While many people have "Arachnophobia" (an instinctive or learned fear of spiders), the vast majority of arachnids are actually harmless to us. Spiders are very sensitive to vibration and their first instinct is typically to run and hide when disturbed. The majority of accidental bites occur when spiders in clothing or shoes are squished by the wearer. Usually, this only results in temporary redness and itching. Only two species of spider in Missouri are considered medically significant: the brown recluse and female "black widow."
True spiders are members of the order Araneae. They have 8 walking legs with tiny retractable claws on each foot. Most have a cluster of 6-8 eyes on the top of their head. These eyes provide them with great depth perception since they combine multiple layers of vision into one–like 3D glasses. Orb weavers build elaborate hanging webs with sticky silk. However, not all spiders build traditional webs, some are opportunistic ambush predators. They sometimes make "web carpet" security systems with vibration alarm "trip wires." Sitting quietly on the silk–their body, covered in sensitive hairs, tells them when a potential meal is walking by.
Spiders are beneficial because they feed on many common insect pests including aphids, caterpillars, leafhoppers, grasshoppers, mosquitoes, and flies. A recent study estimated arachnids consume 400-800 million metric tons of prey each year and over 90% of that biomass is invertebrates. According to Lund University, "Spiders eat more insects than people eat meat and fish." Without these important biological control agents, pest numbers would increase exponentially.
One of the most easily recognized "spiders" is the "daddy longlegs" or "harvestman" (Leiobunum ventricosum). Contrary to popular myth, "daddy longlegs" have no venom and no fangs, nor can they produce silk! In fact, the harvestman has only one body segment, instead of two, so it's not a "true spider" at all. They belong to the order Opiliones, not Araneae. They are omnivorous scavengers that feed on decaying organic matter or small insects. People often handle daddy longlegs with their bare hands, knowing they are completely harmless.
Common house spiders (Parasteatoda tepidariorum), cellar spiders (Pholcus spp.), crab spiders (Xysticus spp.), and yellow garden spiders (Argiope aurantia) are frequently seen in gardens or residential areas. While the common house spiders may look scary with a body shape similar to the infamous black widow, its grey coloration, white marbling and banded legs make it easy to distinguish. It feeds on flies, crickets, wood louse, and other household pests. Cellar spiders have tiny tan bodies, long hair-like legs, and black-spotted knees. Often, they are seen hanging from loose strands of silk on the ceiling--waiting to catch a house fly. Crab spiders have a unique ability to change color like an octopus–camouflaging themselves to blend in with flower petals as they await their next meal. The yellow garden spider is perhaps the largest and most beautiful orb weaver in the state. Females with striking yellow, black, and blue coloration are easily spotted resting in the center of their giant web.
Common species of spiders that ambush their prey include jumping spiders, wolf-spiders, and the Missouri tarantula. Adult jumping spiders are typically black in color and 1 inch (2.54 cm) in length. They have green pedipalps and a white patterned abdomen that resembles a face. As the name implies, they can "jump" (up to 50 times their body length!).
Spiders from the "wolf" family (Lycosidae) received their name because they are frequently seen prowling the ground in search of bugs to eat. They can attain sizable leg spans of 4 inches (or more) and are often mistaken for tarantulas.
There is one species of tarantula found in Missouri, Aphonopelma hentzi. It is brown in color, lives in burrows, and grows to leg spans of 6 inches. A docile new world species found in the Ozarks (southern Missouri), it poses no harm to humans. If provoked to bite, it would only hurt like bee sting. Nobody in history has ever died from a tarantula bite.
Loxosceles reclusa is commonly found throughout Missouri. It's called the "brown recluse" for obvious reasons and most easily recognized by the distinct violin shaped marking on its carapace. Although this spider has received a lot of negative publicity for having necrotic venom that "rots flesh"–bites from this species are very rare. Only 10% of brown recluse bites are medically significant. About 90% heal on their own.
There are multiple species of black widow spiders in the U.S. This spider is regarded as the most venomous spider in North America. Females are easily recognized by their black color, large abdomen, and a red hourglass pattern underneath. They build loose, scraggly webs in sheltered places that look like a tangled ball of yarn. While accidental bites may be very painful and require medical attention, nobody has ever died from a North American black widow.
While they are often demonized and misunderstood, arachnids certainly benefit us in many ways. For instance, they serve a vital role in the environment by consuming a large number of insects they prey on, including a number of pest species. While many people respond with fear at the sight of a spider, understanding that the vast majority of them are harmless and actually beneficial may help us gain a new appreciation for them.
Lund University. 2017. "Spiders Eat More Insects than People Eat Meat and Fish." https://www.lunduniversity.lu.se/article/spiders-eat-more-insects-than-people-eat-meat-and-fish
Missouri Conservation Department. 2018. "Daddy Long Legs (Harvestman)"
National Geographic. 2018. "Black Widow Spider." https://www.nationalgeographic.com/animals/invertebrates/group/black-widow-spiders/?rptregcta=reg_free_np&rptregcampaign=20130916_rw_membership_r1p_w#login/verify
Nyffeler M. and K. Birkhofer. 2017. "An Estimated 400-800 Million Tons of Prey are Annually Killed by the Global Spider Community." The Nature of Science. 104: 30
Sohn, Emily. 2003. "Toxic Spider Species Gets a Bad Rap, Expert Says." National Geographichttps://news.nationalgeographic.com/news/2003/02/0213_030213_brownrecluse.html
Szaley, Jessie. 2014. "Black Widow Spider Facts." Live Science
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REVISED: February 21, 2017