• Topics: Entomology and Nematology  | Biting and Stinging Pests  | Household Pests (IMG -- Vol. 1, Ch. II)  | Biting and Stinging Pests  | Pests of Humans and Domestic Animals (MG Entomology)  | Koehler, Philip G  | Oi, Faith 

Chiggers¹

Chiggers (Figure 1) or "red bugs" are the larvae of mites belonging to the family Trombiculidae. In humans, chiggers can cause intense itching and small reddish welts on the skin. In other parts of the world, chiggers transmit scrub typhus; however, in Florida they are not known to transmit disease. The intense irritation and subsequent scratching may result in secondary infection.

Figure 1. 

Chigger.

Biology

Adult chiggers usually overwinter in protected places and become active in the spring, although in Florida they may be active all year. The females lay eggs in a sheltered area. The eggs hatch into an ectoparasitic, six-legged larval form which is less than 1/50 inch long. The larva is the parasitic stage that feeds on humans and animals. The orange-yellow or light-red larval stage crawls on the soil surface until a suitable host is found. Suitable hosts range from small mammals to birds, reptiles, and amphibians. Humans are accidental hosts. Chiggers that attach to humans are usually dislodged or die within hours.

The larvae suck fluids from the skin of the host animal and do not burrow under the skin. Usually within three days the larva is engorged. The larva then drops from the host to the ground and transforms into the nymphal stage.

The nymph, like the adult mite, has eight legs. The bodies are usually hairy and about 1/20 inch long and bright red. The nymphs and adults feed on insect eggs, small insects, or other organisms.

The entire life cycle can require from two months to one year. As many as 1-5 generations may be produced per year depending on the temperature, moisture, and location.

Chigger Bites

Chiggers attach themselves to the skin, hair follicles or pores by inserting their piercing mouthparts. When chiggers attach to humans, they are not usually noticed for some time. During feeding, they inject a fluid into the skin which dissolves tissue. Chiggers feed by sucking up the liquified tissues. The human immune reaction to a bite prevents the chigger from obtaining adequate nourishment. They rarely survive long enough to complete a meal.

Itching from chigger bites is usually noticed 4-8 hours after chiggers have attached or have been accidentally removed. The fluid injection causes welts to appear which may last for two weeks (Figure 2). Some people exhibit an allergic reaction to the fluid which may result in severe swelling, itching, and fever. People mistakenly believe that chiggers embed themselves in the skin or that the welts contain chiggers. Often scratching at the welt results in secondary infection.

Figure 2. 

Chigger bites.

Chiggers prefer to attach on parts of the body where clothing fits tightly or where the flesh is thin, tender, or wrinkled. For this reason, chiggers locate in such areas as the ankles, waistline, knees, or armpits.

Preferred Habitat

Chiggers are most often found in low, damp areas where vegetation is heavy, although some species prefer dry areas. Chiggers seem to be most abundant in areas covered with shrubs and small trees where rodents are numerous. Chiggers occur in pockets or islands because a female will lay all her eggs in one spot; however, chiggers may persist in home lawns.

Control

Chiggers are easily removed from the skin by taking a hot bath or shower and lathering with soap several times. The bath will kill attached chiggers and others which are not attached. Since symptoms of contact may not appear for several hours, it is not always possible to completely prevent welts caused by chigger bites. Antiseptic should be applied to all welts which do appear. Temporary relief of itching may be achieved with nonprescription local anesthetics available at most drug stores. Studies have shown that meat tenderizer, rubbed into the welt, will alleviate itching.

If you are going into areas suspected of being infested with chiggers, wear protective clothing and use repellents (Table 1). Dusting sulfur is often used as a repellent. Repellents should be applied to legs, ankles, cuffs, waist, and sleeves by clothing application or directly to the body or clothing as directed by the label.

Chigger infestations may be eliminated by clearing brush from the area or closely mowing the area. Mowing removes the protective cover that chiggers need to survive. To locate infested areas, place a piece of black cardboard edgewise on the ground. If chiggers are present, they will climb to the top and congregate there. They will appear as tiny yellow or pink dots moving across cardboard. Before starting your survey for chiggers, use protective clothing and repellents.

Area control of chiggers is difficult to achieve, but insecticides approved for area control of chiggers are listed in Table 2. Apply these chemicals as directed on the label, and avoid getting insecticides into ponds and streams.

Also, attempt to exclude reptiles, amphibians, and small mammals that are preferred chigger hosts from the areas you will frequent. In some cases, fencing may be an option. Keep trash can lids secure to discourage unwanted wildlife from roaming your premises.

Chiggers sometimes invade structures. These infestations can be controlled with either surface or crack and crevice treatments of insecticides (Table 3) or space sprays (Table 4).

Tables

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.

U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Millie Ferrer, Interim Dean.

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