Listed as Vulnerable because the population size is estimated to number fewer than 10,000 mature individuals, there is a continuing decline of mature individuals estimated at >10% over the last three generations (15 to 30 years), and no subpopulation is estimated to contain more than 1,000 mature individuals.

This snake is endemic to the southeast of the United States. It occurs on the Coastal Plain from eastern North Carolina to southern Florida (Lake Okeechobee), west to southeastern Mississippi (Conant and Collins 1991, Palmer and Braswell 1995, Tennant 1997, Ernst and Ernst 2003). It is now very rare (or possibly extirpated) in the western part of the range in Mississippi and Alabama.

This species is represented by a large number of collection sites, but the species appears to be no longer extant at many of these (Tuberville et al. 2000). Palmer and Braswell (1995) mapped several dozen collection sites in North Carolina. Adult population size is unknown but presumably is at least several thousand. This is a secretive, fossorial snake that is difficult to detect, so it may be more numerous than available observations indicate. Nevertheless, it appears to be uncommon to rare throughout much of the historical range. In Florida, Tennant (1997) rated it as uncommon to rare but occasionally locally common. Different survey methods may yield different impressions of abundance. For example, in west-central Florida, H. simus was locally common and one of the most frequently observed snake species during pedestrian surveys on roads, but it was seldom trapped by drift fences (Enge and Wood 2002, 2003). Population trend cannot be quantified with any confidence, but clearly there has been a substantial decline (Tuberville et al. 2000). Most records are based on specimens that were collected/observed a long time ago and probably reflect only historical presence, as recent records for many of these sites are lacking (Tuberville et al. 2000). No recent (1983-1998) records are available for Mississippi, Alabama, and much of the historical range within Georgia. The species was considered quite common in southwestern Georgia in the 1940s and 1950s, but only a few occurrences have been noted in this area since 1970 (Tuberville et al. 2000). In South Carolina, the species has been seen recently (since 1980) in only 10 of the 20 counties from which it was once known. The population is apparently stable at the Savannah River Plant site in South Carolina. This snake apparently has declined in abundance throughout the range. Current trend data are unavailable, but this snake appears to be declining in area of occupancy, number of subpopulations, and abundance (Tuberville et al. 2000). However, data on commercial collection for the pet trade indicate that this snake is still locally common in at least three areas of Florida (Enge and Wood 2003). Assuming a generation time of around 5 years, the rate of decline over the past three generations (15 years) is unknown but may exceed 10%.

This snake inhabits open, xeric habitats with well-drained, sandy or sandy-loam soils such as sand ridges, stabilized coastal sand dunes, pine flatwoods, mixed oak-pine woodlands and forests, scrub oak woods, and oak hammocks; also old fields and river floodplains (Ashton and Ashton 1981, Palmer and Braswell 1995, Tennant 1997, Ernst and Ernst 2003). This snake spends considerable time burrowed in the soil.

Based on Heterodon nasicus, females probably mature at two to three years, and some individuals likely live well into their second decade. Hence generation length may be five to ten years.

Significant threats remain poorly understood. Predation of eggs and hatchlings by red imported fire ants (IFA) may be a factor in the decline (Tuberville et al. 2000). The snake's disappearance from certain areas is associated with heavy red IFA infestations. Other factors suggested to be of potential importance include loss of habitat to intensive agricultural/silvicultural activities, widespread pesticide application, road mortality, and the general persecution of snakes by humans. This species apparently can persist in areas of fragmented and altered upland habitats, although cumulative road mortality may be a significant factor, especially for hatchlings (Enge and Wood 2003).

Probably some occurrences are in protected areas. However, this snake appears to have disappeared in some large protected areas with relatively pristine habitats (Gibbons et al. 2000). Conservation needs include the following: 1) protecting large tracts of suitable habitat; 2) limiting pesticide use in preferred habitat types; 3) educating the public regarding snake's harmlessness; and 4) controlling fire ants on certain parcels of important habitat. Research is urgently needed to determine the factor or combination of factors responsible for the precipitous decline. Once the cause(s) is known, appropriate pro-active management measures may be implemented, and activities shown to be deleterious may be avoided. Specific research on the relationship, if any, between the disappearance of this species and the appearance of imported fire ants is needed.