Locust trees are common across many landscapes, found along roadsides, in woodlands, and residential areas. Their widespread presence raises concerns about potential toxicity to humans, pets, and livestock. Understanding these risks is important for safety in environments where they grow.
Understanding Locust Tree Toxicity
Not all trees commonly called “locust” are equally toxic; the primary concern is the Black Locust tree (Robinia pseudoacacia). This species contains poisonous compounds known as toxalbumins, specifically robin and phasin, which are toxic to animals and humans. These toxic proteins disrupt protein synthesis within cells, leading to cell damage and organ system failure. The most toxic parts of the Black Locust tree are its bark, seeds, and leaves. Young shoots and new growth are also highly toxic. While flowers are generally considered less toxic, all parts of the plant are considered poisonous if ingested.
Recognizing Signs of Poisoning
Exposure to toxic parts of the Black Locust tree can cause various symptoms across different species. In humans, common signs include nausea, vomiting, weakness, flushing, and lethargy. More severe, though rare, reports have indicated liver injury and seizures. Gastrointestinal effects typically develop within six hours of ingestion.
Pets such as dogs and cats can exhibit gastrointestinal upset, weakness, depression, and dilated pupils. More severe cases in dogs may involve liver damage, kidney damage, convulsions, and respiratory or cardiovascular issues. Livestock, including horses, cattle, and poultry, are also susceptible. Horses are particularly vulnerable, with symptoms appearing rapidly, sometimes within one to two hours of ingestion. Clinical signs in horses can include depression, lack of appetite, abdominal pain (colic), diarrhea, laminitis, generalized weakness that can progress to paralysis, irregular heartbeat, rapid and shallow respiration, pale mucous membranes, and nervousness. Cattle may show similar signs such as abdominal pain, diarrhea, weakness, depression, and dilated pupils.
Distinguishing Between Locust Tree Species
Differentiating between the highly toxic Black Locust (Robinia pseudoacacia) and the generally non-toxic Honey Locust (Gleditsia triacanthos) is important for safety. Black Locust trees have dark gray, deeply furrowed bark, often with a distinctive mesh-like or X-shaped pattern, and feature stout, paired thorns, usually 5 to 25 millimeters long, at the base of each leaf stalk. Their leaves are pinnately compound, with 11 to 21 oval-shaped leaflets per leaf. The flowers are white, fragrant, pea-like, and grow in drooping clusters. Seed pods are flat, brown, and typically 2 to 4 inches long.
In contrast, Honey Locust trees have smoother bark with less uniform ridges. A defining characteristic is their prominent, often branched thorns, which can be considerably larger, ranging from 3 to 8 inches in length, and sometimes appear in clusters on the trunk and branches. While some Honey Locust varieties are thornless, their leaves are often bipinnately compound, featuring numerous smaller leaflets. The flowers are greenish-yellow and less showy than those of the Black Locust. Their seed pods are large, flat, leathery, and often twisted, reaching lengths of 7 to 18 inches.
Steps to Take After Exposure
Immediate action is necessary if a person, pet, or livestock is suspected of ingesting parts of a Black Locust tree. Contact a poison control center, veterinarian, or medical professional without delay. For human exposures, the Poison Control Center can be reached at 1-800-222-1222. When seeking professional help, be prepared to provide details about the exposure, including which part of the tree was ingested, the estimated quantity, and when the ingestion occurred. Professional medical attention is necessary, and attempting self-treatment is not advised.
Preventative measures are important to avoid such incidents. Educating children about not consuming unknown plant parts is important. For pets, securing them in areas free of Black Locust trees or closely supervising them during outdoor activities can prevent ingestion. In agricultural settings, removing Black Locust trees from grazing areas or fencing them off can protect livestock. Debarking Black Locust wood used for fence posts is also a preventative measure, as the bark contains toxins.