Latrodectus geometricus is also known as the brown widow spider, gray spider, geometric button spider, brown button spider and the house button spider. Discovered by C.L. Koch in 1841, it was originally described from specimens taken in South America. However, this species is now generally believed to be endemic to Africa.
Latrodectus is a Greek word that means “biting in secret,” referring to the initial painlessness of the spider’s bite that often goes unnoticed until later, when symptoms appear. Latrodectus is a Genus of cosmopolitan spiders of the dipneumomorph family Theridiidae (the comb-footed spiders) of the order Araneae, which includes most of the well-known venomous spiders commonly called black widows. Latrodectus has 31 recognized species worldwide, five of which are found in the United States. Four of these species are native — and one, the brown widow spider, was introduced.
The brown widow spider was first reported in the United States in 1935, in Florida. For a long time, this invasive species remained obscure in Florida, where it existed in isolated localized populations. In the mid- to late 1990s, there appeared to be a rapid range expansion in Florida, which was possibly attributed to a number of years with milder winters. This species now is reported to be the most common spider found around homes and workplaces in Sarasota County, Fla. (Sarasota.ifas.ufl.edu/IPM/BrownWidow.htm, accessed on Feb. 21, 2015).
Specimens of this spider have been observed living in the wild in Southern California. High populations of this species in this area live in close association with humans. It was reported previously the brown widow spider prefers to live in human habitations (Ebeling, W. 1975. Urban Entomology. University of California, Division of Agricultural Sciences. p. 330). If this was the case, its present habitat preferences in Southern California indicate evolution, adaptation and habitat expansion. Invasive species in new environments often exploit available habitats in their area of colonization.
The brown widow spider is found in the Southeastern, Southern and Southwestern regions of the United States. In addition to Southern California, it has been documented in Alabama, Arizona, Arkansas, Colorado, Georgia, Hawaii, Louisiana, Mississippi, Nevada, New Mexico, Oklahoma, South Carolina, Tennessee and Texas. It first was reported from a school campus in Torrance, Calif., by the author in 2003 (“Brown widows get a lesson in IPM,” Pest Management Professional The Buzz e-Newsletter. Web Exclusives, June 1, 2003). Because of the secretive nature of this spider and the varied habitats it occupies in close association with human habitation and workplaces, its geographic distribution and abundance in the United States is likely to be much more extensive than what’s reported.
Hiding out on the patio
The spider is timid and reclusive, ensconced in secretive and secluded places during daylight hours. Its small, nondescript web, which is located in protected, out-of-the way places, is often littered with dust, leaves, and other wind-blown debris ensnared within it, giving the appearance of an old web that was abandoned by a previous occupant (Fig. 1). Various kinds of miscellaneous clutter and materials stored around buildings in Southern California, as a result of human activity, are likely to harbor this spider. Plastic plant pots and trash receptacles with downward curved upper lips provide ideal harborages because they protect the spider from the elements.
By taking up residence in, on or under plant pots, the spider renders itself highly conducive to being transported in potted agricultural and landscape plants, which are commonly moved by gripping them under the lips, and unprotected fingers inadvertently can squeeze a spider living under the curved lips, tempting a defensive bite.
Brown widows are also commonly found under outdoor furniture, as well as in and around barbecue grills. It’s also postulated that an important factor in the brown widow spider widespread distribution in the United States is transportation by vehicles (Sarasota.ifas.ufl.edu/IPM/BrownWidow.htm, accessed Feb. 21, 2015).
The unusual prey
On Feb. 12, 2015, I noticed a large larva of Cotinis mutabilis hanging about 8 in. off the ground in a spider web between two 15-gal. plastic plant pots on my patio in Ontario, Calif. Adults of C. mutabilis are also known as the figeater beetle, green fruit beetle, fig beetle and June bug (Coleoptera: Scarabaeidae: Cetoniinae). The Cetoniinae comprises a group of beetles commonly called chafers, because many feed on pollen, nectar, and petals of flowers. Figeater beetle larvae are large, up to 2 in. long. The plump, creamy white grubs with a brown head are colloquially known as crawly backs. Equipped with six small prothoracic legs that are useless for locomotion, they roll onto their backs and propel themselves upside down, using the stiff, dark hairs on their backs to gain traction.
Many children are intrigued and fascinated by this mode of locomotion, and crawly backs generate tremendous excitement when their back-crawling is demonstrated to a classroom full of students. When at rest, the grub curls in a firm C-shape.
The larvae are found in the soil in places where high organic matter exists, such as decaying animal manure, compost piles, under decaying mulch and leaves and under piles of lawn clippings. I have compost and mulch piles in my garden, and I commonly encounter crawly backs when turning these piles. However, in the 23 years I lived at this location, I’ve never encountered one of these grubs crawling on the surface of the soil during the day or night. Skunks and raccoons love to dine on these fat larvae, and they often dig for them in the soil, causing damage to turf and landscapes (Fig. 2).
Crawly backs are lumbering grubs, and it would be hazardous for them to expose themselves on the surface of the ground. If a grub is exposed when turning the soil, it will quickly burrow back into the substrate and disappear below ground.
