Moxidectin equine gel can be used to reduce and potentially eliminate G. intestinalis from a host. It has been shown to have 88-100% efficiency in eliminating third instar larvae from the host body.
This species is in no danger of extinction.
US Federal List: no special status
CITES: no special status
Females attach eggs to the hairs of horses, mainly on the knees and lower parts of the front legs. The horse cleans itself by licking these areas. Enzymes in the horse's saliva and heat from its tongue will cause the eggs to hatch and the first larval instar burrow into the tongue's surface. Larvae then burrow their way to the stomach of the horse. Using mouthhooks, the larvae feed from the blood of the horse. Both the second and third larval instars remain in the horse's stomach. In the Northern hemisphere, third instar larvae can be found year round while second instars are not present for the months of April-July. Come spring, the larvae will pass out with the feces of the horse and pupate in the manure or loose soil. Pupation takes between three and five weeks.
Development - Life Cycle: metamorphosis
Gasterophilus intestinalis is extremely common. The majority of the time, its presence is insignificant enough not to harm the host. However, when found in large number G. intestinalis can cause harm to the host and eventual death.
In extremely rare cases G. intestinalis attaches eggs to a different type of host, including humans. The effects of horse bot flies in humans have not been recorded.
Negative Impacts: causes or carries domestic animal disease
There are no obvious economic benefits to humans from horse bot flies.
Bot flies can cause damaging parasitic infestations. if populations become large enough in a single host, it can cause significant health problems and even death for the host animal.
Ecosystem Impact: parasite
Species Used as Host:
Larvae feed on the blood of their host. Using their mouth hooks and spines, larvae attach themselves to the gut wall of the host's stomach. Once attached, an ulcer forms around the larvae. Adult males are non-feeding while adult females have been observed feeding from waste material.
Animal Foods: blood; body fluids
Other Foods: dung
Primary Diet: carnivore (Eats body fluids); coprophage
Gasterophilus intestinalis ranges throughout the Old and New World, but is most common in Western Europe and in the Southern and South Western United States.
Biogeographic Regions: nearctic ; palearctic ; australian
Adult flies are found in open areas near equines. First larval instars are found in the tongue of the host. Second and third larval instars are found in the non-glandular region of the stomach.
Habitat Regions: temperate ; tropical ; terrestrial
Terrestrial Biomes: tundra ; taiga ; savanna or grassland ; forest ; rainforest ; scrub forest
Other Habitat Features: agricultural
Adults range in size from 8 mm to 18 mm. Females are larger than males, and have a long pseudoovipositor. Both males and females have a constriction between the 1st and 2nd segments of their abdomens, separating it into a propodeum and a gaster. This is commonly referred to a "wasp-waist".
Larval instars are pill shaped. The majority of larval body segments have rings of barbs pointed toward the posterior. The last few segments do not have these spines.
Range length: 8 to 18 mm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry ; polymorphic
Sexual Dimorphism: female larger
Many species of insectivorous birds feed on the adults of this species.
Mating occurs shortly after the female emerges from her pupa. Mating commonly occurs in the same region as pupation becuase of the high density of emerging adults in the same area. Once mating has occurred, females immediately seek out a suitable host.
After copulation, females seek out a suitable host for her eggs. Females hover near the horses front legs with their body curved forming a "C" shape. This places the ovipositor in a perfect position to attach eggs. Each female will lay eggs at multiple sites on multiple horses. This will increase the reproductive potential of the species.
Key Reproductive Features: semelparous ; seasonal breeding ; sexual ; fertilization (Internal ); oviparous
Once egg laying is complete there is no further parental involvement.
Parental Investment: pre-fertilization (Provisioning, Protecting: Female)
Gasterophilus intestinalis, also known as horse bot fly, is a species of insect of the family Oestridae,[2] and is found worldwide.[3] The adults, which have a bumblebee-like appearance, are prominently active in the summer.[4] G. intestinalis is primarily a parasite of horses, mules and donkeys.[5]
The eggs of G. intestinalis are pale yellow in color,[6] and 1–2 mm (0.039–0.079 in) long.[4] The larvae are yellow or tan.[3] Adults, which are 10–15 mm (0.39–0.59 in) long,[5] look superficially like hairy bumblebees, with a noticeable ovipositor at the end of the abdomen.[4]
The female fly cements individual eggs onto hairs of the forelimbs and shoulders of horses, mules and donkeys.[6][5] Each female lays up to 1000 eggs.[6] In order to hatch, the eggs must be licked by the host animal.[5] If taken into the host's mouth during grooming, the egg will hatch in the mouth.[5] If not, the first instar larva will migrate to the mouth.[5] The larvae develop in the tissue the tongue,[3] in tunnels within 1.5 mm (0.059 in) of the surface.[7] Second instar larvae are swallowed and pass into the host's stomach,[3] and attach to the non-glandular region of the stomach.[8] The larvae remain in the stomach for 8–10 months,[5] before maturing into third instar larvae.[3] In the spring, the third stage larvae pass out of the host in the feces.[3] Pupation takes place in the soil for a duration of 3–5 weeks, until the adults emerge.[5] Adults are active for only a few weeks in the summer,[4] and, lacking functional mouthparts, live only for a short time.[5]
Clinical signs are uncommon in host animals.[3] Large numbers of larvae in the stomach can cause pain in the stomach,[3] and, rarely, extremely large infestations may cause an obstruction at the outflow from the stomach to the duodenum.[7] The larvae are usually found incidentally when the host's stomach is examined by endoscope.[3] Often the only sign of infestation is the finding of larvae in the feces.[4] The main impact on the host is the nuisance of the adults as they repeatedly land on the legs when attempting to lay eggs.[4]
Parasiticides which are effective against the larvae include macrolytic lactones, such as ivermectin and moxidectin, and organophosphates, such as metrifonate (also known as trichlorphon) and dichlorvos.[6] The best time to deworm horses against Gasterophilus intestinalis is after the first hard frost. This hard frost will kill the females so no new eggs can be laid on the horse that can be ingested. Meaning that the dewormer is acting on the larva attached to the stomach and will also decrease the amount of larva shed in the feces in the spring.[9]
Although deworming is the best treatment and prevention of bot flies, horse owners can take other steps to prevent bot fly egg ingestion. This can be done by manually removing the eggs from the horse's leg using specialized tools, such as bot knives.[9] However, it is important to wash your hands after physically removing the eggs because there is a possibility of the larvae burrowing into the human skin.[10] In addition to removing the eggs manually, there are a few management changes that can be made to decrease the amount of bot flies. Since part of the life-cycle is spent developing in the manure, manure should be removed from horse's pens regularly and composted before place on pasture land. If possible, rotational grazing with different species is beneficial. Lastly, making sure feed and water are free from contamination with manure.[9]
Gasterophilus intestinalis, also known as horse bot fly, is a species of insect of the family Oestridae, and is found worldwide. The adults, which have a bumblebee-like appearance, are prominently active in the summer. G. intestinalis is primarily a parasite of horses, mules and donkeys.
