Polyrhachis proxima ( Roger, 1863 )

Pham, Duy Long, Bao, Hoang Quoc, Nguyen, Dai Dac, Trong, Ly Van, Tra, Tran Thi Le, Phuc, Kieu Thanh, Thu, Nguyen Thi Minh & Chi, Nguyen Minh, 2024, Edible ants in Vietnam: Identification and indigenous knowledge, Ecologica Montenegrina 73, pp. 208-220 : 213-220

Polyrhachis proxima ( Roger, 1863)

HL: 2.197 –2.263 mm; HDW: 1.552 –1.561 mm; FW: 0.297 –0.308 mm ; SCL: 2.627 –3.012 mm; EL: 0.477 –0.484 mm ; IPPL: 1.253 –1.284 mm ; PEL: 0.599–0.63 mm; PEH: 0.691 –0.737 mm ; PNW: 1.441 – 1.461 mm ; PEW: 1.06–1.184 mm (n = 10, Fig. 4 ).

The body is greyish, adorned with dense hairs that impart a golden sheen and a highly polished texture dorsally. Head in full-face view rectangular to subrectangular. Mandible finely subtriangular shape and black, with five teeth. Eye relatively large, truncate posteriorly. Antenna with 12 segments, filiform, dark brown; Face distinctly elongated, with the eyes set well back laterally. Clypeus in profile sinuate, slightly concave anteriorly, moderately convex posteriorly with weakly impressed basal margin. Anterior clypeal margin arcuate. Frontal carinae prominent with moderately raised lobes. The pronotum, clear and adorned with two long spines, exhibits a shallow transverse depression anteriorly and dentate humeri. Metanotal groove deeply impressed, extending each side distal to metathoracic spiracles. Petiole biconvex with spines strong, long and acute, directed backward and upward. Head, mesosoma and gaster covered with moderately long, golden adpressed pubescence; Lateral pronotal profile with curved rugae, mesonotum and propodeum weakly curved rugae. Legs dark brown ( Fig. 4 ).

Products processed from ants and ant eggs in Vietnam

Products derived from ants and ant eggs in Vietnam showcase a rich diversity, reflecting the unique experiences, customs, and cultural nuances of each community ( Fig. 5 ). In northern Vietnam, Crematogaster rogenhoferi eggs are widely used in specialty dishes, such as cake-wrapped in Ficus auriculata leaves ( Fig. 5b ), filled with ant eggs, and steamed to perfection. Equally popular are dishes like sticky rice blended with processed ant eggs ( Fig. 5d ), or rice porridge infused with ant eggs, alongside bamboo shoots encased with ant eggs and steamed. Beyond these, ant eggs feature in various other culinary creations such as incorporation into soups or combination with chicken eggs for frying. While Polyrhachis proxima eggs are utilized in a similar way to C. rogenhoferi eggs, they are comparatively less common in Vietnam, commanding prices ranging from 8 to 15 USD/kg ( Table 1).

In Nghe An province, Odontoponera denticulata takes center stage, as its eggs, larvae, pupae, and adults are employed to concoct a distinctive ant soup-best savored for its tantalizing sweet and sour notes, exclusive to the Thai community in the province's western region. Oecophylla smaragdina , predominantly as adults, finds utility in marinating livestock meat, such as buffalo, cow, or deer, or transformed into ant salt as a fitting accompaniment for an array of dried and grilled meats in the Central Highlands ( Fig. 5f ). These products from O. smaragdina have been commercialized, and available for purchase in supermarkets ( Fig. 5g ). Furthermore, various delectable dishes have been crafted from this ant species, including ant egg salad, ant eggs cooked with Aganonerion polymorphum leaves, and ant eggs paired with bamboo shoots. Ingredients sourced from O. smaragdina fetch prices ranging from 8 to 9 USD/kg ( Table 1).

Discussion

This study has identified four ant species commonly utilized as food by indigenous populations in the provinces of Lao Cai, Phu Tho, Bac Kan, Nghe An, and Dak Lak, Vietnam. These species include Crematogaster rogenhoferi , Oecophylla smaragdina , Odontoponera denticulata , and Polyrhachis proxima . In Lao Cai, Phu Tho, and Bac Kan provinces, C. rogenhoferi eggs were frequently incorporated into numerous specialty dishes. P. proxima eggs were also utilized, albeit to a lesser extent due to being less abundant in northern Vietnam. In Nghe An province, eggs, pupae, and adults of O. denticulata are served as household food items. Conversely, nearly all adults of O. smaragdina are utilized as a spice in Dak Lak province. Both C. rogenhoferi and O. smaragdina exhibited a wide distribution and high natural density, thereby constituting a rich source of material to fulfill local demand. Different host tree species were found to be favored by these ant species: C. rogenhoferi nests are commonly found on Melia azedarach ( Fig. 6a ), Dimocarpus longan ( Fig. 6b ), bamboo trees ( Fig. 6c ), and various fruit trees; O. smaragdina prefers Styrax tonkinensis ( Fig. 6d ), Eucalyptus and Acacia trees ( Fig. 6e, f ), along with multiple fruit and industrial tree species.

