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Asteia Beata

Asteia beata are non-biting flies that are sometimes found indoors at windows during the winter. Little is known about this species but they are probably not pests beyond their presence.

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Updated:

August 14, 2024

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Figure 1. Adult Asteia beata. Photograph by Steve Scholnick via Flickr. Used with permission

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Classification

Common name: none

Scientific name: Asteia beata Aldrich, 1912

Order: Diptera (flies)

Family: Asteiidae (no common name)

Description

Asteia beata are small (2.4 mm), yellow and black flies (Figures 1, 2). They are smaller than other pest flies commonly found in homes and buildings, such as vinegar/fruit flies and scuttle flies (Figure 3). The eyes are green with two dark red stripes, although the colors may fade after death (Figure 4). The wing venation (which is difficult to see without magnification) is distinctive for the family Asteiidae (Figure 5).

closeup of an adult Asteia beata — Figure 2. Adult *Asteia beata*. Photograph by MJ Hatfield via Bugguide. Used under a CC BY-ND-NC 1.0 license.

Figure 3. Adult fly caught between a thumb and forefinger. Photograph by Michael Skvarla, Penn State University.

Head of an adult Asteia beata — Figure 4. Head of an adult *Asteia beata*. Note the green eyes with red stripes. Photograph by MJ Hatfield via Bugguide. Used under a CC BY-ND-NC 1.0 license.

Wing of Asteia beata — Figure 5. Wing of *Asteia beata*, with distinctive venation. Photograph by MJ Hatfield via Bugguide. Used under a CC BY-ND-NC 1.0 license.

Distribution

Specimens are uncommonly collected but have been found across much of northeastern and northwestern North America (Figure 6). A deep search of museum collections and additional collecting will likely expand the known range.

Range map of Asteia beata in the U.S. — Figure 6. Range of *Asteia beata.* Open circles represent state records without finer locality information. Records obtained from GBIF (2021) and Bugguide (2021).

Life history

Little is known about the natural history of Asteia beata. The larvae are undescribed and the larval food source is unknown. Adults of other asteiid species have been reared from fungi, the stems of cannabis (Cannabis sativa) and giant reed (Phragmites australis), buds of Gossypium infested with Anthonomus grandis, and fungi. It has been suggested that larval asteiids may be scavengers that feed on the frass (poop) of other insects.

Adult asteiids are found year-round during warm weather. They have been observed on flowers and tree sap flows, where they likely feed on nectar and sap (Figures 7, 8). Specimens are also collected at windows with enough frequency that the phenomenon has been noted in scientific literature.

Adult Asteia beata on a flower blossom — Figure 7. Adult *Asteia beata* on a flower. Photograph by Judy Gallagher via Flickr. Used under a CC BY 2.0 license.

Adult Asteia beata on a flower — Figure 8. Adult *Asteia beata* on a flower. Photograph by Stephen Luk via Bugguide, used with permission.

In addition to being found outdoors, adult Asteia beata are occasionally found indoors during cold weather, sometimes in large numbers. It is unknown how and why they occur indoors, but it has been speculated that their appearance may be tied to live Christmas trees. The discovery of the larvae and larval food source may shed light on this phenomenon.

Damage

Asteia beata adults do not cause damage and are only pests indoors because of their presence, if they are noticed at all.

Control

When found indoors, no control is necessary. As they lack necessary food resources such as live flowers, the adult flies will die out on their own without intervention.

References

Aldrich, J. M. 1914. New American species of Asteia and Sigalsoësa. Psyche, 22: 94–98.

Bugguide. 2021. Bugguide. Accessed 9 November 2021. For specific specimen records used, contact the author.

GBIF.org 2021. GBIF Occurrence Download. Accessed 10 November 2021.

Sabrosky, C. W. 1957. Synopsis of the New World species of the dipterous family Asteiidae. Annals of the Entomological Society of America, 50: 43–61.

Sabrosky, C. W. 1987. Asteiidae. In: J. F. McAlpine, B. V. Peterson, G. E. Shewell, H. J. Teskey, J. R. Vockeroth, and D. M. Wood. Manual of Nearctic Diptera, Volume 2. Research Branch Agriculture Canada, Canada Communication Group, Ottawa, Canada.

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