This has been an interesting
fall to say the least. With a very
active hurricane season, horse flies hanging around longer than usual, and bot
flies coming out later than usual! Most
of what I have seen started earlier this month.
But, if you haven’t seen the bot fly buzzing around and hovering over
your horse, you might have seen the yellow eggs they left on your horse. The bot fly, which resembles a honey bee, has
non-functional mouthparts and does not bite the horse, but can cause
significant internal damage to the digestive system. The eggs of the bot fly
are what we are more concerned with, since they contain the bot larvae that can
be dangerous to your horse’s digestive tract.
Bot flies usually lay eggs on the horse’s legs, flank and belly area,
but sometimes even in the mane, neck, chest, throat and other areas. There actually are three types of bot flies:
the common horse bot fly (Gastrophilis intestinalis), the throat bot fly (G.
nasalis) and the nose horse bot fly (G. haemorrhoidalis). The common and throat bot flies are found
throughout the U.S., but the nose bot fly is more common in the northern and
Midwestern states. The female bot fly
can lay between 150-500 eggs in her 7-10 day life cycle. What’s most important is that the eggs are
removed promptly, before the horse licks them and the larvae are allowed to
enter the mouth and start causing problems.
Bot eggs require two things
to hatch: friction and moisture. The
horse provides both of these if they lick or scratch an area with their
mouth. The small bot larvae will attach
to the horse’s tongue, burrowing into the tissues of the mouth. Some of the bot larvae found closer to the
head will even emerge and migrate on their own without the horse’s help. It takes about one to five days for the egg to
incubate before hatching, so its best to remove the eggs as soon as you see new
ones on your horse. After about three
weeks, they will leave the mouth area and travel to the stomach and the upper
portion of the small intestine. The
cycle is complete when the fully grown larvae pass through the horse feces and
burrow in the soil to pupate, then emerge as flies after a couple months.
Damages caused by bot larvae
can be extensive. Horses may lose weight
due to the inability to graze because of the pain in their mouth from the
burrowing larvae in the tongue, gum, or lips. They may rub or bite at objects to relieve
pain from the burrowing and injure themselves.
In the stomach, the larvae can cause obstruction of the flow of food,
colic, or even perforations of the stomach or small intestine wall. Ulcers, peritonitis, esophageal paralysis,
and even rupture of the stomach can occur in very severe cases.
Controlling bots is not
hard, but routine inspection for eggs and frequent removal is required to
minimize their effects. Breaking the
life cycle is the key. Sponging affected
areas of the horse with warm water will cause the eggs to hatch, and including
an insecticide with the water will kill any eggs exposed once hatched. If you’d
rather not use them, a quick method of removal is to either use a bot knife or
clip the area. Oral treatment and in
most cases prevention of the horse from bot infestation is done through certain
deworming products. Dichlorvos,
ivermectin, trichlorfon, and moxidectin are all effective for bots. It is
recommended to deworm both in the late summer and immediately after a killing
frost for best results. After such an
abnormal fall, we will see when that frost comes! Best wishes for controlling those bots in the
meantime.
Eileen A. Coite
County Extension Director, Sampson County
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