The Joro spider, Trichonephila clavata, (Fig. 1) is a native of Japan and east Asia that was first documented in the US in 2014 in NE Georgia (Fig. 2). The initial infestation was centered around Braselton and Hochton, GA along I-85. By 2022 the spiders had spread about 75 miles in all directions from that initial detection (Fig. 3). The native range of these spiders in Asia extends from southeast Asia northwards through a swath of eastern China, the Korean peninsula and all but the northernmost island of Japan, and westward to India and the foothills of the Himalayas. Given that distribution, there seems to be no obstacle to the Joro eventually expanding its range to include all of GA and the southeast, and most of the rest of the eastern US as well.
Description
Adult female Joro spiders are very large and colorful, with a body length that can exceed 1” (Fig. 1A). The cephalothorax is silver or white above and the abdomen is bright yellow with teal colored bands (Fig. 1A). The underside is black and white checked with red splotches near the tail end (Fig. 1A). The black and yellow banded legs are up to 3” long (Fig. 1). The egg mass is fuzzy, and off-white in color (Fig. 4A). Immature Joros are much less colorful and can be difficult to differentiate from other web spiders (Fig 4B-F), but begin to acquire their adult colors in mid-summer (Fig. 4). Females are easily recognizable by mid-August (Fig. 4G). Males are not nearly as striking as females and may not be recognized as the same species by many. They are much smaller and more slender, with drab brown, yellow and black coloration on the abdomen (Figs. 1A and 5).
Besides their size, the most striking feature of the Joro is the web. Young spiders spin silk that is clear and looks much like any other web spider silk, but as they grow the silk becomes thicker and stronger. Mature females spin silk that is yellow or golden in color and very strong and sticky. These webs may span 10’ or more with support strands that can reach >20’ and stretch between the tops of large trees (Fig. 6).
Life Cycle
Like many of our native web spiders, Joros spend the winter in the egg stage. Females deposit their eggs in the fall, in batches of several hundred to more than 1000 in silk covered egg masses that they attach to leaves, tree bark, or structures (Fig. 4A). Eggs hatch in April – May. The spiders spend the summer growing and begin to mature in August and September (Fig. 4). There is just one generation per year.
Control Options
The most direct way to get rid of problematic spiders is to kill them. The manual technique of wrapping them up in the web and stepping on them is very effective. Simply destroying the web is not effective, as they rebuild in short order. Moving them to another area where they are less problematic can work but that has to be a good distance away or they will come back. A rake, a broom, or a stick can be used for wrapping the spiders up and they all work with some limitations. The higher up the spider is, the better the chance it will end up on your head. It is probably better to ignore the ones that are more than about 10′ up and just concentrate on those that are actually in the way.
A series of spray trials were conducted using readily available products bought at a local garden center. All products had “Spider” on the label as opposed to more generic “Pest” or “Insect”. The spray trials were interesting, and several products were found that are very effective at killing individual spiders including a couple that are fairly non-toxic and safe to use. Only the aerosols designed to target wasp and hornet nests have the range to reach a web up under the eaves of even a tall one-story house. The aerosol Black Flag Spider and Scorpion Killer (a.i. lambda-cyhalothrin 0.03% and prallethrin 0.025%) was 100% effective. An aerosol called Zevo Spider and Wasp spray was very effective (>97% mortality) also. The Zevo has geraniol and cinnamon oil as active ingredients and has the added benefit of smelling pretty good. The pre-mixed (RTU) pyrethroid (Sevin brand spray is 0.002% lambda-cyhalothrin) and Green Light Insecticidal Soap (in a manual spray bottle) were also effective (>80% mortality). Both of those products require that you spray from a foot or so away from the target, so that’s a drawback if you really don’t want to get close to the spider. Two or three squirts with a spray bottle are effective on small to medium spiders, but larger spiders require 5 or so. The aerosols (Black Flag and Zevo) were effective with just a brief blast. Dawn dishwashing soap at 1% solution in water was not very effective (40% mortality).
Many other homeowner products have synthetic pyrethroid insecticides as the active ingredients (cypermethrin, lambda cyhalothrin, bifenthrin, etc.) and can be purchased as RTU or in concentrate form that the homeowner can mix in a pump-up style garden or backpack sprayer. Previous experience has shown these ingredients are all effective at killing spiders if applied directly to the target. Once dry on the substrate (leaf, wall, etc.) they are not very effective for web spiders because they do not eat or come in contact with the residues. Pyrethroids are also toxic to lots of other things besides bugs and spiders. Spraying one spider at a time minimizes the impact, but those are the same chemicals used by pest control companies to treat for mosquitoes and other bugs in the yard so if you are not comfortable with that approach then maybe that’s not the best choice.
Our recommendation for most homeowners who are somewhat tolerant of spiders is to remove and kill any spiders that set up webs on or adjacent to porches, walkways, decks, windows and doorways (Fig. 7) – in other words, anywhere contact with the webs is inevitable. On the periphery of the yard or in shrubbery beds where people do not walk they can be left alone. The two places where no one should allow the webs are around pollinator/flower gardens and bee hives (Fig. 8A).
Of course, many professional lawn care companies offer pest control as an option. These services typically use pyrethroid insecticides (cypermethrin is common, but so is bifenthrin and several other products; the active ingredients almost always end in -thrin) that are very effective either as a spray or as a fog for mosquitoes. Remember that area wide sprays and fogging will kill many other insects including pollinators and beneficial predators and parasites that help keep pest insects in check. Scale insects, in particular, have been shown to increase in number and damage after these treatments. Please carefully read the label of insecticide products because label is the law.
