Bidens pilosa, commonly known as Spanish needle or beggar’s ticks, is a fast-growing annual herb native to the Americas but now widespread across tropical and subtropical regions worldwide. It has upright, branching stems, paired toothed leaves, and small daisy-like flowers with yellow centers and occasional white rays. The plant is easily recognized by its slender, barbed seeds that cling to clothing and animal fur. Though mostly considered a weed, Bidens pilosa has a long history of use in traditional medicine and is sometimes utilized as a leafy green or forage plant in parts of the world.

In Hawai‘i, Spanish needle is considered an invasive weed. It grows quickly, spreads aggressively, and thrives in disturbed areas, roadsides, pastures, and agricultural lands. Its sticky seeds disperse readily on people, animals, and equipment, helping it move into new areas with ease. Spanish needle can form dense patches that outcompete native plants and hinder pasture and crop productivity. While it is not typically a threat to intact native forests, it is a persistent nuisance species that is difficult to control once established.