Eutrombicula splendens

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Geographic Range

Eutrombicula splendens is located in the Nearctic region including Canada and the United States. In the United States it occurs in the Great Lakes area, Mississippi river valley, plus many eastern and southern states. In Canada, E. splendens is mainly found in Ontario. (Jenkins, 1949)

Habitat

Typically associated with being near areas of permanent water and decaying wood and other forest debris (i.e. bogs, swamps), E. splendens requires a loose medium where this chigger can burrow. This type of habitat is characteristic of the soil of the region where it is found. Porous beds are an ideal location because it allows all instars to move freely. (Farrell and Wharton, 1949; Wrenn, 1974)

Before attaching to the host, the larval parasites prefer to find an area of very thin, wrinkled skin. Tightness of clothing is another factor affecting where this parasite feeds when humans are the host. (U.S. Public Health Service, 1940)

Physical Description

Larval Eutrombicula splendens appear light-orange to red and range from 150-600 μm (depending on level of engorgement). In some cases, the larvae are slightly pink or even white, a trait due to local genetic variation associated with an albino characteristic. The larval stage has three sets of legs, as opposed to the nymph and adult stages that follow the more ancestral arachnid forms of four pairs of legs (eight legs total). Dorsal-ventrally flattened, setae cover the legs and both dorsal (max of 26) and ventral (max of 16) sides. (Cunningham, et al., 2001; Jenkins, 1949)

Mites of the genus Eutrombicula are composed of the two ancestral segments: gnathosoma and idiosoma. The gnathosoma contains the mouthparts consisting of a pair of hooked mandibles and two palpi that have a pronged claw at the end. The idiosoma has all the legs attached to it throughout its life cycle as well as stigmata between the legs that serves as a tracheal system. Segmented legs are composed of coxa, trochanter, femur, genu, tibia, and tarsus. A dorsal sclerotized plate, the scutum, is the site for psuedostigmata and sensillary bases and the anal opening is further posterior. (Jenkins, 1949; U.S. Public Health Service, 1940; Wharton, et al., 1951)

  • Sexual Dimorphism
  • sexes alike

Development

Chiggers go through four developmental stages during their life cycle: egg, larva, nymph, and adult. The globular egg masses hatch in about a weeks time through an ecdysis and spitting of the shell in two. Emerging from the egg is the only parasitic stage of Eutrombicula splendens, the 6-legged larva. Only when the larval chiggers have fed can they molt and continue development. Upon engorgement the larval chiggers will drop from their vertebrate host and progress to the 8-legged nymph stage. From here on out the species is free-living, and nymphs molt into adults with the entire life cycle ranging from two months to one year depending on location. Warmer climates allow for a continuous cycle of development and reproduction, whereas E. splendens must overwinter in colder climates. In spring they may become active again. (Brennan and Reed, 1974; U.S. Public Health Service, 1940; Wharton, et al., 1951)

Reproduction

Throughout the genus Eutrombicula, reproduction takes place by way of spermatophore insemination. Adult males deposit the spermatophore sac, allowing a female to harvest and oviposit to complete fertilization. Mature males deposit spermatophores sequentially, with as many as 12 depositions in an hour, and intervals ranging from 2-3 minutes. On other occasions, males may go extended periods with out depositions.

During insemination, females approach and investigate the spermatophore. If adequate (seen by light tapping with the tarsi on the sac) the female will lower herself onto the sperm sac leading it into the genital opening with the genital plates spread apart (usually within a few seconds). (Lipovsky, et al., 1957)

Females lay fertilized eggs in the surrounding soil where they will eventually hatch. (Lipovsky, et al., 1957)

  • Breeding interval
    These chiggers are less active in colder regions and in the winter (0-3). Warmer conditions permit year-round activity (1-5).
  • Breeding season
    The breeding season is varies with the climate.
  • Range gestation period
    9 to 117 days

There is no parental involvement after the female lays eggs.