The plant pots where this spider was located had soil in them left over from last year’s planting, but no plants were present in the pots at the time of this discovery. I do not believe the larva emerged from the soil of the pots and fell out into the spider’s web below because the soil level in the pots was 2 in. below the lip of the container. Given the mode of locomotion of crawly backs, a specimen is not likely to surmount this smooth surface gap and crawl out of the pot.
To catch a predator
When I first discovered the grub hanging in the spider’s web, I poked it several times with a dissecting needle, but it did not move. It might have been envenomed by the spider to subdue it. Even though it was moribund, it was still fresh and pliable. Careful observations during daylight hours did not reveal the presence of a spider. Because of the presence of a small web, though, I suspected that a spider was responsible for this entrapment.
Experience with the western black widow spider (Latrodectus hesperus) in Southern California informed me the best time to look for a possible assassin was during the night. Female black widow spiders are known to avoid light during the day and remain hidden in protected retreats. Subsequent nocturnal inspections during five days revealed a spider with a red hourglass marking on the underside of its abdomen spending considerable time on the C. mutabilis grub (Figs. 3 and 4).
When trying to photograph the spider on the larva in darkness, I focused a flashlight beam on it. After a few minutes, the spider crawled away from its prey and headed back into its retreat under the lip of the plant pot. Perhaps it assumed daylight arrived and it was time for it to seek shelter. Once the flashlight was turned off, it took the spider about 15 minutes to return to its kill.
I continued to observe the scarab larva at intervals over the course of five days, when daytime temperatures in the area exceeded 80°F. I never saw the spider visit its prey during daylight hours. I originally thought this spider was an immature specimen of L. hesperus because juveniles of this species exhibit tremendous variation in color patterns.
But on Feb. 18, 2015, I tilted the plant pot on its side and was able to clearly observe the spider’s lair. A small segment of web containing six egg sacs was teased out from under the lip of one pot (Fig. 5). The egg sacs confirmed that this spider was L. geometricus. This spider constructs egg sacs having characteristic silk spikes covering their exterior. It is important to look for the unique egg sacs of the spider when trying to confirm a determination in the field because this species, in its juvenile and adult forms, exhibits remarkable polychromatism. Black forms of this spider have been reported in the literature, though I have yet to encounter this variant in Southern California. The black forms can be confused easily with females of the western black widow, making it all the more important to inspect for the characteristic spiky egg sac that is indicative of L. geometricus.
The big question
How did a large, soil-inhabiting grub find its way into the web of a brown widow spider to become its prey? Comb-footed spiders construct irregular, tangled, three-dimensional scaffold webs that have no pattern or shape. The silk strands of the web are extremely strong and elastic, and they can be plucked like guitar strings without breaking them. The dragline silk of black widows is strong and tough. The silk produced by L. hesperus has been investigated with the goal of producing a synthetic spider silk that could be used to make lightweight superstrong body armor, components of medical devices and high-tech athletic attire (Newsroom.ucr.edu/1612, accessed Feb. 21, 2015).
Black widow spider web silk is anchored sometimes to the ground, where it forms trap lines to entangle ground-crawling prey that trip the lines. The victims are sometimes yanked further up into the web, where the web inhabitant apprehends them. If this is the case, it could explain how a large, heavy figeater beetle larva found itself in the web of a brown widow spider
8 in. off the ground.
The L. geometricus spent considerable time at night on her beetle grub for five days, and I am convinced she fed on her victim for an extended period of time.
Many spiders commonly feed on arthropods and various insects, but these opportunistic predators will capitalize on other prey that becomes available. The unique case described here is evidence of that.
Dr. Hanif Gulmahamad, BCE, PCA is an urban and structural entomologist and consultant based in Ontario, Calif. He can be reached at email@example.com.
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⦁ In Lakeland, Fla., there was a report of a brown widow spider killing a small southern toad, Bufo terrestris, found in its web. It could not be determined whether the spider fed on the toad. Source: FloridaNature.org
⦁ A brown widow spider killing and feeding on a 5.5-in.-long Aurora house snake was reported in South Africa. Source: Dailymail.co.uk
⦁ Several years ago in Southern California, I was shown a photograph of a female Latrodectus hesperus with a young mouse tangled in her web. There was a mouse nest nearby containing several live juveniles. A portion of the spider’s web was anchored to the mouse nest. —Heather Gooch
It is common to confuse strength with toughness when comparing spider silk to other materials. Spider dragline silk has exceptional mechanical properties and high tensile strength and extensibility (sometimes called ductility, whereby some can stretch five times their relaxed length without breaking). Spider silk can absorb considerable energy before breaking, which is defined as toughness combining strength and ductility. When compared weight for weight, spider silk is stronger than steel, but not as strong as Kevlar; however, it is tougher than both.
The toughest spider silk known to man is produced by an orb-weaver species, Darwin’s bark spider, (Caerostris darwini). This spider silk is more than twice as tough as any previously described silk, and more than 10 times tougher than Kevlar.
In 2011, designers Simon Peers and Nicholas Godley created a cape from the silk of more than 1 million female Madagascar golden orb spiders (Nephila madagascariensis). The cape is naturally golden in color, and took more than four years to create. To learn more, visit GodleyPeers.com/press.html. —Heather Gooch