Eek! A Spider

Wolf spider (Photo: Flicker sharing, Thomas Shahan)

Arachnophobia, a fear of spiders, is a common and powerful fear. Many people fear spiders more than other common arthropods like cockroaches, centipedes, and wasps. We all hear stories about the danger of being bitten by black widow, brown recluse, or hobo spiders. All too often, this fear is the result of a lack of knowledge about spiders, and the role they play in the environment.

What’s a Spider?

Spiders are arachnids, in the order Araneae, with four pairs of legs, no antennae, no wings, and only two body regions (compared with insects that have 3 pairs of legs, antennae, often winged, and three body regions). The head and thorax of spiders are combined into a cephalothorax which is attached by a narrow pedicel to an unsegmented abdomen. The abdomen has spinnerets at the posterior end, from which silk for spider webs is spun.

Spiders are predatory, preying on many kinds of insects and other arthropods. Spiders have a pair of hollow pincers, called chelicerae, connected to poison glands -- while all spiders have poison glands, only a few are poisonous to humans. When spiders capture prey, their bite injects venom and digestive fluids, paralyzing their victim. With the prey immobilized, the spider sucks out the innards leaving only an empty shell. Other spiders crush their prey, bathe the tissues with digestive fluids, and crew the entire mass until only a little ball of indigestible material remains. Small wonder spiders are a favorite theme for Halloween and other horror venues.

A pair of pedipalps on the head, resembling legs, distinguish female spiders, which are also usually larger than males. Females spin silken egg sacs in which they lay masses of eggs. After a period of time, young spiderlings hatch and emerge. Young spiders resemble adults, growing by periodically molting their outer shells 4-12 times to reach the adult stage. If you see what looks like a dead spider, it’s often only the molted shell.

Spiders Eat as much as Humans?

Spiders prey upon insects in vast quantities. In research recently published in the Science of Nature, Martin Nyffeler of the University of Basel, in Switzerland, and Klaus Birkhofer of Sweden’s Lund University, attempt to put some numbers on spiders’ dining habits. Their conclusion was that there are 25 million tons of spiders around the world and that, collectively, these arachnids consume between 400 million and 800 million tons of animal prey every year. This puts spiders in the same predatory league as humans as a species, and whales as a group. Each of these groups consumes some 400 million tons of other animals annually.

Spider Identification

Spiders are abundant with some 50,000 known species. Spider identification keys in on such physical traits as the position and number of eyes, the overall shape, length of legs, and form of the spinnerets, as well as behavior, specifically web-spinning or not. 

Web Spinning Spiders

Black Widow Spider. Photo by Chuck Evans, Wikimedia Commons

Black Widow Spider

The black widow spider, and its relatives in the genus Latrodectus, are easily recognized by the reddish or orange hourglass marking on the underside of the abdomen. Black widow spiders get their name from the fact that the female frequently eats the male after mating, a practice not uncommon to several other species of spiders. In general, a docile, non-aggressive spider, unless the female is protecting the egg sac. The bite is a neurotoxin and very painful. The pain occurs less at the actual bite but rather in the abdomen and limbs. Physiological effects are an accelerated heartbeat, increased blood pressure, breathing difficulties, and paralysis. Although the bite of a black widow is rarely fatal it is important to seek medical attention. Antidotes are commercially available.

The common house spider is usually the spider most often encountered indoors. 

It is found worldwide and is common throughout the United States and Canada. 

House spiders

House spiders are among the most common spiders found in buildings. Two of their lateral eyes touch each other on each side of the cephalothorax and are well separated from the other four eyes. Female house spiders have bodies which are 1/8-3/8 inches long and the abdomen is often covered with dirty whitish or brownish hairs arranged somewhat like chevrons. House spiders spin irregular sheet webs in protected places in the corners of rooms, ledges, windows and under furniture. Unlike black widow spiders, males and females are often observed living together in the same webs. Webs of house spiders often have dead insects entangled in or lying beneath them.House spiders

Some common household spiders, Genus Steatoda, are in the same family as the black widow, but are not poisonous. Adult females resemble the black widow in size and shape; however, there is no red hourglass marking on the underside of the abdomen and there is often a whitish T-shaped marking on the topside of the abdomen.

Large yellow-silver and black banded Argiope spiders spin large orb webs in habitats ranging from gardens to canyon creek bottoms. Photo by Dennis Schotzko, University of Idaho. All rights reserved.

Orb-weaver spiders

Orb-weaver or garden spiders are generally large, with bodies ½ -1 inch long. They often have conspicuous black, white, yellowish or orange markings. These common spiders are often seen in late summer or fall. They are able to construct large, conspicuous webs with a central hub from which spokes radiate. All this is constructed in less than an hour. The female sits in the hub, waiting to detect movement that signals prey has been captured. After mating, the female seeks a protected place to lay a cluster of eggs, some 300 to 800, which will hatch the following spring.