  • Parental Investment
  • pre-fertilization
    • protecting
      • female

Lifespan/Longevity

The lifespan for this species is unknown.

Behavior

Larval chiggers wait on top of the soil or vegetation in areas where vertebrate hosts are likely to pass in hopes of being able to secure a meal. Hosts are found by the presence of carbon dioxide. As a host passes, the larvae will shallowly bite at the surface skin for attachment where they will inject fluid into the wound using a stylostome to dissolve host tissues for consumption. After taking the meal (2-3 days) they drop off and progress with the next developmental stage. (Ewing, 1944)

Adults and nymphs in more northern climates will overwinter to spring. Species found further south will be active year round, with possibilities of many generations. Free living nymph and adult stages are not parasitic. (Ewing, 1944; Koehler, 1991; Sasa, 1961)

Communication and Perception

The eyes are indistinct with sensory functions carried out through sensillae. The eyes are attached to sensillary bases found in pits on the dorsally located scutum and function in tactile and chemo receptors. Setae covering the body may serve as tactile receptors also. (Jenkins, 1949; Wharton, et al., 1951)

Food Habits

Parasitic larvae usually prey on animal vertebrates with humans being accidental hosts. Some hosts include Didelphis virginiana (opossum), Scleroporus undulatus (eastern swift lizard), Terrepene carolina (box tortoise), among others. They engorge on a meal of tissue fluid from the chosen host via a stylostome, and complete feeding in 2-3 days. Stylostomes are a structure formed from host tissue, creating a straw-like feeding area in which a larva secretes a fluid to liquefy epidermal tissues. Arthropods are rarely ever the host in question. The other free-living nymph and adult stages are scavengers that feed on insect eggs, small insects, and also various plant material. (Durden and Wilson, 1990; Koehler, 1991; Rohani and Cromroy, 1979)

  • Animal Foods
  • eggs
  • body fluids
  • insects
  • terrestrial non-insect arthropods
  • Plant Foods
  • leaves
  • wood, bark, or stems

Predation

Predators of chiggers are those species that prey on mites, including salamanders, several species of beetles, spiders, and occasionally ants.

Ecosystem Roles

Eutrombicula splendens larvae are the most important cause of trombidiosis in the southeastern United States. They have been found on species of reptiles, birds, and mammals that are associated with decaying logs or similar habitat. Host specificity is relatively low with humans acting as accidental, but suitable hosts. (Koehler, 1991; Wrenn, 1974)

This species, as well as others within the genus, are not known to have any commensal or mutualistic habits with other individuals.

Species Used as Host
  • Vertebrates

Economic Importance for Humans: Positive

Humans do not benefit from this mite. (Ewing, 1944)

Economic Importance for Humans: Negative

In humans, Eutrombicula splendens causes trombidosis. Trombidiosis is characterized by an intense itching developing within the first 24 hours after larval feeding. It is the result of a liquefying agent secreted during the feeding processes. Inflammation follows shortly after as well as pinhead-sized papules and other small vesicles containing clear fluid. Fortunately this species does not transmit disease, thus only leaving a small irritation that peaks on the second or third day. (U.S. Public Health Service, 1940)

  • Negative Impacts
  • injures humans
    • bites or stings

Conservation Status

This species does not have any conservation status.

Contributors

Zack Durham (author), University of Michigan-Ann Arbor, Heidi Liere (editor), University of Michigan-Ann Arbor, John Marino (editor), University of Michigan-Ann Arbor, Barry OConnor (editor), University of Michigan-Ann Arbor, Renee Mulcrone (editor), Special Projects.

Glossary

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.

World Map

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.

bog

a wetland area rich in accumulated plant material and with acidic soils surrounding a body of open water. Bogs have a flora dominated by sedges, heaths, and sphagnum.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

detritus

particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).

diapause

a period of time when growth or development is suspended in insects and other invertebrates, it can usually only be ended the appropriate environmental stimulus.

diurnal
  1. active during the day, 2. lasting for one day.
ectothermic

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

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

herbivore

An animal that eats mainly plants or parts of plants.

