The question “do blackjacks sting?” often arises from encounters with this widespread plant. Blackjacks, scientifically known as Bidens pilosa, do not possess a stinging mechanism like an insect. They do not inject venom or any irritating substance. This article explains the plant’s characteristics and the actual cause of the sensation many people associate with a “sting” from this common weed.
Understanding “Blackjacks”
The plant commonly referred to as “blackjacks” is Bidens pilosa, an annual herbaceous flowering plant in the daisy family Asteraceae. It is also known by various other names, including beggarticks, cobbler’s pegs, and Spanish needle. This plant can grow up to 1.8 meters tall and features small, often white or yellow flowers at the ends of its stalks.
The most distinctive characteristic of Bidens pilosa is its seeds, which are responsible for its common name. These seeds are elongated, stiff, rough, black rods, typically about 1 centimeter long, equipped with two to three stiff, heavily barbed awns at one end. Native to the Americas, this plant has become widely naturalized across tropical and warm temperate regions globally, thriving in disturbed land.
The “Sting” Clarified
The sensation described as a “sting” from blackjacks is not biological, but rather a purely mechanical interaction. The unique structure of the Bidens pilosa seeds is responsible for this perception. Each seed possesses specialized barbed awns at its tip. These awns are designed to easily catch onto surfaces.
When a person or animal brushes against the Bidens pilosa plant, these barbed awns physically snag onto clothing, animal fur, or skin. This adhesion is an effective method of seed dispersal. The sensation of a “prick” or “snag” occurs as the seeds’ barbs make contact and attempt to embed themselves. Unlike an insect sting or contact with a stinging nettle, this sensation does not involve the injection of irritants or venom.
Dealing with Blackjack Seeds
Encountering blackjack seeds on clothing or skin is common due to their effective attachment mechanism. For removal from clothing, methods such as brushing them off vigorously, using sticky tape, or employing a fine-toothed comb are effective. If seeds are caught in hair, a comb is typically the most efficient tool.
When seeds attach to the skin, they can cause a minor, temporary sensation of itching or mild redness due to the physical pricking action. These reactions are not severe and subside quickly once the seeds are removed. To prevent attachment, wearing long pants and sleeves, especially when walking through areas known to have blackjacks, significantly reduces direct contact. Regularly checking clothing and skin after being in such environments helps in early detection and easy removal.