Atrytone arogos iowa (Scudder, 1868)
Basis for Listing
There are two subspecies of the arogos skipper, Atrytone arogos iowa (Scudder, 1869) and A. a. arogos. The range of subspecies iowa is roughly coincident with the midcontinent grassland biome, from North Dakota and eastern Montana east to Illinois and south to Texas; subspecies arogos is limited to the coastal states from New Jersey to Louisiana (Opler et al. 2006). Although the range of iowa is extensive, it is patchily distributed and generally considered uncommon to rare (subspecies arogos is now considered critically imperiled) (NatureServe 2008).
The Iowa skipper is a medium- to small- sized skipper with a compact, tidy appearance. The forewing length in males is about 1.3 cm (0.5 in.); females are slightly larger, with a forewing length of about 1.5 cm (0.6 in.). Beneath, the sexes are similarly light yellow without markings except for faintly lighter scaling along the hind wing veins. Above, the wings are yellowish orange, with broad, grayish-brown borders. The dark shading is more extensive in the female, diffusing into the orange central area, whereas the 2 tones are neatly differentiated in the male. The male lacks a stigma or brand on the forewing, and there are no light or translucent spots on the forewing of the female. Except for the European skipper (Thymelicus lineola) and the Delaware skipper (Anatrytone logan), all skippers likely to be confused with the Iowa skipper have brands in males and pale spots in females. The European skipper is slightly smaller and more delicate than the Iowa skipper. The dark borders on the upper side are very narrow in both sexes of the European skipper, and dark scaling continues along the veins a short distance into the orange. The Delaware skipper is larger on average than the Iowa skipper. In Delaware skipper males, the dark border is narrower, and in females the boundary between the tones is sharp. The veins are dark, especially in the female. In the Delaware skipper, the dark tone is colder, more blackish, than in the Iowa skipper.
In Minnesota, the Iowa skipper is restricted to native prairie habitat, generally where conditions are mesic or dry-mesic. It has been reported only once from sand prairie. Grassland dominated by non-native grasses does not appear to be suitable for the Iowa skipper in Minnesota or elsewhere in the Midwest.
Biology / Life History
The Iowa skipper has a single annual generation in Minnesota. The adult flight can begin in late June and last until the end of July, but most records are from the first three weeks of July. The partly grown larva overwinters and completes development the following spring.
Conservation / Management
Small colony sizes and isolation due to past habitat loss are the primary threats facing the Iowa skipper in Minnesota. This is aggravated by continuing habitat destruction. All habitat that is not protected by permanent dedication for conservation is at risk of destruction for agricultural production, aggregate mining, or development. Small colonies are vulnerable to extirpation as a result of natural events (such as severe drought or hailstorms) or human caused ones (such as insecticide application), as well as from the vagaries of normal population processes (for example, by chance all adults in one generation are males). Dispersal capabilities and propensities have not been investigated, but low numbers typical of most Iowa skipper colonies and the isolation of colonies in a landscape of non-habitat suggest that immigration is unlikely to help sustain colonies or to reestablish them in suitable habitat after extirpation events. Loss of genetic diversity is thus another possible threat.
Conservation Efforts in Minnesota
Many colonies of the Iowa skipper occur in prairies partly or completely protected as preserves by The Nature Conservancy; as Scientific and Natural Areas, State Parks, or Wildlife Management Areas by the Minnesota DNR; or as Waterfowl Production Areas or National Wildlife Refuges by the U.S. Fish and Wildlife Service. Detailed information about known occurrences within these protected areas is available to land managers. Most managers are knowledgeable about the potential negative impacts of prescribed burning on the arthropod fauna of prairies and follow guidelines to ameliorate threats. There has been an effort to educate all land managers regarding this. The Minnesota DNR has sponsored or supported a number of survey efforts to locate new populations of Iowa skippers and update information for previously known populations. Information about known occurrences is taken into account as part of the state environmental review process to help avoid negative impacts.
References and Additional Information
NatureServe. 2008. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.0. NatureServe, Arlington, Virginia.
Opler, P. A., H. Pavulaan, R. E. Stanford, and M. Pogue, coordinators. 2006. Butterflies and moths of North America: Arogos Skipper (Atrytone arogos). Bozeman, Montana: NBII Mountain Prairie Information Node.
Swengel, A. B. 1998. Effects of management on butterfly abundance in tallgrass prairie and pine barrens. Biological Conservation 83(1):77-89.