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Caring for horses is a wonderful activity as you get to enjoy plenty of fresh air, exercise, and time in nature. However, this also means you come into contact with pests that you need to know how to deal with.
Bot flies are one of these pests. These common parasites can infect horses and cause a range of unwanted health effects. Like stable flies, horse flies, ticks, and mosquitoes, they are classified as ectoparasites, a type of parasite that lives and feeds on the surface of an animal’s skin.
In the UK, the horse bot fly is a relatively large insect resembling a wasp or hornet. These slim, bristly brown-and-yellow flies buzz around a horse’s head, body, and lower legs as they attach their eggs to the horse’s coat.
To help you keep your horse happy and healthy, we’ve shared our extensive knowledge about the botfly and how to prevent and treat it.
The Life Cycle of the Horse Bot Fly
Bot flies have a unique life cycle with a few distinct stages. The first stage of their life cycle occurs at the start of summer when adult flies lay their eggs on horses during their seven to ten-day lifespan. These eggs resemble small yellow or yellowish-grey dots, around 0.12cm in length, which are individually attached to a horse’s hair.
Hatching, Migration, and Feeding
After the larvae inside the eggs have incubated, they hatch and migrate to a horse’s stomach. Once they have entered the stomach, botfly larvae will attach themselves to the stomach walls and feed, growing as they do.
The larvae feed by burrowing their powerful mouth hooks into the tissue of a horse’s stomach and attaching themselves to non-glandular parts of the stomach lining.
Emerging, Mating, and Egg Laying
The maggots will then feed from the horse for the next eight to ten months, typically between late autumn or early winter and the start of the following spring. Once spring arrives, the larvae are passed from the stomach when the horse defecates. They pupate on the ground, emerging as adult bot flies around a month later.
Once they emerge, they quickly mate during warm and sunny days, and the female will set off to find another equine host on which to lay her eggs. Most females will lay their eggs on as many horses as they encounter, maximising the chances of their larvae surviving another life cycle.
Identifying Different Botfly UK Species
Interestingly, there are two different varieties of botfly in the UK: Gasterophilus nasalis and Gasterophilus intestinalis.
Each G. intestinalis adult fly can lay up to a thousand eggs, primarily on a horse’s shoulders and legs. These eggs are pale yellow in colour, and will hatch after about seven days after laying. Once hatched, the larvae will enter the horse’s mouth as it grooms itself and migrate to the stomach.
G. nasalis adults lay a few hundred eggs each around a horse’s throat, neck, and chin areas. These eggs don’t require moisture from a horse’s tongue in order to hatch. The larvae of this species burrow under the horse’s skin to the mouth, where they stay for around a month before moving to its stomach during the winter.
How Botfly Affects Horses
Botfly infestations can have notable health impacts on horses. Affected horses may present with a dry and lacklustre coat, a lack of appetite, and a fever. They may also kick at their bellies, indicating discomfort, seem restless and persistently uncomfortable, and display general poor health and condition.
Some horses also present with alternating bouts of constipation and diarrhoea. This is because botfly larvae can cause gastrointestinal issues such as stomach ulcers and gastritis. In rare cases, they can even perforate the lining of a horse’s stomach, which could lead to fatal peritonitis.
Best Practices for Botfly Prevention
Preventing botfly infestations is the best way to protect your horse against this potentially dangerous parasite. Start by using our Bitz Bot Knife to remove botfly eggs from your horse’s coat daily and keep your stables and fields clean and free from manure, as this is where the flies emerge to continue their life cycles.
It’s also a good idea to de-worm your horses regularly with an appropriate de-worming agent. Consider turning your horses out in one of our high quality turnout rugs after sunset and bringing them back in at dawn, too; bot flies are usually most active around late afternoon and will be less likely to be able to lay their eggs if your horses are stabled at this time.
Many horse owners use a fly spray containing active ingredients like permethrin or cypermethrin to control the flies and prevent them from laying their eggs. Our fly rugs and sheets, fly veils, and fly masks can also create physical barriers that prevent the flies from being able to lay eggs on the horse’s hair and skin.
Botfly Treatments for Horses
Treating botfly infestations requires a strategic approach based on the severity and progress of the infestation. Prevention is essential, and a strong control plan will help to remove botfly eggs from your horse’s coat and vastly reduce the chances of infection.
If your horse is already suffering from an infestation, you must use a purpose-made de-worming medication containing active ingredients like ivermectin or moxidectin to treat it before it causes serious health concerns. Speak to your trusted equine vet about the best botfly deworming solutions for your horse’s needs.
At Ayr Equestrian, we recommend using a combination of preventive practices and vet-approved treatments to keep horse botfly at bay and ensure your equine friends are healthy and pest-free.
