The agreeable tiger moth (Spilosoma congrua) is a medium-sized moth belonging to the family Erebidae, subfamily Arctiinae, commonly known as the tiger moths. It was first described by the British entomologist Francis Walker in 1855 and is one of the most common white tiger moths found in North America. The species is easily recognised by its bright white wings, pronounced black eyes, white abdomen with rows of black spots, and a distinctive orange or yellow "bib" on the thorax just behind the head. These features separate it from its close relatives, the Virginia tiger moth (Spilosoma virginica) and the dubious tiger moth (Spilosoma dubia).
The agreeable tiger moth ranges across most of the contiguous United States, southern Canada, and there is some evidence of disjunct populations in India. It inhabits open woodlands, meadows, fields, roadsides, and suburban gardens. The larvae are generalist feeders, consuming a wide variety of herbaceous plants, including many common weeds and garden vegetables, which sometimes brings the species into mild conflict with agriculture. Adults are nocturnal and are attracted to lights. The species has one to three generations per year depending on latitude and climate.
Taxonomy and nomenclature
Original description Francis Walker, a prolific but sometimes careless describer of insects, named Spilosoma congrua in the fifth volume of his "List of the Specimens of Lepidopterous Insects in the Collection of the British Museum", published in 1855. The holotype, a female specimen, was part of the extensive collections assembled by naturalists in the eastern United States and sent to London. Walker gave a brief Latin diagnosis, noting the white colour of the wings, the black spotting of the abdomen, and the ochreous tint of the head and front of the thorax. The precise type locality was not recorded, but the specimen almost certainly originated from the northeastern United States, probably New York or New Jersey.Walker, F. (1855). List of the Specimens of Lepidopterous Insects in the Collection of the British Museum, Part V, pp. 668–669. London.
Etymology The generic name Spilosoma is derived from the Greek words spilos (a spot, stain, or blemish) and soma (body), referring to the spotted abdomen characteristic of many members of the genus. The specific epithet congrua is Latin for "agreeable", "congruous", or "fitting". The precise reason for Walker's choice of this name is unknown. It may refer to the pleasing symmetry of the black spots on the white body, or it may simply have been an arbitrary choice from the vocabulary of descriptive Latin terms. The common name "agreeable tiger moth" directly translates the scientific name and was adopted by early 20th century American entomologists. The alternative name "New Hope tiger moth" derives from a later synonym, Spilosoma spesnova, where spes nova means "new hope" in Latin. This name was proposed by Smith in 1985 for what was thought to be a separate species, but was later synonymised.
Classification within the Arctiinae The tiger moths (Arctiinae) are a large and diverse subfamily of the Erebidae. Within the Arctiinae, Spilosoma congrua belongs to the tribe Arctiini and the subtribe Spilosomina, which includes many of the familiar white and spotted tiger moths. The genus Spilosoma contains approximately 200 species worldwide, with about 20 occurring in North America. Molecular phylogenetic studies have not fully resolved the relationships within the North American white tiger moths, but S. congrua is clearly distinct from its sympatric congeners based on both genetic and morphological evidence.Schmidt, B. C. (2007). "Systematics of the North American moths of the subfamily Arctiinae (Lepidoptera: Erebidae)". Unpublished Ph.D. thesis, University of Alberta.
Subspecies and variation Several varieties and aberrations have been named, but none are currently recognised as valid subspecies. These colour forms include: bimaculata Stretch, 1906 – with two black spots instead of one on each forewing. flavofrons Neumoegen & Dyar, 1893 – with a yellow frons (front of head) instead of white. maculifrons Stretch, 1906 – with a heavily spotted frons. nigrifrons Stretch, 1906 – with a black frons. rubrofrons Packard, 1864 – with a reddish frons. fuscipennis Strand, 1919 – with smoky brown wings. hyalinipennis Strand, 1919 – with translucent wings.
These names represent minor individual variations and are not considered to have taxonomic standing. The degree of spotting on the abdomen and the intensity of the orange bib also vary among individuals and populations.
Physical description
Adult The adult agreeable tiger moth is a medium-sized macrolepidopteran. The wingspan ranges from 28 to 42 millimetres, with females usually slightly larger than males. The forewings are pure white, occasionally with a faint cream or yellowish tint along the costa. A small black spot or dot is present on the disc of each forewing, although it is sometimes faint or absent. The hindwings are white and unmarked. The wing shape is typical of the genus: the forewings are elongate and somewhat triangular, the hindwings rounded.
The head is small, with large, compound black eyes that are a distinctive feature. The antennae are filiform (thread-like) in the female and bipectinate (comb-like on both sides) in the male, a sexually dimorphic character common in moths. The frons (front of the head) is usually white, but as noted above, may be yellow, red, or black in some individuals. The labial palps are short and porrect (projecting forward).
