More repulsive then wry neck or roundworm, bot fly larva, also known as a warble, is the most disturbing parasite I have encountered in rabbits. Boy flies are much larger than your typical house fly and will lay their eggs directly on the host (your rabbit). The larva then hatches from the egg and burrows under the skin where it feeds off the rabbit. Although they rarely cause the rabbits pain, warbles may cause extensive damage by irreparably injuring vital organs as they grow under the rabbits skin.
Unusual lumps or swelling that may show up anywhere on the rabbits body with a small breathing hole that usually excretes pus or a brown sludge with small amounts of blood–this is the waste from the larva. Typically, there is also hair loss around the lump and breathing hole and you may also notice the head of the larva poking slightly out to breathe. The lump will gradually increase in size as the larva continues to grow. Eventually, after anywhere from 3 weeks to a couple months the boy fly warble will emerge, leaving a gaping hole, usually filled with pus.
The eggs may have been directly laid on the rabbit or the rabbit pick them up from running around outside.
There are several courses you can take in treating warbles: pull the warble out, block the warble’s breathing hole causing the warble to climb out in order to breathe, or allow the warble infestation to run its course.
- First Method is to pull out the warble. In 9 out of 10 cases, this procedure should be done by veterinary professional as the warbles are extremely hard to remove. The warbles have tiny hairs all over their body that allow them to grip and stick in their burrow. Additionally, their head is MUCH smaller than the rest of their body making it hard to get the body through the breathing hole. To make this already hard situation almost impossible, if you squish the warble, it could kill the rabbit because its bodily fluids are poisonous if they get into the rabbits blood stream. However, there are a few cases when pulling out the warble may be the best option, but it would be best to consult a vet to determine.
- Second Method is to block the warble air hole. This makes the warble come out on its own accord when it needs air, without causing extensive damage. There are multiple ways to block the air hole, including packing salt into the hole, then adding a little bit of water. You can also smother the hole in Vaseline or petroleum jelly, just make sure the rabbit doesn’t lick it! If this method is the route you choose, make sure you have Q-tips, paper towels, warm salt water (to cleanse the hole), antibiotic ointment, and tweezers on hand.
- Third Method is to allow the larva to come out by itself. This is the best method if the larva does not seem to be bothering your rabbit or is not in a critical location (around the mouth, eyes, nose, or reproductive organs). This method requires daily checking and cleaning of the wound until the bot fly comes out. Not overly difficult, just requires diligence and a strong stomach.
After the warble has left by natural or not-so-natural causes, it is crucial that you clean out the gaping hole left over just as you would a deep cut. This ensures that other flies don’t lay their eggs in the wound and helps the wound heal faster. After the fly first leaves the rabbit, flush the wound out with salt water to remove any gunk or pus remaining, using a Q-tip to help ensure nothing is left. Then, squeeze some triple-antibiotic ointment (without pain-reliever included!!) into the wound to treat infection and speed the healing process. You will need to clean out the wound and apply the ointment daily and be vigilant to ensure that your bunny is healing properly and is not experiencing an infection.
If you want to try pulling the warble out, here is a good description of the process–this post also describes the suffocation method: https://rabbittalk.com/threads/botfly-cuterebra-warble-removal-and-wound-care.26210/
If you prefer to wait and allow the warble to come out by itself, here is an amazing step-by-step list of the journey. Also includes great pictures of what a bot fly infestation looks like: https://www.timbercreekfarmer.com/warbles-rabbits-caused-bot-fly/
A great discussion of treatment and removal of bot fly warbles: https://rabbittalk.com/threads/bot-fly-warble.24381/
Triple Antibiotic Ointment, without pain reliever: https://www.amazon.com/Antibiotic-Scratches-Abrasions-Preventative-Polymyxin