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.

hibernation

the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.

indeterminate growth

Animals with indeterminate growth continue to grow throughout their lives.

internal fertilization

fertilization takes place within the female's body

marsh

marshes are wetland areas often dominated by grasses and reeds.

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.

molluscivore

eats mollusks, members of Phylum Mollusca

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

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

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

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

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).

terrestrial

Living on the ground.

year-round breeding

breeding takes place throughout the year

References

Brennan, J., J. Reed. 1974. The genus Eutrombicula in Venezuela (Acarina: Trombiculidae). The Journal of Parasitology, 60 (4): 699-711.

Cunningham, M., L. Phillips, C. Wellbourn. 2001. Trombiculiasis in the Florida black bear. Journal of Wildlife Diseases, 37 (3): 634-639.

Curtis, J., T. Baird. 2008. Within-population variation in free-living adult and ectoparasitic larval trombiculid mites on collared lizards. Herpetologica, 64 (2): 189-199.

Dohany, A., H. Cromroy. 1976. New records of chiggers (Acarina: Trombiculidae) from Florida. The Florida Entomologist, 59 (2): 183-190.

Durden, L., N. Wilson. 1990. Ectoparasitic and phoretic arthropods of Virginia opossums (Didelphis virginiana) in central Tennessee. The Journal of Parasitology, 76 (4): 581-583. Accessed July 01, 2011 at http://www.jstor.org/stable/3282847.

Ewing, H. 1944. The trombiculid mites (chigger mites) and their relation to disease. The Journal of Parasitology, 30 (6): 339-365. Accessed July 01, 2011 at http://www.jstor.org/stable/3272686.

Ewing, H. 1942. Remarks on the taxonomy of some American chiggers (Trombiculinae), including the descriptions of new genera and species. The Journal of Parasitology, 28 (6): 485-493. Accessed July 01, 2011 at http://www.jstor.org/stable/3272909.

Farrell, C., G. Wharton. 1949. A culture medium for chiggers (Trombiculidae). The Journal of Parasitology, 35 (4): 435.

Jenkins, D. 1949. Trombiculid mites affecting man. III. Trombicula (Eutrombicula) splendens Ewing in North America. The Journal of Parasitology, 35 (2): 201-204.

Koehler, P. 1991. Chiggers. University of Florida Extension, 2: 1-3.

Lipovsky, L., G. Byers, E. Kardos. 1957. Spermatophores: The mode of insemination of chiggers (Acarina: Trombiculidae). The Journal of Parasitology, 43 (3): 256-262.

Mallow, D., D. Ludwig, M. Hayes, D. Crossley. 1984. Habitat selection of postlarval Eutrombicula alfreddugesi and Eutrombicula splendens from eight microhabitats in Georgia, USA (Trombiculidae, Acarina). Journal of the Georgia Entomological Society, 19 (4): 543-548.

Rohani, I., H. Cromroy. 1979. Taxonomy and distribution of chiggers (Acarina: Trombiculidae) in north central Florida. The Florida Entomologist, 62 (4): 363-376.

Sasa, M. 1961. Biology of chiggers. Annual Review of Entomology, 6: 221-244.

U.S. Public Health Service, 1940. Chigger Mites. Public Health Reports (1896-1970), 55 (29): 1312-1314. Accessed July 01, 2011 at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1996020/pdf/pubhealthreporig02782-0004.pdf.

Wharton, G., D. Jenkins, J. Brennan, H. Fuller, G. Kohls, C. Phillip. 1951. The terminology and classification of trombiculid mites (Acarina: Trombiculidae). The Journal of Parasitology, 37 (1): 13-31.

Wrenn, W. 1974. Notes on the ecology of chiggers (Acarina: Trombiculidae) from northern Michigan and the description of a new species of Euschoengastia. Journal of the Kansas Entomological Society, 47 (2): 227-238. Accessed July 01, 2011 at http://www.jstor.org/stable/25082641.