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Nature Notebook – Bolas Spiders

After researching cecropia moths last week (the largest moth species in North America) I came upon an interesting predator of them – bolas spiders.

These orb-weaving spiders in the genus Mastophora, of which there are 13 species in the continental United States,do something unique to catch their prey. They use their silk webbing and dispense a single line, attaching it to a plant. They then act as tiny fishermen, and with great accuracy and skill, use this line as a lasso and swing it at passing insects.

At the end of the line is a sticky ball that if thrown correctly, entangles the insect prey and allows the spider to pull in the line and inject their venom, subduing the victim quickly.

Another amazing hunting technique bolas spiders have evolved to use is the ability to mimic insect pheromones. That sticky ball at the end of the lasso is covered in not only the coiled silk and glue made by the spider, but also pheromones. Male moths are attracted to the pheromone thinking it is a female moth, approach from downwind and are lured into the trap. Immature and thus smaller bolas spider use a pheromone to attract male psychodid flies.

To deter their own predators when resting, these tiny 1/16th to 1/2-inch adults resemble bird droppings.