Spiders are one of the most common, easily recognizable and beneficial of creatures. Despite this, many people have an instinctive fear of spiders and will not tolerate the presence of spiders in the home. This article will provide you with the information you need to help understand spiders and make decisions about whether to seek the help of pest control professionals if you have spiders in your home. The vast majority of spiders in Michigan are not venomous or dangerous,
Spider Life Cycle
Spiders are not insects. Spiders, like insects, are anthropods (invertebrate creatures with exoskeletons); or more specifically, they are a class of anthropods known as arachnids. Arachnids have eight legs and, unlike insects, have only two body segments (insects have three).
Spiders typically are born in the spring, as they come out of their egg sacs as soon as the weather gets warm. The mother spider may guard her young for a time by carrying them around on her back or building a protective “nursery web” for them. The spiderlings will eventually leave their mother to establish their own webs.
In order to grow, a spider needs to shed its exoskeleton, a process called molting. The spider will go through successive phases of molts before reaching adulthood and sexual maturity. Spiders at maturity can look vastly different depending on species and sex (most female spiders have larger abdomens than males in order to store eggs). There can be great variations of appearance even among spiders of a single species (the common house spider, for example, can be white, yellow, brown, black or any shade in between).
When a male spider detects the presence of a female, he will do an elaborate “dance” on the web to entice the female, even “plucking” the web like a harp. Spiders do not mate by intercourse; the male will eject sperm onto a ball of silk, then dip his pedipalps (the “feelers” near the mouth) into the sperm. Then he will insert his pedipalps into the female’s genital opening and “inject” the sperm into her abdomen, where she will store it until she is ready to lay and fertilize eggs (click here to see a video of the mating dance of the jumping spider).
When a female spider lays eggs, she will create an egg sac. Different spiders make different types of egg sacs. In general, the female will lay the eggs on a sheet of silk and fertilize them with the sperm stored in her body. She will then wrap the eggs in several layers of silk to protect them, creating the egg sac. Then the life cycle begins anew.
The lifespan of the spider can vary. Most common house spiders can live for one or two years, but some have been known to live for five. Some species of spiders can even live for twenty years.
The Amazing Spider Web
The most distinguishing characteristic of the spider is its web, though not all spiders make them. Spider webs are made of silk, an amazingly strong material. In its density and tensile strength it is comparable to high-grade steel and is half as strong as Kevlar. Despite this strength, it is remarkably ductile (stretchable); silk can stretch up to 1.4 times its relaxed length and not break.
Spiders produce webs from spinneret glands located on their abdomen. The webs are used for catching prey, but also as a home for the spider and a place for the female spider to deposit egg sacs. They also serve as means of transportation for spiders to cross between a distance too wide for them to leap across unaided.
Besides web-building, spiders also use their silk to “balloon”, a term describing the manner spiderlings use for dispersing themselves. Spiderlings will exude several threads of silk into the air that will be caught in upward drifts and will carry the spiderlings away. Though usually the spiders will only be carried a few yards, it is possible for them to travel many miles if caught in a strong updraft.
Spiders in the home
By and large people are familiar with some of the more well-known spiders like the tarantula or the black widow, but most spiders encountered in the home will not be of these varieties. Below are descriptions and information on the most common spiders people are likely to encounter in their homes.
Common House Spider
The common house spider (Parasteatoda tepidariorum) is found throughout North America. They vary in size from 6mm to 2.5cm and may be a variety of colors, though they always have rather dull hues, allowing them to blend into their environment. They feed on such household pests as flies, mosquitoes, wasps and ants. House spiders will bite if cornered or grabbed, but their bites are relatively non-toxic and no more painful than a normal bee sting. The designation “house spider” is also used to cover a wider variety of species commonly encountered by humans; all of the spiders listed below may sometimes be referred to as “house spiders” since they are found within human dwellings.
Like house spiders, wolf spiders may vary in size, though on the larger end they can be quite a bit bigger than house spiders, up to 1.2 inches; their bodies may be a little bit larger relative to other house spiders. Like house spiders, they may be any variety of dull colors, though they are usually some hue of brown. Wolf spiders are active, agile hunters. Rather than spinning webs and waiting for prey, the wolf spider hunts its prey, chasing it and pouncing upon it. Wolf spiders are very quick; even humans sometimes have a hard time when trying to whack them, since the spider is capable of dodging attacks extremely quickly.
Daddy Long-Legs (Cellar Spider)
Identifying the daddy long-legs can be difficult because people commonly use the name to refer to three different anthropods: the spider also known as the “cellar spider”, the crane fly (also known as the “mosquito eater”) and the opilione arachnid called the “harvestman.” Since crane flies are easily identifiable by their wings, and harvestmen live primarily outdoors under logs, it is usually the cellar spider that most people are referring to when they say “daddy long-legs,” since this spider is commonly found indoors, especially in cellars and basements.
Contrary to popular belief, the daddy long-legs (cellar spider) is not venomous. Daddy long-legs prefer to live on ceilings and will commonly make their webs in the corners of livingroom ceilings, but also in garages, cellars or under eaves. It preys on mosquitoes, other spiders and even other daddy long-legs if food is scarce. They are non-aggressive, will rarely bite and pose no significant danger to humans. However, many people are frightened by their appearance, especially their extremely long legs.
Orb-weaver spiders build the spiral wheel-shaped webs often found in gardens, fields and forests. There are over 10,000 varieties of orb-weaver spiders in the world; in fact, they make up 25% of all spiders worldwide. The orb-weavers are tremendous workers, sometimes building a new and complete web from scratch every single day. Orb-weaver spiders are also common in barns; orb-weavers do not generally take up residence in homes as often as house spiders and are usually not a problem.
