Mysterious Red Widow Spider's Diet Revealed

Red widow spiders in Florida feast on scarab beetles native to their habitat, according to a new study that offers the first insights into the diet of the mysterious spider.

University of Missouri biologist James Carrel and his colleagues made the discovery while studying the spider in its native pine scrub habitat, learning that the red widow prefers to eat scarab beetles common to the ecosystem.

"The pine scrub habitat, found on sandy ridges in Central and Southeastern Florida, is one of the oldest in North America," Carrel said in a statement. "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."

The reddish-orange coloring of its head, carapace, and legs give the red widow (Latrodectus bishopi) its name. The spider is venomous, but there have been no recorded instances of it biting a human.

The behavior patterns of the red widow have remained elusive for biologists because of their confinement to such a specific habitat and because they tend to hide their webs in palmetto shrubs. The spiders conceal their funnel-shaped webs in the shrub's unopened leaves, making them difficult to spot. The spider is so elusive that it's only really visible on foggy mornings four months out of the year, when the thin threads the spider spins between palmetto leaves are visible.

Carrel's study of the red widow dates back to 1987, when he began monitoring populations of the spider at the Archbold Biological Station, which protects a 5,193-acre Florida scrub preserve near Lake Placid.

Only twice in the 23 years since he began studying the red widow - in March 1989 and May 2003 - have enough webs been located to study the dietary habits of the red widow.

Carrell and his collaborator Mark Deyrup, senior research biologist for the Archbold Biological Station, have ascertained that the red widow feeds on at least five species of scarab beetle that are endemic to its habitat.

"The scarab beetles, which often are larger and stronger than the spiders themselves, fly just above the tops of scrub vegetation," study co-author Deyrup said. "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 biologists published the details of their study in the journal Florida Entomologist.