Some miniature-sized brown male spiders in Georgia might be annoyed if they paid the slightest attention to humans and our obsessions with the news.
Recent stories have made much of the “giant” jorō spiders invading North America from East Asia, some large enough to span the palm of a hand. Lemon-yellow bands cross their backs. Bright red bits can add drama, and a softer cheesecake yellow highlights the many joints in the long, black legs.
The showy giants, however, are only the females of Trichonophila clavata. The males are hardly mentioned except for what they are not: colorful or large. An 8-millimeter male spider helmet is barely half the length of small females. Even the nickname of the species ignores the boys. The word joro, borrowed from Japanese, it translates to such unmanly terms as “courtesan”, “maid of honor” and even “tangled or tied bride”.
Mismatched sexes are nothing new for spiders. The group shows more extreme size differences between known sexes among land animals, says evolutionary biologist Matjaž Kuntner of the Laboratory for Evolutionary Zoology in Ljubljana, Slovenia. The most dramatic case Kuntner has heard of comes from arachnura logio scorpion spiders in East Asia, with females 14.8 times the size of males.
With such extreme size differences, mating conflicts in animals can turn violent: females cannibalizing males and so on (Serial number: 11/13/99). However, to Kuntner’s knowledge, jorō spiders do not engage in these extremes of “sexual conflict”. being male simply half the size or something like that could account for the relatively peaceful encounters.
When it comes to humans, these spiders don’t bother anyone who doesn’t bother them. But what a show they make. “I have dozens and dozens in my garden,” says ecologist Andy Davis of the University of Georgia in Athens. “A large net can be 3 or 4 feet in diameter.” Joro spiders have lived in northeast Georgia since at least 2014.
These new neighbors inspired Davis and college student Benjamin Frick to see if the newcomers handle the chills better than an earlier invader. trichonophila clavipes, its more tropical relative also known as the golden silk weaver. (The jorō can also weave yellow-dyed silk.) The showy females and drab males of the earlier arrival have not left the comfortable southeast they invaded at least 160 years ago.
Discovering the resistance of the jorō involves taking the pulse of the spider. But how do you do that with an arthropod with a hard exoskeleton? A spider’s heart is not a mammal-like lump that circulates blood through a closed system. The jorō pours its blood-like fluid through a long tube open at both ends. “Think of a garden hose,” says Davis. He measured the heart rate of monarch caterpillars and found a spot on a spider’s back where a keen-eyed observer can count the beats.
Female jorō spiders packed in ice to simulate cold stress kept their heart rates 77 percent higher than one that stood still. T. clavipes, the tests showed. Verification of the jorō’s oxygen use showed that women have about twice the metabolic rate. And about two minutes of freezing temperatures showed better female survival (74 percent vs. 50 percent). Laboratory tests used only the suitably large jorō females, though the male’s ability to function in random cold snaps could also be important.
Furthermore, sightings of jorō in the southeast so far suggest that the most recent arrival needs less time than its relative to make the next generation, an advantage further north. Adults do not need to survive the deep winter in any case. Mom and Dad die, in November in Georgia, leaving behind their hundreds of eggs packed in silk to weather the cold and storms.
Reports on the citizen-observer iNaturalist site suggests that in Georgia, jorō spiders already cover about 40,000 square kilometersDavis and Frick report on February 17 in physiological entomology. Sightings now extend to Tennessee and the Carolinas. But how far big moms and little dads will go and when, we’ll just have to wait and see.