Solenopsis tonsa

Solenopsis tonsa

Solenopsis tonsa is a tiny thief ant species belonging to the Solenopsis pygmaea species complex. Workers measure just 1.38-1.74mm and are pale yellow with a distinctive dense covering of short hairs that gives them a golden-haired pincushion appearance under magnification ^[1]. The most recognizable feature is the median hair-free strip running down the center of the head. This species is one of the few truly subterranean Solenopsis, spending most of its life underground in sandy soils ^[2]. Queens are larger and dark reddish-brown with hyaline wings, while males are dark reddish-brown with cream-colored legs and antennae ^[1].

What makes S. tonsa particularly interesting is how its discovery came about, researchers noticed workers in certain vials had many more dirt granules trapped in their unusually dense hairs, prompting a closer look that revealed this previously unrecognized species ^[1]. This is a cryptic, rarely collected species that appears to be restricted to sandhill habitats in the southeastern United States.

Quick Summary

• Difficulty: Expert
• Origin & Habitat: Native to the southeastern United States (Florida, Alabama, Texas). Found in sandhill habitats with light brown moist sandy soils at elevations around 1500 feet. One of the few truly subterranean Solenopsis species, occurring more frequently at 20cm soil depth than 10cm ^[2][3].
• Colony Type: Colony structure is unconfirmed. As a member of the Solenopsis pygmaea complex, likely single-queen (monogyne) like other thief ants, but this has not been documented.
• Size & Growth:
  • Queen: Queens are large relative to workers, head length 0.72mm, mesosoma length 1.44-1.46mm ^[1]. Estimated based on limited specimens.
  • Worker: 1.38-1.74mm total length ^[1]. Among the smallest ants in North America.
  • Colony: Unknown. Based on related Solenopsis species and its subterranean lifestyle, colonies are likely small, probably under 100 workers.
  • Growth: Unknown. Inferred from related species as slow to moderate.
  • Development: Estimated 6-10 weeks at optimal temperature based on genus-level patterns for small Solenopsis species. (Direct development data does not exist for this species. Temperature-dependent inference from related species suggests moderate development time.)
• Antkeeping:
  • Temperature: This is a cool-adapted subterranean species. Research shows occurrence decreases as soil temperature increases ^[2]. Keep nest around 18-22°C, avoiding warmer conditions. A gradient allowing cooler areas is beneficial.
  • Humidity: Requires moderate to high substrate moisture. Found in moist sandy soils in nature. Keep the nest substrate consistently damp but not waterlogged. Provide some drier areas for the ants to self-regulate.
  • Diapause: Unknown. Based on its southern distribution and subterranean lifestyle, likely minimal or no diapause. However, overwintering at cool temperatures (10-15°C) may be beneficial.
  • Nesting: Naturally nests underground in sandy soils. In captivity, provide a naturalistic setup with deep sandy substrate or a plaster/acrylic nest with moisture retention. Avoid dry, warm conditions. They are truly subterranean, they rarely come to the surface.
• Behavior: This is an extremely cryptic, subterranean species. Workers are rarely seen on the surface. They likely nest in small chambers underground and forage below the soil surface. As a thief ant, they probably steal food from other ant colonies' brood or caches. Escape risk is low due to their tiny size and subterranean habits, but they may squeeze through standard barrier setups, use fine mesh if housing in open setups.
• Common Issues: extreme difficulty in locating and collecting this species in the wild, lack of documented captive breeding success, virtually unknown in the hobby, sensitivity to warm and dry conditions, easily stressed by standard antkeeping temperatures, subterranean lifestyle makes observation and feeding challenging, very small size means escape prevention is still necessary despite limited surface activity

Discovery and Identification

Solenopsis tonsa was only formally described in 1989 by C.R. Thompson, who noted that this species may not be rare but merely previously unrecognized ^[1]. The discovery came about almost by accident, researchers noticed that workers in certain vials had many more dirt granules trapped in their unusually dense hairs, which prompted a closer examination that revealed this new species. Under magnification, workers look like a golden-haired pincushion due to their dense covering of short, erect hairs. The most distinctive feature is the median hair-free strip running down the center of the head, which is how the species got its name 'tonsa' (Latin for 'shaven') ^[1]. Workers are pale yellow to light yellowish brown and are among the smallest ants in North America at just 1.38-1.74mm.

Subterranean Lifestyle

This is one of the few truly subterranean Solenopsis species ^[2]. Research shows that occurrence increases by 145% from 10cm to 20cm soil depth, they go deeper as the soil surface warms ^[2]. They are most prevalent in sandhill habitats with light brown moist sandy soils ^[2][3]. This species is expected to occur strictly in sandhill environments ^[2]. The research also found significant negative effects on occurrence chances as soil temperature and moisture increased, meaning this species prefers cooler, moderately moist underground conditions rather than warm or waterlogged soils ^[2]. This makes it quite different from most ant species kept in captivity, which typically prefer warmer conditions.

Distribution and Range

Solenopsis tonsa is found across the southeastern United States. In Florida, it occurs from Leon County and Alachua County in the north south to Orange County ^[4]. In Alabama, it has been recorded in Baldwin and Mobile Counties in the southern part of the state ^[5]. Specimens have also been collected in Texas using subterranean baits at 1500 feet elevation in light brown moist sandy soils in forested areas ^[1]. The species appears to have a patchy distribution tied to specific sandhill habitats, which explains why it was only recently discovered and remains rarely collected.

Feeding and Diet

As a thief ant (Solenopsis genus), this species likely has an opportunistic diet similar to other Solenopsis, they probably consume small insects, honeydew, and may steal food from other ant colonies. Research shows that S. tonsa does not remove seeds, so they are not seed predators ^[1]. However, being truly subterranean, their diet likely consists of small soil arthropods, larvae, and possibly fungal growth. In captivity, offering small live prey like springtails or fruit fly larvae would be most appropriate. Given their tiny size, standard ant foods may be too large. Sugar sources might be accepted but this is unconfirmed. Feed small amounts of appropriate-sized protein and observe acceptance.

Reproduction and Nuptial Flights

Virtually nothing is known about the reproductive biology of S. tonsa. The original describer (Thompson,1989) never collected sexuals and suspects mating flights occur in late summer since the two females in his possession were fully sclerotized, had wings, and bore dates of August 15 (swept from a soybean field) and July 2 (from a nest collection) ^[1]. They are probably day flyers since they have never been taken in light traps. Queens are large and dark with hyaline (clear) wings. Males are dark reddish brown with hyaline wings and cream-colored legs and antennae ^[1]. The timing of nuptial flights remains unconfirmed.

Keeping This Species in Captivity

Keeping Solenopsis tonsa in captivity is extremely challenging and should be considered an expert-level undertaking. This species has virtually never been kept in captivity, there are no documented successful colonies in the antkeeping hobby. They require conditions that are opposite to most commonly kept ants: cool temperatures (18-22°C), consistent moisture in the substrate, and deep sandy soil to burrow into. They are truly subterranean and rarely come to the surface, making observation difficult. A naturalistic setup with deep sandy substrate would be most appropriate. Standard test tube setups may not provide adequate depth or the right moisture conditions. If you are able to locate a colony, be prepared for a completely experimental approach to husbandry. This species is best left to researchers and highly experienced antkeepers willing to document new observations. ^[1][2]

Frequently Asked Questions

References