Spiders: the allure and fear of our eight-legged friends
Environmental Entomology is published bimonthly in February, April, June, August, October, and December. The journal publishes reports on the interaction of insects with the biological, chemical, and physical aspects of their environment.
What’s your first reaction when you see this picture? Love? Fear? Repulsion? If you are like many Americans, when you come across a spider, especially a large, hairy one like this tarantula, the emotions you experience are most likely in the realm of fear or disgust. Your actions probably include screaming, trapping, swatting, or squashing of the spider.
Despite their negative reputation, spiders are essential members of the global ecosystem. They are present in all terrestrial habitats, except Antarctica, and thrive wherever insect prey and vegetation are present, including freshwater ponds, caves, agricultural crops, and to elevations over 20,000 feet ¬- over 40,000 spider species worldwide. The thing that many people fear about spiders – the predatory instinct – is exactly what makes spiders beneficial. They feed on a variety of insect and invertebrate prey that humans consider pests.
Spiders are beneficial to humans beyond their role in controlling pests. The silk and venom of spiders has commercial appeal. Due to the strength and elasticity of spider silk, it is being considered for mass production for gloves, bullet-proof vests, parachutes, and cables. A peptide from tarantula venom was found that inhibits atrial fibrillation in rabbit hearts, which may be beneficial for the prevention of arrhythmia in humans.
The more we understand these eight-legged creatures, the less we will fear them. With only a few species considered harmful to humans and their tendency to avoid human encounters and bites, their negative reputation is unjustified.
In honor of “Save a Spider Day” take a look at these fascinating species and marvel at the unique biology and adaptations of the arachnid world.
Cat-faced spider, Araneus gemmoides
In your gardens, these eight-legged hunters will help control the troublesome aphids and spider mites. The cat-faced spider, Araneus gemmoides, will build large spiral orb webs on porches, catching the pesky moths, flies, and mosquitoes that are attracted to lights. They are not the go-to predators for specific pest control outbreaks because of their tendency to feed on a variety of prey. Image credit: Photo by Whitney Cranshaw. Used with permission.
Long-jawed orb-weaving spider, Tetragnatha laboriosa in wheat
But the presence of spiders, like the delicate-looking long-jawed orb weaver, which feeds on aphids and other wheat insect pests, is critical in keeping pest populations below damaging levels. Image credit: Photo by Laurie Kerzicnik. Used with permission.
Funnel web spider
Most of us associate spiders with webs, but not all spiders build webs. Web builders include funnel web weavers, tangle web weavers, orb weavers, and sheet web weavers. Image credit: Photo by Whitney Cranshaw. Used with permission
Crab spider, Bassiana sp.
Other spiders are considered hunters, ambushers, or burrowers. Hunting spiders don’t use webs or silk to catch their prey. Instead, they chase down and grasp their prey. These include ground spiders, wolf spiders, ant mimics, and sac spiders. Jumping spiders and crab spiders are ambushers. Some crab spiders will await the arrival of large bees and other pollinators two to three times their size within flowers, with their crab-like legs outstretched. When the pollinator arrives, they will snatch it with their extended legs and inject venom. Some of the burrowers include tarantulas and trap door spiders, and they capture prey by hunting and seizing it. Image credit: Photo by Whitney Cranshaw. Used with permission.
Yellow sac spider, Cheiracanthium sp.
Spiders are timid and would likely try to escape rather than bite. Biting a human is a waste of venom and depletes one of their only resources for prey capture. Venom is used to subdue or immobilize insect or invertebrate prey. After injecting it, a digestive enzyme is regurgitated onto the immobilized prey, creating a liquid meal that will then be sucked back up by the spider. Image credit: Photo by Whitney Cranshaw. Used with permission.
Although spiders have eyes, their vision is mainly targeted for sensing movement. They rely on sensory structures such as chemical receptors and fine hairs. The chemical receptors are similar to “taste” hairs when they come into contact with a substrate. The fine hairs are critical for sensing motion, air currents, and vibrations. Image credit: Photo by Alex Stephens. Used with permission.
The Brown Recluse Spider
In spite of their bad reputation, only about 100 species worldwide are of medical concern to humans. In the United States, there are only three spiders (five spider species) that can cause real harm to humans: black widows (Latrodectus hesperus, Latrodectus mactans, and Latrodectus variolus), a brown widow (Latrodectus geometricus), and the brown recluse (Loxosceles reclusa). Image credit: Photo by Laurie Kerzicnik. Used with permission.
Unfortunately, spiders often take the blame for any sort of lesion or bite that appears on someone’s body, when, in fact, most of the smaller spiders that are commonly encountered can’t even pierce human skin with their fangs. In the midst of spider hysteria, it’s important to remember that almost all spider bites involving humans are nonthreatening. A spider bite and its associated symptoms are often based solely on anecdotal evidence without a spider being captured or professionally identified. Sometimes a specific species, like the brown recluse, Loxosceles reclusa, is accused of biting someone in a location that is not even part of its native range. Many times the victims of “spider bites” do not witness the bite and sometimes they never saw a spider at all! For years, spider bites have been chronically over diagnosed. These misdiagnoses could, in actuality, be infections (bacterial, fungal, or viral), allergic reactions, other arthropod bites, or many other serious medically-related conditions.
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