Which spider uses a sticky ball on a thread to catch moths?

The bolas spider uses a sticky ball on a silk thread to catch moths. Instead of building a conventional orb web, an adult female suspends a single thread with one or more glue-like droplets at its end and swings it at passing prey.

The spider first attracts male moths by releasing chemical signals that imitate female moth pheromones. When a moth approaches, the spider detects its wingbeats and sweeps the bolas through the air, snagging the moth on the sticky droplet. The technique is especially effective because moth wing scales can detach when they contact ordinary spider silk.

Bolas spiders belong to the orb-weaver family Araneidae, even though adult females do not use typical orb webs. Several related genera perform the behavior, including Mastophora in the Americas and Ordgarius in Australia and parts of Asia. Some species also disguise themselves as bird droppings or other objects during the day.

A common mix-up is calling every fishing spider a bolas spider. The name “fishing spider” is also used for unrelated Dolomedes spiders, which hunt near water rather than swinging a sticky silk ball at moths.