All Images: Rick Vetter except for center collage: top and bottom left: AdobeStock

Spiders are high on the list of homeowners’ concerns. Despite usually only causing messy webs or psychological issues, they come right after real pests like ants, cockroaches and termites on the list of creatures that generate the most calls. Identifying spiders properly is not an easy task. Many are generically colored in tans and browns and require the use of a microscope and some knowledge of spider taxonomy. This article hopes to cover some of the difficulties in proper identification of spiders of interest to the pest management industry.

BLACK WIDOW SPIDERS. Black widows are of great concern because their toxic bite can result in a doctor visit or even hospitalization. Although the adult females are very characteristic with their shiny black coloration and red hourglass on the belly, immatures (which are sometimes capable of biting) look very different than the mature female.

Fig. 1. An immature southern black widow spider, Latrodectus mactans, with red dorsal spots. When the spider matures, the dorsal abdomen will be completely black.

The southern black widow, Latrodectus mac-tans, starts off life with white stripes on a dark background color on the abdomen. As the spider matures, the black overtakes the stripes. However, remnant juve-nile coloration can result in a series of red dots in a line on the abdomen (Fig. 1). The southern black widow is most common in the southeastern quadrant of the United States.

Fig. 2. An immature western black widow spider, Latrodectus hesperus. As the spider matures, the white lines dissipate and the background coloration darkens, turning the abdomen solid black.

The western black widow, Latrodectus hesperus, is more troublesome to identify. When the babies emerge from the egg sac, they have white abdomens with small black dots. As they mature, white stripes appear over a tan or olive-green background (Fig. 2). The females eventually turn solid black with a red hourglass on the belly. Western black widows are found in the western half of the U.S., from desert to mountain habitat.

The juvenile coloration causes difficulty because of the striping but especially when there is red in the longitudinal abdominal stripe with a red hourglass. Homeowners sometimes get excited because they think they have found a mutant, a hybrid or even a specimen of the Australian red back widow (the last of which has never been found in North America).

BROWN WIDOW SPIDERS. Brown widow spiders, Latrodectus geometricus, are a relatively new pest control entity. This non-native species lived in Florida for decades but now is common in the Gulf Coast states and Southern California. When established, they become common urban pests.

Rick Vetter
Fig. 3. Brown widow spiders, Latrodectus geometricus, are difficult to identify due to great variation in coloration. However, their presence is much easier to verify by their spiky egg sac.

Brown widows exhibit tremendous abdominal color variation from cream to almost as black as a black widow, so it requires a great deal of experience identifying dozens of specimens before being proficient at brown widow identification of the spider. The best way to identify a brown widow infestation is by the spiky egg sac (Fig. 3), whereas, in contrast, black widow egg sacs are smooth surfaced. The brown widow is not nearly as toxic as black widows but because they have “widow” in their name, homeowners think they are dangerous and desire to have them controlled.

FALSE WIDOW SPIDERS. False widows of the genus Steatoda are common household spiders. False black widows, Steatoda grossa, are often confused for black widows, but they are chocolate brown in color and never have an hourglass. They are found in many areas of the U.S.

The noble false widow, Steatoda nobilis, often has a tan “house” pattern on the dorsal abdomen and is a recently established European spider in the San Francisco Bay-Monterey area, as well as San Diego and the Los Angeles basin.

Both of these spiders make egg sacs that look similar to cotton balls. Although neither spider is particularly toxic, rampant arachnophobia in Great Britain involving the noble false widow has caused the misinformed and unnecessary closing and fumigation of schools; it’s hoped these irrational actions do not duplicate in the U.S.

RECLUSE SPIDERS. Recluse spiders are rather easy to identify, but there is much misidentification of harmless spiders as recluses not only by the general public but also physicians, other medical personnel and even pest control professionals and entomologists. People in native recluse regions are usually very adept at proper identification; the misidentifications usually come from areas of the continent that don’t have recluses. For this latter group of people, if it is brown and has eight legs, it often is misidentified as a recluse spider.

The brown recluse, Loxosceles reclusa, is a tan spider and is correctly described as having a violin pattern on the cephalothorax (the body part to which the legs attach) (Fig. 4). However, many spiders have a dark pattern in the same area leading to misidentification as well as creating false confidence in homeowners’ ability to properly identify a spider as a recluse.

