According to a study by University of Missouri biologist James Carrel, the diet of the mysterious red widow spider (Latrodectus bishopi Kaston) consists mainly of five species of scarab beetles that are endemic to the Florida scrub habitat, which limits the range of the spiders.
“The pine scrub habitat, found on sandy ridges in Central and Southeastern Florida, is one of the oldest in North America,” said Carrel. “Many of the plants and animals found on these ridges, including the red widow spider, are restricted to these high, dry areas. Our research suggests that red widows have evolved to specialize on scarab beetles because they are reliable food sources.”
Red widow spiders are difficult to study due to habitat confinement and the hidden nature of their webs, which are built in palmetto shrubs. Red widows conceal their funnel-shaped retreats in unopened palmetto leaves, making them difficult to spot. The only clues to the spiders’ presence, visible solely on foggy mornings during four months of the year, are the threads spun loosely between tips of palmetto frond.
Since 1987, Carrel has been monitoring populations of this spider at the Archbold Biological Station, which protects a 5,193-acre Florida scrub preserve near Lake Placid. Only twice in those 23 years — in March 1989, and in May 2003 — have enough webs been located to study the dietary habits of these elusive spiders. The scientists identified 43 species of insects among the 98 specimens collected. The study revealed that the primary prey of the spider, especially in early spring, are five species of scarab beetles endemic to the area.
“The scarab beetles, which often are larger and stronger than the spiders themselves, fly just above the tops of scrub vegetation,” said Mark Deyrup, senior research biologist for the Archbold Biological Station, who co-authored the study. “Sometimes beetles hit the web strands between tips of palmetto fronds and tumble into the denser tangle of threads below, catching them in the red widows’ webs.”
The research appears in the March issue of the Florida Entomologist.
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