It’s no wonder that many of us two-leggers get the heebie-jeebies at the sight of spiders.
With their far-too-many legs, shiny or furry bodies — often painted with cryptic symbols — and mechanical, creeping movements, they seem alien next to soft, clumsy human bodies.
At Halloween time, decorative spiders and webs adorn homes, reminding people of their tendency to live in dark, abandoned places.
The jitters humans feel are real, but quite unfair.
“Spiders are a source of phobia, but aren't generally aggressive or looking to bite people,” said Michael Skvarla, Ph.D., insect identifier and Extension Educator, Department of Entomology, Penn State University. “They just want to go about their business eating insects. If you don't bother them they won't bother you.”
Not only do spiders rarely cause harm, they contribute pest control services, keeping other creepy-crawlies from eating crops and spreading disease.
“Spiders are the most important predators in a number of crops, so provide direct benefits to people by reducing the number of insect pests and subsequent need for pesticide use in crops,” said Skvarla. “It's difficult to put solid numbers to them, but spiders easily provide hundreds of millions of dollars worth of benefit to farmers every year.
“Spiders also eat non-crop pests such as mosquitoes and flies outdoors, and cockroaches, silverfish, and termites indoors, which can, for example, help limit disease transmission,” he said.
Skvarla doesn’t know how many species of spiders are in Pennsylvania; to his knowledge, no one has counted.
But he did say, “There are around 3,700 named species of spider in North America, plus a few hundred to few thousand undescribed species.”
A Penn State fact sheet on spiders provided by Skvarla talks about some types commonly found in Pennsylvania: funnel weavers, hacklemesh weavers, a variety of orbweavers, broad-faced sac, woodhouse hunters, parson, wolf, prowling, fishing, cellar or daddy longlegs, jumping, brown recluse and cobweb weavers (which include southern black widow, common house and false black widow spiders).
When asked about the most dangerous spiders in Pennsylvania, Skvarla’s answer offered a new perspective.
“I wouldn't say dangerous as issues with spiders almost always happen because people mistreat or mishandle them,” he said.
Spiders bite out of self-defense, not aggression.
“That being said, the two most medically important species in the state are black widows and brown recluse,” he added.
Many people experience little or no reaction to bites from black widows or brown recluses, but the possibility of serious symptoms or even death gives these arachnids a bad reputation.
In fact, “unless someone is bitten by a black widow or brown recluse and has a bad reaction, medical attention is not generally warranted for a spider bite,” said Skvarla.
He noted that he is not a physician and cannot give medical advice.
Regarding black widows, Skvarla explained the spider is “native and widespread throughout Pennsylvania, but rarely encountered.”
He indicated that is because the spider does not approach people.
“Black widows are generally calm spiders and most bites occur when someone accidentally grabs one they don't see, such as picking up split wood or putting on a boot or glove where a spider is hiding,” he said.
When bitten, the reactions vary from almost no reaction, to more severe and rarely fatal — usually in the very young and old.
While he wasn’t sure when the last person died of a black widow bite in the United States, it happens very rarely and has perhaps been decades since the last fatality.
Someone who experiences only a little pain needs no special treatment.
“Other times, there is immediate pain around the bite and the muscles around the bite start to cramp,” Skvarla said. “The pain and muscle cramps can spread to the center of the body, which can be extremely painful and mistaken for a heart attack or appendicitis. Treatment in such cases usually consists of painkillers and muscle relaxants until the cramping subsides, sometimes over a few days.”
The antivenin for black widow bites “is used only in the most extreme cases as there is a risk of an allergic reaction to the antivenin that is worse than the bite itself.”
Meanwhile, brown recluse spiders are not found in Pennsylvania naturally and are hardly ever spotted here.
“Every case in the state has involved someone who moved from where brown recluse are native and brought the spiders with them,” he said. “When brown recluse are found, they're always restricted to the house they infest as they don't survive outdoors.”
Skvarla referred to multiple studies that show brown recluse bites are overdiagnosed and are often medical issues such as poison ivy, chemical burns and diabetic ulcers — not bites at all.
Even in homes in the spider’s native range where brown recluses are abundant, bites are rarely reported, he added.
Similar to black widow bites, “When (brown recluse) bites do occur, it is usually because a spider is trapped against the skin and feels threatened, such as when someone puts on shoes that were left on the overnight or roll over a spider while sleeping,” he said.
According to Skvarla, the large necrotic lesions people associate with brown recluse bites are rare. About 10 percent of bites result in dermonecrotic lesions; the rest have no reaction or cause a small red papule that heals on its own.
The dermonecrotic lesions “develop over the course of two weeks, in which time the flesh and skin surrounding the bite turns black, dry, and eventually sloughs off,” he said. “These bites take two to four months to fully heal.”
He said less than 1 percent of brown recluse bites cause potentially fatal systemic symptoms such as hemolytic anemia and acute kidney injury.
“These symptoms are most common in children and can be fatal in 12-36 hours, so represent a true medical emergency,” Skvarla added.
He recommended monitoring all brown recluse bites.
Skvarla was asked if there were any types of spider he found particularly interesting.
His answer? Bola spiders.
While other orbweaving spiders spin webs, bola spiders don’t.
They use trickery to bring in their food of choice: male moths.
He explained, “Bola spiders attract male moths by mimicking the pheromones of a female moth, then swinging a strand of web with a sticky ball at the end at the moths to catch them. When a moth is ensnared, the bola spider reels it in.”