Fig. 4. Although brown recluse spiders, Loxoxsceles reclusa, have a distinct violin, many spiders have dark coloration, which causes non-arachnologists to misidentify harmless spiders as recluses. A more reliable identification feature is their pattern of six eyes.

A more diagnostic way to identify a spider as a recluse is to look at the eyes. Most spiders have eight eyes in two (or rarely three) rows. A recluse spider has six eyes in a U-shaped layout; a pair in front and a pair on either side separated from the front pair by a space. This will eliminate most spiders as non-recluses although one must be aware that spitting spiders (genus Scytodes) have a similar six-eye pattern, but its body is covered in spots, lines or is totally black. In addition, the southwestern recluse species (e.g., desert recluse, Arizona recluse) often have faint or no coloration in the violin area, so people using the violin as the identifying mark will misidentify a desert-living recluse as a non-recluse spider.

The brown recluse occurs from southeastern Nebraska to southwestern Ohio and south through Texas into northwestern Georgia, being common in the middle of its range and becoming rare on the fringes of its distribution. Five related recluse species have wide distribution in the deserts of the Southwest U.S.

YELLOW SAC SPIDERS. Yellow sac spiders (genus Cheiracanthium) are common household spiders and rather generic in coloration. While most are pale yellow to tan, they also can have green or pink abdomens depending on what they have recently eaten. They have eight eyes in two straight rows across the front of the cephalothorax and somewhat floppy legs. They make a little refuge (i.e., the sac) between two surfaces in cracks or crevices.

These spiders are of concern to the pest control industry because they are often involved in envenomations. The initial bite is painful like a bee sting, but most of the manifestations involve minor symptoms of pain, swelling, redness and itching that usually resolve on their own within a few days.

There are two species in the United States, both considered immigrants from the Eastern Hemisphere. They are found throughout North America but occurrence in a home will be more of a random event as opposed to an infestation, which can be treated by the pest control operator.

ORB WEAVERS. Orb weavers (family Araneidae) are annual spiders that start off life in the spring as minuscule babies. They grow quickly, mature and mate by autumn and females lay egg sacs before they die in winter. They make large Halloween-decoration type webs, often living in the eaves of homes and spinning new webs on a daily basis. Sometimes homeowners walk into the webs strung between two trees resulting in an unpleasant experience for both human and spider. Most requests for control of orb weavers come in late summer to early autumn when the females become large.

Orb weavers typically hang near the center of the web or in a corner waiting for prey to blunder in where the sticky silk threads retain the prey before the spider wraps it. There are dozens of orb-weaving species in North America and to identify them beyond family level requires a microscope and the abilities of an arachnologist.

Orb weavers are strictly outdoor spiders and can be a major nuisance around places with abundant insect prey such as water treatment or water control facilities. One such facility estimated that they were dealing with 100 million spiders in a large treatment plant. One mitigating factor for small infestations is that the spider is an annual creature, so they should disappear with winter. However, their babies will probably return in the spring.

Fig. 5. Wolf spiders have two large “headlight” eyes on their face with 4 small eyes below.

WOLF SPIDERS. Wolf spiders (family Lycosidae) occasionally get into homes, but usually it is a single interloper running through a kitchen. They are usually festooned in tans, browns and blacks. They are easily identified by their eye pattern; they have two large “headlight” eyes on the front of the cephalothorax with four small eyes usually in a straight line below (Fig. 5). Two additional large eyes are found further back on the cephalothorax. Their large headlight eyes give them excellent vision, so they can readily see you approaching with a rolled-up newspaper and will run away. Additionally, they are the only North American spiders that carry baby spiderlings on the mom’s abdomen.

There are hundreds of species of wolf spiders in North America and their similarity to each other make it difficult even for arachnologists to identify them beyond family level.

Fig. 6. Jumping spiders are compact, fuzzy and very cute. Their large front eyes rival human vision in acuity.

JUMPING SPIDERS. Jumping spiders (family Salticidae) are the most charismatic spiders, such that homeowners may describe them as fuzzy and cute. They have excellent vision. They have squat, tank-like bodies, can be colorful and maneuver like cats as they seek out and pounce on prey. Their excellent vision is manifested through large front eyes (Fig. 6). They have smaller eyes lateral to the large eyes and four more small eyes further back.

Similar to wolf spiders, there are many species of jumping spiders in North America and they are difficult to identify beyond family.

Rick Vetter is a retired arachnologist from the University of California, Riverside (UCR).