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TAMPA, Fla. (Feb. 26, 2026) – A newly published study co-authored by University of South Florida alum Louis Coticchio and USF integrative biologist Deby Cassill challenges long-standing assumptions about the brown recluse spider, finding the species is both far less common in Florida and far less aggressive than public perception suggests.
The findings, published in the Journal of Medical Entomology , aim to change the narrative by debunking common myths of this misunderstood arachnid.
Chills run down many people’s spines at the mere mention of a spider. However, according to Coticchio, spiders, especially the brown recluse, shouldn’t be portrayed as villains.
“This research shows that brown recluse spiders aren’t the boogeyman that everyone makes them out to be,” Coticchio said. “They aren’t swarming throughout Florida, infiltrating homes and attacking. Rather, they are misunderstood and want to be left alone while rarely showing signs of aggression, even when provoked.”
The researchers systematically evaluated three questions central to the spider’s reputation: geographic prevalence in Florida, likelihood of biting when provoked and severity of resulting wounds.
The brown recluse ( Loxosceles reclusa ) is native primarily to the Midwest and parts of the Gulf Coast and is not endemic to Florida. To assess its presence in the state, the study investigated 220 Florida properties that had reported suspected infestations.
Breeding populations of invasive Mediterranean recluse spiders were found at only 19 sites, concentrated mainly in central and north Florida. Population sizes ranged from a single specimen to 171 individuals at a given property.
The findings suggest that established populations remain localized rather than widespread, countering frequent claims of statewide infestation.
Reluctant to bite, even when provoked
To test defensive behavior, Coticchio conducted controlled laboratory trials applying standardized, incremental pressure stimuli using gel-tipped instruments. He recorded bite frequency and compared the responses to wolf spiders tested under identical conditions.
Wolf spiders bit in approximately 80% of trials when provoked, while brown recluse spiders bit primarily when subjected to extreme stress — such as being squeezed or inverted. Under milder provocation, bites were infrequent.
The data indicate that recluse spiders exhibit a markedly lower propensity to bite than commonly assumed.
Necrosis typically superficial
The study also examined one of the most feared outcomes of a bite: necrosis, or tissue death. Coticchio found that when bites occur, they typically produce shallow wounds about half a centimeter deep. In rare cases, necrosis can develop, but it is usually limited to the skin's surface layers and does not extend into muscle or bone.
Most verified bites result only in redness, burning or small blisters that heal over time. Severe wounds often attributed to recluse spiders are more likely caused by bacterial infections, such as staph.
Implications for medicine and public health
The published findings lay a foundation for educating both the public and the scientific community. Coticchio plans to continue investigating a mystery population of Mediterranean recluse spiders discovered in St. Augustine.
He hopes to determine whether the group originated from a single introduction event or multiple arrivals over time, which could reveal how its population might grow.
“The research community has been very open to our study,” Coticchio said. “We sensed there was an urgency to get this study out there and prove the narrative toward the brown recluse has been overblown. I'm not saying that they're completely harmless, but rather they’re reluctant to bite, and there’s an extremely low percentage of encountering them in Florida.”
Behind the research
Long before Coticchio became a spider expert, he had a childhood fascination with the outdoors.
“Growing up in Largo (Florida), I was catching and keeping everything I could find while playing outside,” Coticchio said. “I would bring in rattlesnakes, alligators, you name it. Though they would frighten my mother, it sparked my early interest in biology.”
He continued that passion as an undergraduate biology student on the USF St. Petersburg campus. Coticchio focused on the brown recluse starting in 2019 when he joined Cassill’s lab and launched the Florida Brown Recluse Spider Project to further education and research on the topic.
“Lou is the gift of a century, and every research professor needs one brilliant student like him,” Cassill said. “He walked into my office as a freshman as a self-guided person with a great work ethic and a passion for changing how we think about spiders. I felt very fortunate to play a part in this research led by him; he's the real Spider-Man.”
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Journal of Medical Entomology
Experimental study
Animals
Recluse spiders (Araneae: Sicariidae): contesting myths on distribution, bite behavior, and medical risk in Florida
6-Feb-2026