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Red Firebug — A New Idaho Invader?


The red firebug, Pyrrhocoris apterus (Heteroptera: Pyrrhocoridae), is an introduced and invasive true bug with a vividly colored red and black body. Red firebugs are about ¼” to ½” in length depending upon the life stage, with adult females being the largest. The native range of these insects extends from Europe, eastward through Mongolia, and into northwestern China. It was first discovered and identified in the United States in 2008 near Salt Lake City, Utah. Exactly how these insects entered the country is unknown. Since their introduction and establishment, this insect has expanded its known range in the United States to include southern Idaho, with numerous specimens and populations first found in 2021 near Twin Falls and Burley, ID.

Red firebug adult
Figure 1. Brachypterous red firebug adult. Photograph by Erik J. Wenninger, University of Idaho.

Red firebugs are strikingly colorful, with alternating black and red coloration (Figure 1). Adult females and males can be polymorphic with respect to their wing development. They may be apterous (wingless), brachypterous (short-winged), or macropterous (fully winged). Most populations have been reported to be 90% apterous, 5% brachypterous, and 5% macropterous. The antennae, head, and lower portions of legs of the red firebug are entirely black. The antennae are four-segmented and the two compound eyes are black and protrude from the side of the head. Another feature that may help identify red firebugs is their lack of simple eyes (ocelli), which—in many other species of bugs—appear as black dots directly on the top of the head. As seen from above (dorsal view), the pronotum, thorax, and abdomen are red along the margins; two prominent black spots and two smaller spots on the wings (hemelytra) characterize the coloring of adult red firebugs.

Red firebug nymph
Figure 2. Red firebug nymph, showing the developing external wing pads and three black dots on the abdomen. Photograph by Erik J. Wenninger, University of Idaho.

Life Cycle and Host Plants

Red firebugs go through “incomplete” (hemimetabolous) metamorphosis with three life stages (egg → nymph → adult) and have one generation per year in temperate regions. Eggs are very small, ~1⁄32” (1 mm), almost invisible to the naked eye and are white in color. Eggs hatch about two weeks after they are laid, turning a salmon color as they develop. Nymphs are bright red and, as with most true bugs, their wings develop externally as wing pads (Figure 2). Nymphs undergo a total of five nymphal instars, molting each time and developing into adults in about two weeks, depending upon ambient temperatures and adequate food supply. In Idaho, nymphs may resemble nymphs of native boxelder bugs (see UI Extension CIS 1155, Boxelder Bug: Nuisance Management for Homeowners), Boisea trivittata, but red firebugs appear overall redder with a red-margined pronotum and black dots on the dorsum of the abdomen.

After reaching adulthood, adults begin mating in the late summer or early fall. As temperatures and day length decrease, red firebugs search for protected overwintering sites (including homes/sheds/shops and the like). In the early spring, females begin laying eggs for the new generation; each female may lay hundreds of eggs, mainly upon the soil surface.

Red firebugs aggregating on a linden seed
Figure 3. Brachypterous red firebugs aggregating on a linden (Tilia spp.) seed. Photograph by Erik J. Wenninger, University of Idaho.

As with all true bugs, red firebugs have piercing-sucking mouthparts they insert into food sources to feed. They feed on seeds from a wide variety of plants but are most known for feeding on plants in the (mallow) plant family. Idaho has several dozen species of ornamental, rangeland, and weed plants that could potentially be acceptable host plants for red firebugs, including mallow, globe mallow, checker-mallow, hollyhock, hibiscus, and linden trees. Scientific reports about this insect note they aggregate on black locust (Robinia pseudoacacia), spruce trees (Picea spp.), and linden trees (Tilia spp.), all common ornamentals in Idaho and prominent host plants in the red firebug’s native range; the firebugs mostly feed on linden seeds that have dropped to the ground (Figure 3). Feeding on host plants found in Idaho is unlikely to cause damage that would warrant management actions. Red firebugs may eat other insects (dead or alive), including each other, especially if food sources are limited. This varied diet and feeding habit (polyphagy) has likely contributed to the red firebug’s expansion and invasiveness throughout the world.

