Geographic Range
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
Habitat
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
Physical Description
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.
- Other Physical Features
- ectothermic
- heterothermic
- bilateral symmetry
- polymorphic
- Sexual Dimorphism
- female larger
Development
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
Reproduction
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
- oviparous
Once egg laying is complete there is no further parental involvement.
- Parental Investment
-
pre-fertilization
- provisioning
-
protecting
- female
Behavior
Gasterophilus intestinalis
larvae are obligate internal parasites. Adults are free-living and non-parasitic.
The preferred hosts of this species are horses, giving it the common name of "horse
bot fly".
Food Habits
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.
- Primary Diet
-
carnivore
- eats body fluids
- coprophage
- Animal Foods
- blood
- body fluids
- Other Foods
- dung
Predation
Many species of insectivorous birds feed on the adults of this species.
Ecosystem Roles
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
- Equines (horses, donkeys, and mules)
Economic Importance for Humans: Positive
There are no obvious economic benefits to humans from horse bot flies.
Economic Importance for Humans: Negative
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
Conservation Status
This species is in no danger of extinction.
Other Comments
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.
Additional Links
Contributors
Sara Diamond (editor), Animal Diversity Web.
Harlen Hays (author), University of Michigan-Ann Arbor, Barry OConnor (editor), University of Michigan-Ann Arbor.
- Nearctic
-
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
- Palearctic
-
living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.
- Australian
-
Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.
- temperate
-
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
- tropical
-
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
- terrestrial
-
Living on the ground.
- tundra
-
A terrestrial biome with low, shrubby or mat-like vegetation found at extremely high latitudes or elevations, near the limit of plant growth. Soils usually subject to permafrost. Plant diversity is typically low and the growing season is short.
- taiga
-
Coniferous or boreal forest, located in a band across northern North America, Europe, and Asia. This terrestrial biome also occurs at high elevations. Long, cold winters and short, wet summers. Few species of trees are present; these are primarily conifers that grow in dense stands with little undergrowth. Some deciduous trees also may be present.
- tropical savanna and grassland
-
A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.
- savanna
-
A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.
- temperate grassland
-
A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.
- forest
-
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
- rainforest
-
rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.
- scrub forest
-
scrub forests develop in areas that experience dry seasons.
- agricultural
-
living in landscapes dominated by human agriculture.
- ectothermic
-
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
- heterothermic
-
having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.
- bilateral symmetry
-
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
- polymorphic
-
"many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph.
- metamorphosis
-
A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.
- semelparous
-
offspring are all produced in a single group (litter, clutch, etc.), after which the parent usually dies. Semelparous organisms often only live through a single season/year (or other periodic change in conditions) but may live for many seasons. In both cases reproduction occurs as a single investment of energy in offspring, with no future chance for investment in reproduction.
- seasonal breeding
-
breeding is confined to a particular season
- sexual
-
reproduction that includes combining the genetic contribution of two individuals, a male and a female
- fertilization
-
union of egg and spermatozoan
- internal fertilization
-
fertilization takes place within the female's body
- oviparous
-
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
- diurnal
-
- active during the day, 2. lasting for one day.
- parasite
-
an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death
- motile
-
having the capacity to move from one place to another.
- parasite
-
an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death
- causes or carries domestic animal disease
-
either directly causes, or indirectly transmits, a disease to a domestic animal
- carnivore
-
an animal that mainly eats meat
- coprophage
-
an animal that mainly eats the dung of other animals
References
Agneessens, J., S. Engelen, P. Debever, J. Vercruysse. 1998. Gasterophilus intestinalis infections in horses in Belgium.. Veterinary Parasitology , 77: 199-204.
Cogley, T., M. Cogley. 2000. Field observations of the host-parasite relationship associated with the common horse bot fly, Gasterophilus intestinalis.. Veterinary Parasitology , 88: 93-105.
Cogley, T., M. Cogley. 1999. Inter-relationship between Gasterophilus larvae and the horse’s gastric and duodenal wall with special reference to penetration.. Veterinary Parasitology , 86: 127-142.
Lyons, E., T. Swerczek, S. Tolliver, H. Bair, J. Drudge. 2000. Prevalence of selected species of internal parasites in equids at necropsy in central Kentucky.. Veterinary Parasitology , 92: 51-62.
Reinemeyer, C., P. Scholl, F. Andrews, D. Rock. 2000. Efficiency of moxidectin equine oral gel against endoscopically-confirmed Gasterophilus nasalis and Gasterophilus intestinalis (Diptera: Oestridae) infections in horses.. Veterinary Parasitology , 88: 287-291.
Roberts, L., J. Janovy, Jr. 2000. Gerald D. Schmidt & Larry S. Roberts’ Foundations of Parasitology, Sixth Edition . Boston: McGraw-Hill Companies.