.

Since there's a fine line between a female's next mate and her next meal, spider courtship requires precise diplomacy, explains Fred D. Singer of Radford University in Virginia. The funnel-web spider, Agelenopsis aperta, sidesteps this problem. During courtship, the female curls into a harmless cataleptic state for at least several hours, sometimes days, enabling a male to mate without being eaten.

In their search for the knockout mechanism, Singer and his colleagues let males flirt with females confined in cages that kept the genders at measured distances from each other. Males managed to send the females into a cataleptic state without touching them, but their ability to do so declined substantially as distances exceeded 4.5 centimeters.

That finding suggests airborne compounds, says Singer. In the early stages of trying to identify the active ingredients, he and his colleagues exposed both male and female spiders to heated tissue from male spiders. The females swooned as expected, but so did the males.

In natural settings, males seem to avoid such mishaps, Singer reports. However, laboratory setups with dense spider webs may highlight the underlying risk. In one such colony, he noticed courting males succumbing to their own incapacitating chemistry.