Pest Status, Management, and Possible Expansion throughout Idaho

Although red firebugs are unlikely to damage host plants in Idaho, they may become a nuisance pest. Red firebugs form large aggregations near plants and during late fall they may enter homes or other structures when seeking overwintering sites. Moreover, if handled roughly or disturbed, they may release a foul odor from scent glands on the first thoracic segment of their body. They also can regurgitate unpleasant smelling fluids from their gut. This combination of gathering in buildings and releasing foul-smelling odors makes the red firebug a potential nuisance pest. Currently, there are no legal insecticides registered in Idaho for homeowner or commercial use to manage this insect.

If large populations exist near homes/buildings, we recommend implementing several management strategies (Integrated Pest Management) to help control red firebugs as nuisance pests. First and foremost, “bug proofing” your home/building by sealing entry points is a key strategy. Improving weather stripping on loose-fitting exterior doors, caulking around windows, and repairing screen doors should reduce the ability of the bugs to enter homes/buildings. Using a standard shop vacuum to physically remove the bugs from homes/buildings will prevent foul odors or regurgitates from permeating or staining carpets and furniture. Deploying sticky traps around windowsills or entry points will physically capture red firebug adults as they try to enter for overwintering purposes. Using diatomaceous earth as a barrier insecticide treatment around homes is a least-toxic alternative chemical approach. Lastly, several active ingredients are listed for use in Idaho as broad-acting nerve poisons or insect growth regulators for barrier insecticidal treatments. To be a lawful application, the label must specifically list the pest insect type and application location and must be labelled for home use. All pesticides, including least-toxic alternatives, have benefits and potential hazards. Please read and follow the pesticide label for specific directions, paying close attention to the directions for use and application rates. Inconsistent use of a product or disregarding the label is a violation of both state and federal laws.

Since their initial discovery in the United States near Salt Lake City, Utah, in 2008, this insect has spread throughout surrounding areas, including southern Idaho. As of 2021, sightings of red firebugs in Idaho had only been reported in and near Twin Falls and Burley. Given the current establishment of this insect, wide availability of host plants, cold tolerance (5°F [-15°C] for up to two weeks), as well as genetic and phenotypic plasticity, it could be hypothesized that this insect might continue its expansion throughout Idaho. Fully winged individuals are good flyers and the long photoperiods and high temperatures that are typical of southern Idaho summers are surely favorable to their spread throughout the state.

About the Authors

Bradley S. Stokes—University of Idaho (UI), UI Extension Elmore County, Mountain Home, ID

Erik J. Wenninger—UI Department of Entomology, Plant Pathology and Nematology, Kimberly Research and Extension Center, Kimberly, ID


ALWAYS read and follow the instructions printed on the pesticide label. The pesticide recommendations in this UI publication do not substitute for instructions on the label. Pesticide laws and labels change frequently and may have changed since this publication was written. Some pesticides may have been withdrawn or had certain uses prohibited. Use pesticides with care. Do not use a pesticide unless the specific plant, animal, or other application site is specifically listed on the label. Store pesticides in their original containers and keep them out of the reach of children, pets, and livestock.

Trade Names—To simplify information, trade names have been used. No endorsement of named products is intended nor is criticism implied of similar products not mentioned.

Groundwater—To protect groundwater, when there is a choice of pesticides, the applicator should use the product least likely to leach.

BUL 1019 | Published March 2022 | © 2022 by the University of Idaho

Issued in furtherance of cooperative extension work in agriculture and home economics, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Barbara Petty, Director of University of Idaho Extension, University of Idaho, Moscow, Idaho 83844. The University of Idaho has a policy of nondiscrimination on the basis of race, color, religion, national origin, sex, sexual orientation, gender identity/expression, age, disability or status as a Vietnam-era veteran.
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