Four Spiders to Keep Your Eye On

By |  September 1, 2009

By: Rick Vetter

In previous articles, various spiders of concern to the pest management industry have been discussed. All have been either medically important or at least medically implicated at one point in the past. These included the brown recluse (PMP, June 2008), black widow (PMP, Sept. 2008), hobo and yellow sac spiders (PMP, Dec. 2008).

In this article, a smattering of other spiders are discussed, all which are harmless or are of minor medical concern. Interestingly, all of these spiders, which are common enough to require occasional control measures or are at least noticed by the average homeowner, are non-native species that are now flourishing in North America.

Brown Widow

The brown widow spider, Latrodectus geometricus, is related to the medically important black widow spider. It’s not nearly as toxic, however, as its better-known relative. A native to either Africa (most likely) or South America (less likely), the brown widow has, for many decades, been restricted to Florida. In the first part of the 21st century, however, they expanded their range to include coastal areas from South Carolina to Texas and urban southern California.


Brown Widow | Latrodectus geometricus

The brown widow is bedecked in tan and brown mottled coloration with an orange hourglass on the ventral portion of its abdomen. A series of brown and white spots along the abdomen runs on its top with three diagonal lines on the sides. One of the most identifiable aspects of brown widows is the egg sac, which has small silk spines poking out of its surface. No other urban North American spider makes an egg sac like the brown widow’s, making it one of the few examples where identification can be confirmed without seeing the actual spider.

In most cases, bites from a brown widow don’t produce extreme manifestation of envenomation similar to black widow bites. The most typical reactions caused by verified brown widow bites are pain when it happens, as well as a small red mark. There has, however, been one report of a verified bite that required hospitalization. Because this spider has the word widow as part of its name, it will generate concern from homeowners even though it is not as dangerous as a black widow.

These spiders are most often found in places that offer some harborage like under wood or potted plants, in debris, in pipes of fences and bicycle racks. Control would be best by spraying upwards under overhangs and in holes.

Woodlouse Spider

Woodlouse spiders, Dysdera crocata, are commonly found in homes and gardens throughout North America. Originating in Eastern Europe, they have spread throughout the world. The spider gets its name from its prey, the woodlouse, also known as sow bugs, isopods and roly-poly. They’re common in many parts of the United States and have only recently been found in decent numbers in the Pacific Northwest.


Woodlouse | Dysdera crocata

The woodlouse spider is rather distinctive in its coloration, with a dark cinnamon colored cephalothorax and an elongate abdomen, which varies from gray to tan. It has long fangs, which it uses to kill its prey by reaching underneath the rolled up creature and injecting venom. It has six small eyes scrunched together near the front of the cephalothorax. The eyes are rudimentary and probably only allow the spider to detect shadows or determine light from dark.

The bite of a woodlouse spider is rather benign to humans. There is, however, some pain from the mechanical fang penetration. The effects are usually gone within an hour. Control issues would be similar to that of typical spiders. This species does not usually show up in abundance, but can cause concern when it does.

Cellar Spider

Cellar spiders are one of the most ubiquitous spiders found in and around homes throughout North America. They have long, thin legs and hang upside down from flimsy webs. They’re often referred to as daddy-long-legs. One must be aware, however, this is a different creature than a daddy- or granddaddy-long-leg, which belong to another distinct grouping of arachnids.


Long-Bodied Cellar Spider | Pholcus phalangioides

The most common and widespread species is the long-bodied cellar spider, Pholcus phalangioides. Originally from Europe, the long-bodied cellar spider has been in the Americas for centuries. It has an elongate tannish-gray abdomen with no other markings. It also has a darkened pattern around the eyes that is frequently mistaken for the violin of a brown recluse, causing it to be misidentified, leading to unnecessary concern.

In the southwestern portion of the U.S., a Mediterranean species, the marbled cellar spider, Holocnemus pluchei, has become well established from the San Francisco Bay area, south to San Diego along the coast and east to Arizona. This spider also has an elongate abdomen with mottled coloration with a dark brown sternum and dark brown longitudinal stripe on its belly. From Florida to Texas, another cellar spider, Crossopriza lyoni, has become established and congregates around buildings in large enough numbers to elicit pest control measures. It has a truncated abdomen that looks like someone hacked off the posterior end.

As their name implies, cellar spiders, especially the long-bodied cellar spiders, are commonly found in the semi-subterranean basements of homes where they leave unsightly cobwebs in corners and by windows. The marbled cellar spider is commonly found under house eaves, in corners inside the house and under outdoor porch overhangs. Their populations can result in dozens to more than 100 spiders inhabiting the outside of a single home. These spiders cause no appreciable damage, but they do make aesthetically unsightly webs.

Spraying the spider in the webs should result in control. Sweeping away old spider webs reinforces to the homeowner that the area has been treated. It also allows pest management professionals to reassess how well the treatment worked on subsequent visits. One useful aspect about controlling cellar spiders is that they carry their egg sac, with the eggs surrounded by a few strands of silk, in their fangs. Therefore, vacuuming spiders carrying eggs will also eliminate a portion of the next generation.

Common House Spider

The common house spider is another European native, which has become almost ubiquitous throughout North America. It’s currently known by the scientific name of Parasteatoda tepidariorum and was recently changed from the well known but equally tongue-twisting name of Achaearanea tepidariorum. Similar to the long-bodied cellar spider, it has been in North America for centuries, spreading throughout the continent.


Common House Spider | Parasteatoda tepidariorum

It is in the same family as the widow spiders so it has a similar globular abdomen and hangs upside down in its web. The common house spider is colored in splotchy patches of tans and browns. It also makes the haphazard tangle of silk similar to widow spiders, leaving cobwebs in windows to collect dust after it leaves or dies.

In locations where it has access to external material, it will collect a few small leaves and incorporate them into a silken retreat with an open bottom in which it hides during the day. Gently squeezing the retreat from the top will cause the spider to escape or drop out of the bottom. The common house spider makes an egg sac that looks like a dirty tannish-brown ball. Control measures used for widow spiders should eliminate these spiders as well.

You can reach Vetter, an entomologist with the University of California-Riverside, at vetter@ucr.edu.

This article is tagged with and posted in Brown Widow Spiders, Cellar Spiders, Hobo Spiders, Spiders, Woodlouse Spiders

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