Jumping spiders are a very large branch of the spider family known as Salticidae. Jumping spiders are common both indoors and outdoors throughout the United States. They take their name from their method of hunting prey by leaping quickly upon it, jumping up to half and inch and pouncing upon prey. Jumping spiders usually have larger eyes than other species and have more hair. They usually grow no larger than one inch and are a dull, earthy color.
Most people associate spiders with venomous bites, but the danger of spider bites is exaggerated. The vast majority of spiders are not dangerous to humans; only a small percentage if dangerous. All spiders, even venomous ones, are non-aggressive and will not (usually) bite unless they feel provoked or threatened;even then only the larger species are capable of piercing human skin with their fangs.
According to the Michigan Department of Natural Resources, there are only two species of venomous spiders found in Michigan: the brown recluse and the black widow. The brown recluse is not indigenous to Michigan and cannot live in temperatures colder than 40°F, so they are extremely rare in the state. It is believed that they have come in on trucks originating in the southern United States.
The northern black widow, on the other hand, is native to Michigan and can be found all throughout Michigan, especially in the western lower peninsula. The black widow is small, only about an 1/2 inch long (1.5 inches if you include the legs). They are entirely black save for a bright red, hourglass shaped marking on the abdomen of the female (note that the hourglass marking is broken in the middle). Males will lack this distinctive hourglass marking but may have red or yellow bands on their back or abdomen. Black widows are common around woodpiles; many encounters with this spider happen when people carry firewood into the house. They may also live under eaves, in boxes, outdoor toilets, meter boxes and other undisturbed places. Take extra caution when working in areas where black widows may live; make sure to wear gloves and pay attention. Black widows bite rarely, as they are timid and prefer to flee an encounter rather than bite. If you are bitten by a black widow, you will need to seek medical attention immediately. Their bites are quite painful and can cause acute latrodectism, a condition in which the spider’s venom spreads quickly throughout the body, causing constant, strong, painful muscle contractions in all the major muscle groups followed by severe cramping. These severe muscle contractions (a condition called tetany) may occur with dizziness, anxiety, tearing of the eyes, headache, tremors and joint pain. Though death is rare from a black widow bite, and though symptoms will usually dissipate within 3 days, medical treatment can considerably lessen the unpleasantness of the symptoms by use of muscle relaxers and antivenoms. Victims who are elderly, extremely young or very ill are at higher risk for more serious complications.
Dangers from spiders
Most people concerned about spiders in the home are worried about spider bites. Except for the rare brown recluse and the black widow, none of the other spiders in Michigan pose a threat to human health from their venom. This is not to say that other spiders will not bite; any spider will bite and even the bites of non-venomous spiders can be painful. Spiders will bite if they are picked up or handled, but most spider bites do not occur in this manner. A more common manner of getting bit occurs when people are bit in their sleep. A spider will be prowling about under the covers, attracted by the warmth and darkness. A person sleeping will unknowingly roll over or move and frighten the spider, which will then bite the sleeper before scampering away. The person wakes up with a painful bite, sometimes mistaking the spider bite for bed bugs.
Spiders eggs are also a threat, in the sense that a spider allowed to freely lay eggs in the home will only beget more spiders. The corners of ceilings and basements should be vacuumed regularly, as should dark areas behind dressers, the backs of picture frames or any other out of the way spot. Spider eggs sacs will appear as furry little white balls, usually a little smaller than a marble. The underside of outdoor eaves are also common locations of spider egg sacs. Destroying/removing spider eggs is essential to controlling spider populations.
For many people, the problem with spiders is simply their presence in the same living space as humans. Human beings collectively seem to have an innate fear of spiders, a phenomenon that has been noted by scientists. Arachnophobia, fear of spiders, is the most common of all phobias and is believed to affect 55% of women and 18% of men. Even for those who do not formally have arachnophobia, the presence of spiders in the home can be unnerving.
Benefits of spiders
Spiders can be quite beneficial to have around the home because they prey on other undesirable pests, such as mosquitoes, ants, wasps and flies. Some spiders will even prey on other spiders; for example daddy long-legs (cellar spiders) will eat black widows. Even the dangerous brown recluse spider eats cockroaches and silverfish. Spiders are numerous enough in agricultural fields (sometimes literally thousands or millions to the acre) that they serve to reduce pest insect numbers considerably. The world wide benefit of pest control by predatory insects and spiders together may exceed US $100 billion per year.
Getting rid of spiders
While it is difficult to ensure that you will never again see a spider in home, it is possible to utilize a combination of pesticide application and minor environmental modifications to greatly reduce the chances of having spiders in your home. Pesticide applications around doors and window sills can keep spiders at bay, while spot treatments throughout the home can take care of existing spiders. Increased vacuuming of corners and dark areas to destroy spider eggs is integral in keeping spider populations down. Reducing the amount of dark areas for spiders to hide in is also helpful, such as cleaning up dirty rooms, making sure laundry is not left out, etc. Make sure the layers of windows are intact and sealed correctly. Granular pesticidal applications around the foundation of the home may also help. In some cases where a spider problem has gotten out of control; a home that has been vacant for some time and homes near lakes are at greater risk, especially in cities such as Waterford, Pinckney, Ann Arbor and Belleville where there is a lot of water nearby. In these cases where there is a more serious problem, a surface-area pesticide to the outside of the structure may be necessary.
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