Milkweed, commonly known for its rough, funny-looking fruit pods filled with white, silky floss, grows abundantly throughout the lower 48 states and Hawaii. The floss, wax-covered and naturally buoyant, was used in Army life preservers during World War II. Today, common milkweed, or Asclepia syriaca, is cultivated commercially to fill comforters and pillows. While milkweed is the favorite food of monarch butterfly larvae, most animals find it unpalatable and for some, including your pooch, potentially deadly.
The Heart Does Not Want What the Toad and Milkweed Have
All species of milkweed can be poisonous to a degree, but some more so than others. Generally, narrow-leaved species are more toxic than broad-leaved varieties. The primary toxic agent appears to be cardenolides, a group of cardiac glycosides that interfere with electrolyte balance in the heart. Oleander plants and the venom of cane toads both contain cardiac glycosides. Galitoxin and other resins found in milkweed’s creamy sap may add to the plant's toxicity. All above-ground parts of the plant are poisonous, particularly during rapid growth, and remain so even when dried. Symptoms of poisoning often begin with gastrointestinal signs -- excessive drooling, vomiting, nausea and diarrhea -- and progress to heart and central nervous problems, which may include an abnormal heart rate or rhythm, dilated pupils, tremors, seizures and even death. If you suspect your pooch has gobbled up some milkweed, immediately contact your veterinarian or call one of the pet poison hotlines. In most cases, Fido will be back to his old self with veterinary intervention and supportive care. In severe cases, your vet can administer an effective, but expensive, antidote called digoxin-specific antibody fragments.
Once Eaten, Twice Shy
Milkweed poisoning in dogs and cats is thankfully rare, unless your pet is prone to dining on terribly bitter tasting greenery. Incidents are more common in bona fide grazing animals such as horses, cattle and, more often, sheep. While milkweed can be poisonous to many species, some have turned this toxicity to their strategic advantage. The unforgettable monarch butterfly relies exclusively on milkweed as its larval food source or host plant. Monarch moms lay a single egg underneath a milkweed leaf. Four to seven days later, the monarch caterpillar hatches and begins voraciously feeding on leaves, all the while taking on the plant's bitter taste and its toxic properties. Just one run-in with a milkweed-marinated caterpillar convinces a bird to avoid eating monarchs, as well as the butterfly species that mimic their color and pattern.
- USDA Natural Resources Conservation Service: Plants Database: Asclepias L. Milkweed
- Pantagraph: Kids Gathered Milkweed Pods for WWII Effort
- USDA: Agricultural Research Service: Milkweed
- ASPCA: Animal Poison Control: Milkweed
- American Board of Veterinary Toxicologists: A Review of Veterinary Antidotes
- DVM360: Toxic Plants (Proceedings)
- Monarch Butterfly Fund: The Monarch Butterfly's Annual Cycle
Barbara Cozzens has been writing for more than 20 years. Her work has appeared in publications of the Nature Conservancy, the World Bank Group, National Geographic Society, Duke University and others. Cozzens holds a Bachelor of Arts in biology from Colgate University and a Master of Environmental Management from Duke University's Nicholas School of the Environment.