A funnel web spider

Funnel web spiders

Funnel web spiders all have eight eyes about the same size and slightly separated, bodies about ½-inch long, and usually two dark longitudinal stripes on a grayish cephalothorax. The most distinguishing characteristic is a long posterior pair of spinnerets. Funnel web spiders spin flat webs of silk which extend into tubes or funnels into which the spiders retreat for protection, hence the name. The webs are often found in shrubbery near buildings, or in the angles of windows, doors or buildings. They reach the peak of their population in late summer and fall and often enter buildings at that time. Most funnel-weavers die after the first frosts. Winter is passed in the egg stage.

The hobo spider is marked with a series of light colored triangular loops on the abdomen. Typically, the first mark has a smudged appearance (A). The next three loops form triangles complete with two side borders and a bottom (B). The marks that follow are incomplete; they have two sides but lack the bottom border (C). Definitive identification requires microscopic examination by a trained expert. Photo by Edward John Bechinski, University of Idaho.

Aggressive house spider (Hobo)

The aggressive house, or hobo, spider (Eratigena agrestis) is becoming one of the most common spiders in the Northwest. This spider was first reported in the Seattle area in 1930. It is a prevalent spider in basements and in window wells of houses. It rarely climbs vertical surfaces and is usually found only on the ground or lower floors. The hobo is a long-legged, swift running member of the funnel web spider family. The brown abdomen has a distinctive yellowish chevron pattern. The legs are a uniform brown without the darker brown bands that other nonpoisonous funnel web spiders have. It is not harmful to humans. 

Non Web-spinning spiders

The brown recluse spider is tan-brown with a violin-shaped dark mark behind the head. The neck of the violin points backwards toward the abdomen. Photo Kansas State Research and Extension

Brown recluse spiders

Brown recluse spiders are easily recognized by a key characteristic: six eyes arranged in three pairs forming a semicircle. The fiddle on the top side of the spider is not always clear and found in many other spiders. Most other spiders have eight eyes variously arranged. Adult female brown recluse spiders are about ½-inch long (legs excluded); males are somewhat smaller. Both female and male brown recluse spiders can bite people and inject venom. Individuals react differently to bites. A stinging sensation is usually followed by intense pain. A small blister arises and a large swollen area around the bite becomes congested and swollen. While bites of the brown recluse are generally not fatal, they result in a local necrotic lesion that heals slowly, leaving an ugly scar. There are other spider bites that give a similar reaction, and these are often misdiagnosed by well-meaning physicians as brown recluse spider bites. Presently Brown Recluse spiders are not documented in Montana and the Northern Rockies.

Wolf spiders are large, spiny-legged, brown and grey spiders that dart across the ground when disturbed. The have characteristic arrangement of two large eyes over 4 smaller eyes. Two other eyes (one on each side of the face) are out of view. Photo by Craig R. Baird, University of Idaho.

Wolf spiders

Wolf spiders are medium to large spiders, and are usually hairy, brown or black, with long legs adapted for running. They have good eyesight – an adaptation for chasing down their prey, paralyzing it and feeding. Webs are not used by wolf spiders. Female wolf spiders carry the egg sac attached to their spinnerets until the eggs hatch. They then carry the young spiderlings about on their backs for a time. Some of the largest spiders encountered in Montana are in this group. This group is very mobile and may be found moving into houses in the fall in search of prey. Wolf spiders are medium to large spiders, and are usually hairy, brown or black, with long legs adapted for running. They have good eyesight – an adaptation for chasing down their prey, paralyzing it and feeding. Webs are not used by wolf spiders. Female wolf spiders carry the egg sac attached to their spinnerets until the eggs hatch. They then carry the young spiderlings about on their backs for a time. Some of the largest spiders encountered in Montana are in this group. This group is very mobile and may be found moving into houses in the fall in search of prey.

Jumping spiders can be identified by their two large eyes that point forward like headlights on the face. Together with four smaller eyes on the face and one on each side of the head, these give jumping spiders the acute vision needed to hunt and capture prey. Photo by Dennis Schotzko, University of Idaho. All rights reserved.

Jumping spiders

Jumping spiders, like wolf spiders, do not spin webs to capture prey, but rely on quickness and visual acuity. Jumping spiders and wolf spiders have two eyes much larger than the other six, probably an adaptation to help them better see their prey. Jumping spiders are small to medium sized spiders, usually stout bodied, short legged and hairy. They frequently have contrasting black, reddish, or yellowish markings. They are very agile, pouncing and feeding on small insects about the home. They are often seen on screens or near doors or windows.

