Simply walking on the webs of female black widow spiders can provide males with chemical cues telling them if their potential mates are well fed or not, according to researchers at the Arizona State University.
The researchers found that males used chemotactile cues on females' webs and silk to assess whether they recently caught food or if they're well-nourished.
Acting selectively plays to the males' advantage since well fed females show more interest in mating and are less likely to consume their sexual partners when compared to starving females, reports the Discovery News.
The black widow's namesake derives from the females' occasional trick on males: As a male spider approaches a female in her web to court her, she'll eat him instead. Researchers have observed females cannibalizing males after copulating, but not much beforehand until now.
If female spiders are hungry, they'll skip sex altogether to eat males, especially if there is a surplus of them. This is why courting behaviour in black widows is particularly extensive -- males not only have to maneuver around the web to show they're not prey, they also must demonstrate why females should reproduce with them.
But the experiments show that males don't blindly crawl into just anyone's home. In one setup, virgin males were placed within proximity to two types of empty webs: those of well-fed females and those of starving females.
Through chemical and architectural cues on the webs alone, males began courting on the webs of well-fed spiders more often than starving ones, just as the team hypothesized.
Next, researchers did the same experiment but this time with females present. Still, males approached the well-fed gals more often for mating -- for good reason, too. Zero well-fed females attacked the males before sex, while some 70% of starving spiders did.
A third experiment switched the females and their webs, presenting males with well-fed females on starved spiders' webs and vice versa. The males paid more attention to females' presence than webs alone, still approaching females with full stomachs more often.
To test whether chemical cues affect courting behaviour, the team wrapped different females' silk around toothpicks in a separate experiment. Even then, they found that males preferred the silk from well-fed spiders.