Spiders! Eek! Just the word sends chills down your spine. They are creepy and scary, but most spiders serve a purpose other than causing terror to the homes they invade. In their natural environment (including human dwellings) spiders are important arthropod predators and serve a vital function in controlling insect populations. Actually, only a few pose any threat to human health. The brown recluse and the widow spiders are two well-known and highly venomous examples.
There are a little over 40,000 species of spider in the world, about 1,200 of which may be found in United States. They live everywhere, even inside homes and buildings. In fact, some spider species have become so adapted to conditions within human dwellings that they can no longer survive outside. Due to spiders’ reclusive habits, most people are unaware of how many spiders actually exist in a given environment at any time. A single acre of grassy field, for example, can contain up to two million individual spiders.
Biology and Description
Spiders are arachnids, related to mites, ticks and scorpions, which differ from insects in their body make-up in three important ways:
- Have only two body regions rather than three
- Have eight walking limbs rather than six
- Never develop wings, unlike many insects
Spiders are predators, feeding primarily on insects and other arthropods. All spiders predigest their prey by injecting or covering the prey with digestive fluids, after which they consume the liquefied meal. Spiders can survive for long periods of time without feeding, some have been kept alive for over two years without feeding.
Jumping spiders, huntsman spiders and wolf spiders actively search for or stalk their prey. Trap-door spiders hide and wait for their prey to pass too closely. Orb weavers build complex webs that trap flying insects. Most web-spinning spiders build and abandon several webs per year. The webs are produced by glands on the spider’s abdomen. The silk is a liquid that is shaped by the appendages as it is excreted. A special type of silk is sometimes used as a parachute by spiderlings for dispersal or adults to travel long distances.
Spiders reproduce by laying eggs in a silken egg sac and it is either carried around by the female or hidden in the web. Large spiders can produce several hundred eggs inside an egg sac. The eggs hatch in about two to three weeks after deposited. Most young spiders mature to adults in about one year. Male and female spiders live separately and only come together to mate. Males are usually smaller and color-marked differently from females.
Spiders usually remain hidden and do not seek out and bite humans unless provoked. All spiders produce venom, but only a few can pierce human skin, and even fewer are considered dangerous to humans.
Most spiders are considered beneficial because they feed on insect pests and other spiders. If insects that serve as spider prey are not plentiful in a home, spiders are less likely to infest a home.
Non-chemical control of spiders is usually quite effective in reducing spider populations. Outside lights should not be left on at night because it attracts large numbers of flying insects which cause more spiders to hang around. Trash, lumber piles, bricks, weeds, and outside structures should be cleaned regularly because they are good breeding places. Egg sacs should be destroyed.
Chemical control of spiders is difficult because web-spinning spiders do not tend to contact treated surfaces. However, dust formulations can be used because dusts tend to cling to spider webs for long periods of time. When spiders chew their webs to recycle the silk they consume the toxicant and die. When spraying enclosed areas, care should be taken so a spider agitated by the spray does not drop onto the person spraying.
It is important to save any biting spider so it can be identified later. Most spider bites are not dangerous, but medical care and advice should be sought in any case of a suspected spider bite.
- Southern Black Widow- found outdoors in protected places. Around houses it is found in garages, storage sheds, crawl spaces, furniture, ventilators and rainspouts.
- Northern Black Widow- Mainly found in forests. Spins irregular, loosely woven webs 3 to 20 feet about the ground
- Red Widow- Makes its web off the ground in palmetto habitats and only found in sand-pine scrub associations. Web is spread over the fronds.
- Brown Widow- Most common on buildings. Also found on bridges and fences. Egg sacs look like an old naval mine or sandspur.
- Strong neurotoxic venom that can be deadly. However, death can be avoided if consulted by a physician and treated promptly.
Widow spiders are shy and will not bite unless aggravated. If you suspect a widow spider has bitten you, capture the specimen and consult a physician.
- Not aggressive unless provoked.
- Venom contains toxin that directly affects contacted tissues rather than the nervous system.
- Recognized by having a dark violin-shaped mark located behind the eyes.
- Medium sized spider about 1/4 to 1/2 inch in length
- Natural habitat is along the Mississippi River valley, Northwestern Arkansas and Southern Missouri.
If you suspect you have been bitten by a brown recluse, collect the spider and consult a physician immediately.
- Weighs 2-3 ounces and has a 10-inch leg span.
- Dense covering of stinging hairs on the abdomen
- Hairs can cause skin and eye irritation and may also provoke more severe allergic reactions
- Usually live in burrows in the ground
- Tropical species can require up to 10 years to mature to adulthood. Females in captivity have been known to live more than 25 years.
- Males often do not eat after reaching maturity and live for only one year or less.
- Can be kept as a pet, but a quality tarantula-keeping manual should be studied before purchasing a specimen.
It is important to become educated on spiders so that you know what to look for when determining if one is venomous. Only a small number of spiders can be harmful, so the next time you see a spider and want to freak out, just remember to stay calm. The spider doesn’t want to be bothered by you as much as you don’t want to be bothered by it.
Learn more about spiders and spider control by clicking here.
Chris Vann- Extension Agent- Agriculture/4-H