Crab spiders are often seen on blooming flowers where they capture nectar-feeding insects. Photos by Dennis Schotzko, University of Idaho. All rights reserved.

Crab spiders

Crab or ambush spiders are somewhat crab-like in shape and walk sideways or backward. They are medium sized and often brightly colored, with abdomens that are usually wide at the posterior end. The two front pair of legs are usually longer and stouter than the two hind pair and crab spiders often hold their legs poised to trap insect prey. They have eight relatively small, well-spaced, light colored eyes. Crab spiders are usually found outside in gardens and landscaping where they spin no webs but forage for their prey or lie in ambush on blossoms or other parts of plants. They are able to gradually change colors to match flowers for camouflage.

Daddy Longlegs

Daddy longlegs, also known as harvestmen, are not spiders, but in the order Opiliones comprising more than 6,000 species of arachnids. Their extremely long narrow legs and small bodies, that appear as a single segment, are characteristic. Daddy longlegs are harmless, lacking fangs and do not produce venom. Some species have mouthparts that form an enlarged pincer-like tooth that might slightly pinch, but none bite. Daddy longlegs resemble cellar spiders (photo, page 7), a long-legged spider, whose jaws are too weak to bite people. A simple way to distinguish these two species is web-or no web. Daddy longlegs do not spin webs and are seen running agilely over the ground; in contrast, cellar spiders do spin webs, where they are almost exclusively found. If they are knocked off their web, cellar spiders move clumsily on the ground.

Management- What to do about spiders?

In general spiders do much more good than bad. Where spiders cannot be tolerated – for instance, where black widow or other spiders pose a threat to individuals or pets, a broom or vacuum cleaner used to dislodge, dispose, or move the offending spider outside should suffice. Spiders found outside under eaves and in corners of residences can be removed/relocated by use of a broom. Keep spiders out of your home by:

ü  Weather-strip and caulk around doors, windows, and utility lines.

ü  Fill in cracks in siding and around the foundation; reset loose bricks and siding.

ü  Keep debris and wood piles away from buildings.

ü  Inspect firewood for spiders and egg sacs before bringing indoors.

ü  Reducing clutter in storage spaces as boxes and other objects stored in undisturbed basements, crawlspaces, garages, and closets provide hiding places.

Protect yourself from spider bites by wearing gloves when working around potential spider habitats, such as gardening, moving wood piles or wood debris, or placing your hands into dense vegetation. Wear long-sleeved shirts and pants if you work around crawlspaces or cedar-shake shingled rooftops where spiders can hide.

Most spider bites cause only minor injury. A few spiders can be dangerous. In the United States, these include the black widow spider and the brown recluse spider.

Spider Bites: First Aid

Seek emergency care immediately if:

·         You were bitten by a black widow or brown recluse spider

·         You are unsure whether the bite was from a poisonous spider

·         You have severe pain, abdominal cramping or a growing ulcer at the bite site

·         The person who was bitten isn't breathing

To take care of a spider bite:

·         Clean the wound. Use mild soap and water and apply an antibiotic ointment.

·         Apply a cool compress. Use a cloth dampened with cold water or filled with ice. This helps reduce pain and swelling. If the bite is on an arm or leg, elevate it.

·         Take an over-the-counter pain medication if needed. If the wound is itchy, an antihistamine (Benadryl, Chlor-Trimeton, others) may help.

·         Your doctor may recommend a tetanus booster shot if you haven't had one in the last five years.

Spider Sniffing

Ever wondered how many spiders might be watching you? If you have a flashlight and darkness, you can spot them by the green glow of their eyes.

Many animals that hunt at night have an iridescent layer behind their retinas called a tapetum, including cats, dogs, racoons and some birds. It improves their night vision, and also causes “eyeshine.” Spiders commonly have eight eyes and four of those eyes have tapetum, so go find them.

To go spider sniffing, hold a flashlight level with your eyes. Spider eyeshine is returned at a relatively narrow arch so this flashlight position is key to spider detection. Sweep the light across outside lawn, foliage, and other dark spider-lurking spots. If you see a bright point of eerie green light, that’s your spider.

Arachnophobes, consider this: without spiders, there would be an awful lot more other creepy-crawlies around.

Sources

“Spider Bites”, Economist, March 18, 2017.

Edward John Bechinski, Dennis J. Schotzko, and Craig R. Baird.  2010. Spiders around the home and yard. Idaho Extension Service. 28 pages

Mayo Clinic. Spider Bites: First Aid. https://www.mayoclinic.org/first-aid/first-aid-spider-bites/basics/art-20056618

Montana State University Extension, 2014. Spider Identification and Management. MT19921OAG. 4 pages. Several species accounts taken verbatim from this publication.

Longbodied cellar spiders are the most common spider found in basements. Photo: Joseph Berger, Bugwood.org