The poison hemlock is native to northern Europe, western Asia, and North Africa, where it grows in woodlands, grasslands, wastelands, and disturbed ground. The species has been introduced to North and South America, Australia, and New Zealand, as well as to non-native parts of Asia and Africa. It is listed as a noxious weed in many US states and as invasive in New Zealand and parts of Australia.

Ingestion of poison hemlock severely poisons dogs, cats, and humans, affecting the nervous system. Symptoms appear within an hour, including muscle pain, loss of speech, and sometimes unconsciousness. Severe cases can cause kidney or respiratory failure and death. Often mistaken for wild parsnip, poison hemlock contains alkaloids causing vomiting, seizures, and paralysis. Immediate veterinary care is critical for pets.

Native across Eurasia and North Africa, poison hemlock has spread around the world and is invasive in Australia, New Zealand, Mexico, Costa Rica, Ecuador, Peru, and Chile. Not only is it highly invasive, it is also a serious health hazard due to its high level of toxicity. Every part of the plant is poisonous, and even the dead canes remain toxic for up to three years. They pose a risk to humans and animals alike. Symptoms include dizziness, trembling, slow heartbeat, muscle paralysis, lack of coordination, and can possibly lead to death. Ingestion is the most dangerous, but skin contact can also cause reactions and irritation. Take care to use gloves and protective clothing during removal.

The best season to remove poison hemlock is during spring and fall. Ideally, it's important to get rid of poison hemlock before it blooms and produces seeds to prevent further infestation.