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What Does a Horse Worm Look Like?

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When it comes to caring for horses, one essential aspect that every owner must address is deworming. Worms can cause serious health issues in horses, affecting their digestion, weight, coat condition, and overall well-being. Understanding what horse worms look like is crucial for early detection and effective treatment. This blog post will explore the different types of horse worms and provide insights into their appearance, behavior, and impact on equine health.

Why Deworming is Important

Before delving into the specifics of horse worms, it’s important to highlight the significance of deworming in equine care. Horses are susceptible to various types of internal parasites, commonly referred to as worms. These worms can include large strongyles, small strongyles, roundworms, tapeworms, and bots, among others. When left untreated, these parasites can multiply rapidly within the horse’s digestive system, leading to serious health complications such as colic, weight loss, lethargy, and even organ damage in severe cases.

Regular deworming is essential to control parasite infestations and maintain the health and well-being of horses. Veterinarians typically recommend deworming protocols based on factors such as the horse’s age, environment, and exposure to other horses. Understanding the appearance of horse worms can aid in monitoring infestations and assessing the effectiveness of deworming treatments.

Types of Horse Worms

Large Strongyles (Bloodworms)

Large strongyles, also known as bloodworms, are one of the most common types of internal parasites affecting horses. These worms primarily reside in the large intestine and cecum. They can cause significant damage to the intestinal lining, leading to colic, diarrhea, weight loss, and overall poor health.

Large strongyles are reddish-brown in color and can grow up to several inches in length. They have a distinctive tapered shape, with males typically smaller than females. These worms may be expelled in feces during deworming, especially after treatment with specific dewormers targeting strongyles.

Small Strongyles (Cyathostomins)

Small strongyles, or cyathostomins, are another group of intestinal worms commonly found in horses. Unlike large strongyles, small strongyles can encyst in the intestinal wall in a larval form, making them challenging to eradicate completely. They can cause colic, diarrhea, weight loss, and decreased appetite in affected horses.

The adult form of small strongyles is small, typically less than an inch in length, and can vary in color from white to reddish-brown. Their microscopic larvae, encysted in the intestinal wall, pose a significant threat during certain life cycle stages. Effective deworming strategies often involve targeting both adult and encysted larval stages of small strongyles.

Roundworms (Ascarids)

Roundworms, or ascarids, primarily affect young horses but can also infest adult horses. Foals can acquire roundworm infections from their mothers’ milk or contaminated environments. These worms can cause intestinal blockages, colic, respiratory issues, poor growth, and a pot-bellied appearance in affected horses.

Adult roundworms are large and white, resembling spaghetti strands, and can grow several inches in length. Their eggs are passed in feces and can survive in the environment for extended periods, posing a risk of reinfection. Deworming programs for foals often target roundworms to prevent serious health complications.


Tapeworms are flat, segmented parasites that attach themselves to the walls of the horse’s intestines, particularly the ileocecal junction. They can cause colic, weight loss, and digestive disturbances in horses. Tapeworm infestations are commonly diagnosed through fecal egg counts and specialized diagnostic tests.

The segments of tapeworms, known as proglottids, can sometimes be visible in the horse’s feces or around the anal area. These segments resemble small white or yellowish rice grains and can be a sign of tapeworm infestation. Effective deworming protocols often include specific medications targeting tapeworms in addition to other parasites.


Bots are the larvae of bot flies and can infest horses’ stomachs and intestines. Adult bot flies lay their eggs on the horse’s hair coat, and when horses groom themselves, they ingest these eggs, leading to bot infestations. Bots can cause irritation, ulcers, and digestive disturbances in horses.

Bot larvae are yellowish-white and can be found attached to the stomach lining or passed in feces. They have a distinctive appearance, often resembling small maggots or grubs. Deworming programs targeting bots typically include medications effective against bot larvae at specific life cycle stages.

Recognizing Horse Worms

While some horse worms, like roundworms and bots, may be visible to the naked eye, others require microscopic examination for accurate identification. Veterinarians often rely on fecal egg counts and diagnostic tests to assess parasite burdens and tailor deworming protocols accordingly.

Here are some general guidelines for recognizing horse worms:

  1. Visible Worms: Roundworms and bot larvae may be visible in feces or around the horse’s anal area, especially during and after deworming treatments.
  2. Diagnostic Tests: Fecal egg counts and fecal flotation tests can detect eggs or larvae of various worm species, aiding in targeted deworming strategies.
  3. Clinical Signs: Monitor horses for symptoms such as colic, diarrhea, weight loss, poor coat condition, and changes in appetite, which can indicate worm infestations.
  4. Veterinary Guidance: Consult your veterinarian for regular fecal testing, deworming schedules, and appropriate medications based on your horse’s age, health status, and environmental factors.

Deworming Best Practices

Effective deworming programs encompass more than just administering dewormers at regular intervals. It involves strategic planning, fecal testing, pasture management, and proper hygiene practices. Here are some best practices for deworming horses:

  1. Fecal Testing: Perform regular fecal egg counts to assess parasite burdens and determine the most appropriate deworming medications.
  2. Targeted Deworming: Tailor deworming protocols based on fecal test results, age, health status, and risk factors for individual horses.
  3. Pasture Management: Practice rotational grazing, remove manure regularly, and minimize overcrowding to reduce parasite exposure in pastures.
  4. Quarantine and Hygiene: Quarantine new horses before introducing them to resident horses, practice good manure management, and maintain clean feeding and watering areas.
  5. Follow-up Monitoring: Monitor horses post-deworming for any signs of reinfection or adverse reactions to medications.

By adopting these practices, horse owners can contribute to healthier herds, reduce parasite resistance to dewormers, and promote overall equine well-being.


Understanding what horse worms look like and their impact on equine health is crucial for effective deworming and parasite control. From large strongyles to tapeworms and bots, each parasite presents unique challenges and requires targeted deworming strategies. Regular fecal testing, veterinary guidance, pasture management, and hygiene practices play key roles in maintaining horses’ health and minimizing parasite burdens. By staying informed and proactive, horse owners can ensure the well-being and longevity of their equine companions. Remember, a healthy horse is a happy horse!

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