Are black locust trees toxic?
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The bottom line
The bark, seeds, and leaves of black locust trees contain poisonous compounds called toxalbumins. They are toxic to both livestock and humans and can cause symptoms ranging from stomach upset to nervous system problems.
Prevention tips
Have a knowledgeable expert identify the plants and trees growing in your home, backyard, and neighborhood, so you know which are harmful and which are safe around children and pets.
Call your local plant nursery to see if they can help you identify samples of plants.
Never eat an unknown plant or seed without verification from a clear field guide or someone with experience.
If you are interested in foraging for wild plants, join an organization with experienced members.
Always wear appropriate protective gear like gloves when gardening and pruning.
Consult our plant guide for more tips.
This really happened
An 8-year-old boy developed symptoms 2.5 hours after chewing a piece of locust bark the size of an adult hand (3–4 mouthfuls). He vomited 5 times before being seen in an emergency department. Lab tests were normal except for a high white blood cell count and a raised liver enzyme, which peaked on day 5. He was treated with ondansetron (an antinausea medication), activated charcoal, and IV fluids. He was sent home on day 5 with a normal white blood cell count (from Hui et al., 2004).
What are black locust trees? Where are they found?
The black locust (Robinia pseudoacacia) tree is native to the eastern and central US. Generally blooming in May or June, the white flowers of the tree droop into clusters about 4–8 inches long.
Another characteristic feature of the black locust tree is the light- to dark-brown legumes (pods) that are found on the tree during the winter. They are usually about 2–4 inches long, flat, straight or slightly curved, and typically contain 3–10 seeds per pod. Young saplings and new growth have sharp thorns up to ½ inch in length.
Are black locust trees toxic?
Black locust trees contain the toxalbumins (toxic protein molecules) robin and phasin in their leaves, bark, and seeds. These compounds block cells from making protein, which can kill the cells. The flowers appear to be nontoxic or substantially less toxic.
The earliest reports of possible poisoning associated with the black locust involved livestock, which either became severely ill or died from swallowing parts of the tree. There have also been a handful of cases in which young children have become sick after chewing on or eating parts of the bark or seeds.
What to do after a black locust tree exposure
All black locust exposures should be taken seriously. If someone eats part of a black locust tree or is pricked by its thorns, use the webPOISONCONTROL® online tool to get help, or call your poison center at 1-800-222-1222. Whether online or by phone, expert guidance is always free, confidential, and available 24 hours a day.
Symptoms of black locust poisoning
The most common symptoms after ingestion include nausea, weakness, flushing, lethargy, and vomiting. Symptoms appear to be related to how much was swallowed and how much it was chewed. Larger amounts and more chewing can lead to dilated pupils, a weak or irregular pulse, fever, fast heart rate, fast breathing, agitation and seizures. As the amount ingested increases, paralysis and coma may occur. Gastrointestinal bleeding and liver and kidney damage may also occur. Most stomach and gut symptoms develop within 6 hours and can lead to complications such as dehydration.
Dangers to the skin
The thorns can puncture the skin. Most of these injuries cause only local symptoms such as pain, swelling, and rash. A few reports describe more severe outcomes following punctures from black locust thorns, including neurologic (brain-related) symptoms and local tissue death (necrosis).
For more info
References
Bou XC, Soler JM, Ros SI, Seculi-Palacios JL. Intoxicacio´n por Robinia pseudoacacia. An Esp Pediatr. 1990;32:68–9.
Burrows GE, Tyrl RJ. Toxic Plants of North America. 2nd ed. Wiley-Blackwell; 2013: 595-597.
Filandrinos DT, Sioris LJ. Transient elevation of liver function tests following ingestion of black locust seeds [abstract]. Vet Hum Toxicol. 1992;34(4):351.