The thorax is white, with a prominent patch of orange, ochreous, or yellow setae (hair-like scales) on the anterior part, just behind the head. This orange "bib" is the most reliable field mark for separating the species from the Virginia tiger moth, which has a white thorax. The underside of the thorax is white. The legs are white with black bands on the femora and tibiae.
The abdomen is white, with a dorsal row of black spots, one on each segment. There are also lateral rows of black spots on the sides of the abdomen. The number and size of the spots are variable, and some individuals are more heavily spotted than others. The tip of the abdomen in the female bears a tuft of white setae used to cover the egg mass.
Egg The egg is spherical, about 0.6 mm in diameter, and pale yellow when first laid, darkening to grey before hatching. The surface is smooth and shiny under low magnification. Eggs are laid in clusters on the underside of host plant leaves, usually in batches of 20 to 100. A single female may lay several hundred eggs over her lifetime.
Larva The larva of the agreeable tiger moth is the well-known "woolly bear" type, covered in dense setae (bristles). The first instar larvae are small (about 2 mm) and pale yellow, with sparse, short setae. As they grow and moult through successive instars (usually five to seven), they become darker and more densely hairy.
The mature caterpillar is about 30 to 35 mm long. The body is dark brown to black, covered in tufts of stiff, dark brown or black setae. Among these dark setae are interspersed shorter, paler setae, giving the caterpillar a somewhat frosted appearance. The head is small, black, and shiny. The prolegs are well developed. When disturbed, the caterpillar curls into a tight ball, a defensive behaviour typical of many arctiine larvae.
The colour and density of the setae can vary somewhat depending on the host plant and environmental conditions. Caterpillars raised on a diet rich in certain plant compounds may have slightly different colouration, though detailed studies on this are lacking.
Pupa The pupa is about 15 mm long, dark brown to black, and smooth. It is enclosed in a loose cocoon of silk mixed with the caterpillar's own shed setae. The cocoon is usually constructed in leaf litter, under loose bark, or in a crevice. The pupal stage lasts 10 to 21 days in the summer generations. In the overwintering generation, the pupa enters diapause and may remain dormant for several months.
Distribution
North America The agreeable tiger moth is widely distributed across the United States and southern Canada. In the United States, it occurs from Maine south to Florida, and west to Texas, Oklahoma, Kansas, Nebraska, and the Dakotas. It is also recorded from Colorado, Wyoming, and Montana, though it is less common in the arid western states. It occurs throughout the Midwest and the Great Lakes region. In the Pacific Northwest, it is absent or very rare.
In Canada, the species is found in Ontario, Quebec, New Brunswick, Nova Scotia, and possibly Manitoba and Saskatchewan, though northern records are sparse. The northern limit of its range appears to be determined by climate, with the species absent from the boreal forest and tundra regions.
Possible occurrence in India There is a record of Spilosoma congrua from India in the Barcode of Life Data System (BOLD).Spilosoma congrua at BOLD. This record requires verification. It may represent a misidentification, a recent introduction, or a natural disjunct population. The genus Spilosoma is well represented in the Oriental region, and several Asian species closely resemble S. congrua in appearance. Careful morphological and molecular comparison is needed to determine whether the Indian records truly belong to this species or to a closely related Asian taxon. As of 2025, no published study has definitively resolved this question.
Habitat The agreeable tiger moth inhabits a wide range of open and semi-open habitats. It is most common in: Old fields and meadows Roadsides and railway verges Forest edges and clearings Suburban gardens and parks Abandoned agricultural land Wetlands and marshes edges
The species avoids dense, closed-canopy forest and extremely arid deserts, although it may occur in riparian corridors through otherwise unsuitable terrain. The key requirement for habitat suitability is the presence of herbaceous host plants for the larvae.
In urban and suburban areas, the agreeable tiger moth is often one of the more commonly observed white moths at porch lights. It tolerates moderate levels of habitat disturbance and may benefit from the proliferation of weedy host plants in human-modified environments.
Life cycle and development
Voltinism The number of generations per year (voltinism) varies with latitude and climate. In the northern parts of its range (Canada, northern New England, the Great Lakes), the species is univoltine, producing a single generation per year. In the mid-Atlantic and midwestern states, it is bivoltine, with two generations. In the deep South, from the Carolinas to Texas and Florida, it may be trivoltine, with three overlapping generations in a long growing season. In southern Florida and the Gulf Coast, adults may be found in nearly every month of the year.
Adult activity Adults are primarily nocturnal. They fly from dusk until the early hours of the morning, with peak activity between 10 PM and 2 AM. Males are strong fliers and may travel considerable distances in search of females. Females are heavier and less active, usually remaining close to the site of emergence until they have mated and laid most of their eggs.
Adults are attracted to artificial lights, a behaviour that makes them easy to observe at porch lights, street lamps, and moth sheets used by entomologists. They rest during the day on tree trunks, under leaves, or on walls, where their white colour provides excellent camouflage against light-coloured surfaces.
Mating