Gut DNA from 200 Joro spiders finds a fly-heavy diet native orb weavers largely ignore

The load-bearing result here is the null one. If Joro spiders were pushing native orb weavers off their preferred prey, native diets should look different where Joros have arrived, and in this dataset they do not ^[6]. It is worth being precise about the shape of that comparison: it contrasts places with Joros against places without them, not the same places before and after. Nobody recorded which spider species lived in those spots, or in what numbers, before the invader turned up, which is why Jason Schmidt of the University of Georgia says the impact question is hard to pin down at all ^[12][4].

Gut sequencing also records what a spider caught, not what was on offer to catch. Two animals can eat different things because they hunt differently, or because the shared prey is abundant enough that neither is squeezed. Different menus are evidence against a food fight; they are not proof that the overlapping insects, which both groups do eat ^[4], are not the ones that matter when supply drops ^[5].

Then the denominators. More than 200 Joros came from 33 sites in Georgia and South Carolina ^[2], an average near six spiders per site ^[1], against a comparison group of more than 140 native orb weavers ^[3] - roughly 1.4 Joros examined for every native ^[3]. That asymmetry cuts one way on the headline number: the 26 prey species found only in Joro guts ^[5] is a richness count, and richness counts rise with the number of individuals you look inside. The bigger sample was the Joros' ^[6].

What the diet data do say cleanly is what the spiders were eating in the season sampled, and it was small and unglamorous. Schmidt describes a lot of little flies, prey he characterises as pests, and says that for the size of the animal the contents look like popcorn ^[9]. The monarch worry, which drove a good deal of the public alarm, does not show up: butterflies of any kind were not a large part of the diet ^[8]. The study reports a significantly different and wider Joro diet than the natives' ^[4][7], with leafhoppers and aphids among the prey natives left alone ^[5].

Space is the part nobody has resolved. Joro webs tangle with other webs in a style Schmidt calls quite different from other spiders', though native spiders turn up in webs right beside them ^[10], and he concedes that others may read the space question differently than he does ^[11]. Whether the species is an ecological threat remains open ^[13].

The practical edge of this is chemical, not ecological. Schmidt's advice is to skip broad insecticides, partly because no insecticide is labelled specifically for spiders ^[14] - so a yard sprayed to kill Joros is a yard sprayed at the flies and leafhoppers this study says Joros are removing, and at native orb weavers that already carry pesticide pressure ^[15].