Dermatobia hominis

Last updated:

Geographic Range

Dermatobia hominis are endemic to the highlands of Central and South America. Their range extends from southern Mexico to northern Argentina. (Bangsgaard, et al., 2000; Murdoch, et al., 1996)

Habitat

Dermatobia hominis, also known as the tropical warble fly or human bot fly, are found in tropical and semi-tropical areas of the New World. These places are typically coffee-growing highlands, as D. hominis prefer hilly, moist, and cool secondary-forests. (Catts, 1982; Dunn, 1934; Roberts and Janovy, Jr., 2000)

Physical Description

Adult D. hominis are 12-18 mm in length, are bluish in color, and resemble bumble-bees. They have three ocelli and a pair of large compound eyes, which are sexually dimorphic in that eyes are situated closer together in males than in females. Also, females are normally larger in size than males and bear a pseudovipositor at their posterior. As in other muscomorphans, the antennae of adult D. hominis each bear an arista -a tenuous, plumose projection- on the second of its three segments. The knob-like halteres, or functionally reduced hind-wings that are characteristic of dipterans, are also present. Peculiarly, the ancestral mouthparts have been lost in adult D. hominis, as well as in other cuterebrines.

Dermatobia hominis larvae, or maggots, are identified by the pyriform shape, the transverse rows of spines on their tegument, sclerotized mouthparts, and the pair of projecting spiracles at the posterior end. They may reach 25 mm in length and 7 mm in diameter. (Bangsgaard, et al., 2000; Catts, 1982; Murdoch, et al., 1996; Platt and Schmidhauser, 1997; Roberts and Janovy, Jr., 2000)

  • Sexual Dimorphism
  • female larger
  • sexes shaped differently
  • Range length
    12 to 18 mm
    0.47 to 0.71 in

Development

Dermatobia hominis reach sexual maturity soon after emergence from the puparium, and viable eggs may be laid as of the second day of adulthood. An egg, after being glued onto a paratenic host for transport to the vertebrate host requires 5-9 days to develop, after which it requires an additional 27-128 days to pass through the three larval stages inside the definitive host. Normally, about 12, 18, and 12 days are required for a larva to pass through the first, second, and third instars respectively. At the end of the larval period, the third larval instar exits the definitive host's body and drops onto the soil, after which it burrows deeply into the soil or other available debris and pupates within a period of 2-3 days. At the end of the pupation period, which takes somewhere between 27-78 days depending on seasonal variation in soil temperature, the adult emerges and becomes sexually active within two hours. (Catts, 1982)

Reproduction

Mating in D. hominis begins with "pouncing" displays performed by a male in response to sexual readiness in a female, which is indicated by the protraction of the latter's abdomen or pseudovipositor. Copulation is normally contingent upon female receptiveness; in other words, females seem to exhibit behavior suggestive of mate choice. Laboratory experimentation has revealed that males can pair with multiple mates in the average ratio of 1 male to 2.8 females. Perhaps due to the polygynous mating system, competition among males has been observed in the form of "pouncing" disturbances directed at copulating pairs. Copulation terminates after about 9 minutes. (Bangsgaard, et al., 2000; Catts, 1982; Curran, 1939; Roberts and Janovy, Jr., 2000)

Dermatobia hominis exhibit a homometabolous life-cycle. Being non-feeding and having a short adult life span (3-4 days in the laboratory), this stage in the life-cycle of D. hominis is allocated primarily towards reproductive efforts. Females lay 800 to 1,000 eggs.

Unique from other bot-fly species, which lay their eggs directly on the host or in the host's environment, is the peculiar egg dispersal strategy exhibited by females of the human bot fly; this process involves the use of porters (i.e., paratenic hosts) as vectors for transporting eggs onto the bodies of the vertebrate hosts. Under this strategy, a female captures a porter and glues her eggs onto one side of its abdomen using a water-insoluble glue, after which the porter is released without being harmed. Being sensitive to a sudden rise in temperature, the eggs instantly hatch upon contact with the warm-blooded body of a definitive host as the porter lands onto it, usually to feed on blood. Within 5-10 minutes, the larvae bore their way into the definitive host's body, often via the wounds inflicted by the porter's feeding, and establish themselves in the subcutaneous layer. Forty-eight species of flies--of which about half are mosquitoes--and a tick are reported to be involved in this paratenic relationship with female D. hominis. Porter species are often zoophilous, diurnal, moderate in size, and not too active. Potential advantages of this egg dispersal strategy include the protection of eggs from the elements and egg-parasitism, the prevention of egg loss from host grooming, and the adaptive allocation of energy in reproductive efforts. (Bangsgaard, et al., 2000; Catts, 1982; Curran, 1939; Roberts and Janovy, Jr., 2000)

  • Range eggs per season
    800 to 1000

Behavior

Food Habits

Like other species in the family Oestridae, adult D. hominis are non-feeding.

