National Geographic : 2018 Dec
EXPLORE WHEN SEEKING SEX, why wouldn’t the male Latrodectus geometricus spider go for the nice young females? They’re more fertile than their elders. They’ll mate more quickly, without an elaborate courtship. Last but not least: Young L. geometricus females don’t cap off a copulation by cannibalizing their date— while older females do. (That’s what gave the species its common name: the widow spider.) Given the obvious advantages, a research team in Israel expected L. geometricus males to prefer young females. To test that assumption, researchers set up spider orgies, offering males access to consorts of all ages. Their findings were published in Animal Behaviour. To get sex with an older female, a male might fight off many rivals or perform courtship gestures for up to six hours. At the magical moment, he’d place one of his two sexual organs into one of her two sexual openings—and she would start to eat him alive. If he survived, he might try to mate again or be too maimed to do so. In the study, when males had one-on-one time with females of different ages, the males mated with fewer than half the youngest females—but 100 percent of the oldest ones. Not one of the males that mated with the youngest females died from cannibalism—but more than half those that mated with the oldest females did. “We really don’t understand” males’ suicidal lust for older mates, says study co-author Shevy Waner. One theory is that mature females exude stronger sex pheromones, compensating chemically for what they lack in fertility and youth. —PATRICIA EDMONDS AND KATIE WATKINS PHOTO: JOEL SARTORE. ILLUSTRATION OF BLACK HOLE: NASA/JPL This brown widow spider was photographed at the Audubon Nature Institute. INSIDE THE ALMANAC A Galactic Directory Curious about our place in the universe or at least the Milky Way? National Geographic’s Almanac 2019 lists Earth’s dis- tance from other celestial bod- ies, in miles or light-years (LY): ASTEROID: 26,000 MILES An asteroid known as 2012 TC4, just 50 to 100 feet long, flew that close to Earth on October 12, 2017. COMET: 1.4 MILLION MILES In July 1770, comet Lexell (aka D/1770 L1) was six times as far away as the moon— but that’s still the closest recorded passage by a comet. NEXT STAR: 4.25 LY Proxima Centauri, our second nearest star (after the sun), forms a three-star system with Alpha Centauri A and B in the constellation Centaurus. HABITABLE WORLD: 4.25 LY In our nearest star’s orbit, an exoplanet—Proxima Centauri b—could have liquid water, based on its location and size. POSSIBLE SUPERNOVA: 150 LY The supernova candidate nearest to Earth is the smaller star in a binary system known as IK Pegasi. But at the velocity at which the system’s moving away from the sun, it should be safely distant if it explodes millions of years from now. PLANETARY NEBULA: 650 LY Not actually home to planets, this celestial object is the glowing remnant of a sunlike star. The Helix Nebula, in the constellation of Aquarius, is likely the closest to us. Beyond our Milky Way, the closest galaxy—if close is the right term—is Canis Major, 25,000 light-years from Earth. AVAILABLE AT SHOPNG.COM/BOOKS 2019 ALMANAC MAPS, FACTS, INFOGRAPHICS & MORE INCREDIBLE PHOTOGRAPHS HOT NEW SCIENCE 2019 ALMANAC ■ Exploration & Adventure ■ This Planet & Beyond ■ Life on Earth ■ The Science of Us ■ Yesterday to Tomorrow ■ Our World Combiningthelatesttrending topicswith evergreeninformation, NationalGeographicAlmanac2019isthe ultimateguidetoourplanet, bursting with factsandillustrationsthat willawe, inform, andinspire. US $19.99 / $25.99 CAN ISBN 978-1-4262-1981-8/PRINTEDINUSA EXPLORE THE WORLD THROUGHSTUNNING PHOTOS, ENGAGING STORIES, AND ILLUMINATING MAPS IN THIS NEWANNUAL FROM NATIONAL GEOGRAPHIC 2019ALMANAC A19_US_CvrSC_REL1_HY.indd 1 7/30/18 12:29 PM NGS16313-00_CoverUS_SC_4C_NT.pgs 07.30.2018 12:31 BASIC INSTINCTS HE LIKES HIS MATES OLDER. SHE APPRECIATES HIS TASTE.