Larvae are endoparasites of birds and mammals. They bore into the skin of their hosts, either through pre-existing lesions in the skin or through active piercing, and become established in the subcutaneous layer. Breathing air through their posterior spiracles and employing body spines as anchors, D. hominis larvae use their sclerotized mouthparts to bore deeper into the host's body as they feed and grow on host tissue exudates. Feeding location on the host is not specific, as larvae have been found to establish at almost any exposed surface of the host's body, from the scrotum to the eye, although more frequently at more exposed regions of the body such as the leg and the back. (Bangsgaard, et al., 2000; Catts, 1982; Curran, 1939; Platt and Schmidhauser, 1997; Yildiz, et al., 1997)

  • Animal Foods
  • body fluids

Ecosystem Roles

Due to their unique egg dispersal strategy using mobile porters, D. hominis host range is more generalized than other bot-fly species. They have been found to parasitize many warm-blooded vertebrates and some birds (e.g., toucans and turkeys). And as suggested by the name, human bot fly, humans also frequently serve as hosts. (Bangsgaard, et al., 2000; Catts, 1982; Dunn, 1934; Roberts and Janovy, Jr., 2000)

Economic Importance for Humans: Negative

Infestation by D. hominis maggots, a form of myiasis, is a common condition in both humans and domesticated animals. It has been said that they surpass all other cuterebrines in terms of economic and public health importance. Dermatobia hominis larvae parasitize diverse regions on the human body, from the ankle to the brain of infants (through fontanelles, or gaps between incompletely formed bones of an infant's cranium) often causing tissue damage and bouts of severe pain from the boring activity of the larvae. In rare cases, fatalities have resulted, particularly from cerebral myiasis. Furthermore, lesions, or warbles, caused by the infestation may lead to secondary infections, which, if not treated with antibiotics, may result in fatality or other health complications. Treatment is by removal of larvae. Care must be excercised in doing so, since the larvae anchor themselves into the flesh using the spines on their tegument. Rupturing of larvae as the result of improper removal may lead to severe infection.

Although D. hominis infestation occurs among a broad range of domesticated animals, from dogs to sheep, their negative effects on the cattle industry is most severe in areas of the Neotropics. As a single animal may concurrently be infested by upwards of thousands of maggots, it is not suprising that losses have resulted from cattle mortality, from the rendering of the animal as unfit for slaughter, and from the destruction of the animal's hide. Negative impacts had been strong enough to cause a cessation in herding operations in Panama. (Bangsgaard, et al., 2000; Catts, 1982; Curran, 1939; Dunn, 1934; McMullin, et al., 1989; Murdoch, et al., 1996; Yildiz, et al., 1997)

Conservation Status

Contributors

Sara Diamond (editor), Animal Diversity Web.

Trong-Anh Mai (author), University of Michigan-Ann Arbor, Teresa Friedrich (editor), University of Michigan-Ann Arbor.

Glossary

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

agricultural

living in landscapes dominated by human agriculture.

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.

carnivore

an animal that mainly eats meat

causes disease in humans

an animal which directly causes disease in humans. For example, diseases caused by infection of filarial nematodes (elephantiasis and river blindness).

causes or carries domestic animal disease

either directly causes, or indirectly transmits, a disease to a domestic animal

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

fertilization

union of egg and spermatozoan

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.

internal fertilization

fertilization takes place within the female's body

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.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

parasite

an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death

polygynous

having more than one female as a mate at one time

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.

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.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

References

Bangsgaard, R., H. Bengt, E. Krogh, S. Heegaard. 2000. Palpebral myiasis in a Danish traveler caused by the human bot-fly (Dermatobia hominis). Acta Ophthalmologica Scandinavia, 78: 487-489.

Catts, E. 1982. Biology of the New World Bot Flies: Cuterebridae. Annual Review of Entomology, 27: 313-338.

Curran, C. 1939. The Human Bot Fly--How did this extraordinary insect develop the habit of forcing a mosquito to deposit its eggs for it?. Natural History, June: 45-48.

Dunn, L. 1934. Prevalence and importance of the tropical warble fly, Dermatobia hominis Linn., in Panama. Journal of Parasitology, 20: 219-226.

McMullin, P., L. Cramer, G. Benz, P. Jeromel, S. Gross. 1989. Control of Dermatobia hominis infestation in cattle using an ivermectin slow-release bolus. Veterinary Record, 124: 465.

Murdoch, D., R. Pilgrim, G. Paltridge. 1996. Cutaneous myiasis due to Dermatobia hominis: case report. New Zealand Medical Journal, 109: 465-466.

Platt, S., C. Schmidhauser. 1997. Local treatment of human botfly myiasis in Belize. Economic Botany, 51(1): 88-89.

Roberts, L., J. Janovy, Jr.. 2000. Gerald D. Schmidt & Larry S. Robert's Foundations of Parasitology, Sixth Edition. Boston: McGraw-Hill.

Yildiz, M., M. Basar, M. Hokelek, H. Basar, Z. Akalin. 1997. Scrotal myiasis. British Journal of Urology, 80: 493-494.