Various studies have shown that adult ants and their eggs are rich in nutrients that may support human health ( Shen et al. 2006; Yin et al. 2017). Nutritional ingredients in P. vicina ant adults and eggs include amino acids, minerals, superoxide dismutase, and vitamin E ( Oranut et al. 2010). Analytical results have shown that ant powder contains 1.6g / 100g total acid, 6.3g / 100g ash, 13.2g / 100g essential oil, 9.0g/ 100g fat, 77000 IU/ 100g SOD, and 56.6g / 100g protein. There are 18 amino acids, in which, aspartic acid, alanine, glutamic acid, glycine, leucin, proline and tyrosine are the primary components. Among the 16 minerals, Ca, Fe, K, Mg, Mn, P, and Zn dominate. More than 20 organic components have been identified, the especially 9-octadecenoic acid, ethyl oleate, cholesterol and n-hexadecanoic acid ( Shen et al. 2006). Therefore, P. vicina is preferred for pharmaceutical products that are increasing in value and demand in China ( Zimian et al. 1997). Moreover, it is also used as a daily food source with consumers ( Yin et al. 2017). Further studies are needed to clarify nutriental profiles of the four edible ant species in this study.

This study has documented the widespread utilization of C. rogenhoferi and O. smaragdina as food by indigenous communities in Vietnam. These ants not only feature prominently in numerous specialty dishes but also serve as the basis for commercialized products. In addition to Vietnam, eggs of Crematogaster spp. are commonly consumed in Laos, Myanmar, and Thailand ( Yhoung-Aree and Viwatpanich 2005). Notably, O. smaragdina ant eggs are esteemed for their high nutritional value in Thailand, where they are recognized as a valuable source of additional nutrition ( Chansakulporn and Charoenying 2012), particularly for young children (Lao-araya and Trakultivakorn 2012).

Local people in Nghe An province favor inclusion of O. denticulata for some beloved dishes, while P. proxima eggs are utilized in a similar way to C. rogenhoferi eggs in the northern provinces of Vietnam. The eggs of some Polyrhachis species are noted for their exceptionally high nutritional and economic value ( Xiang et al. 2014; Wong and Guenard 2020; Zhang et al. 2022). However, there has been no record of O. denticulata and P. proxima being utilized as a food source outside of Vietnam.

Local communities residing near forests in Vietnam recognize the potential for harvesting and utilizing ants and their eggs, and they are committed to protecting and sustainably harvesting these edible ants. In addition to their culinary uses, many edible ant species are also valued as natural enemies ( Ray and Chatterjee 1989; Chansakulporn and Charoenying 2012; Kamiyama et al. 2021; Bolton 2024). They can play an important role in integrated pest management, similar to what entomopathogenic bacteria and fungi have been applied in agriculture and forestry (Chi et al. 2022; Chi et al. 2023; Chi et al. 2024). This study also documented several ant farming initiatives in Vietnam, with promising initial results. By cultivating edible ants, communities can contribute to sustainable development, meeting human demand while simultaneously maintaining ecological balance.

Conclusion

This study sheds light on the culinary practices surrounding the consumption of ants and their eggs among indigenous populations in Vietnam. Four ant species Crematogaster rogenhoferi , Oecophylla smaragdina , Odontoponera denticulata , and Polyrhachis proxima are most commonly utilized as food. These ants not only serve as nutritional supplements but also hold economic significance for commercialization efforts in some regions. Furthermore, the study highlights the nutritional value of ant-derived products, emphasizing their potential in both culinary and pharmaceutical industries. The involvement of local communities in sustainable harvesting and farming initiatives underscores the importance of balancing human consumption with ecological conservation.

Acknowledgments

This work was supported by the Lao Cai government under decree number 2500/QD-UBND dated 16/10/2023. The authors express their gratitude to thank Dr. Katsuyuki Eguchi for his valuable assistance in identifying the ant species, and Dr. John Grehan for English language editing.

Conflict of interest

On behalf of the authors, there are no conflicts of interest.

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Figures

Figure 4. Polyrhachis proxima (Roger, 1863) in Lao Cai province, Vietnam.

Figure 5. Products from edible ants: a. Pre-processing and processing of ant eggs; b. Cakes filled with ant eggs and wrapped with young leaves of Ficus auriculata tree; c. An ant egg processing competition held in Bac Kan province; d. Cakes made from ant eggs and processed into a dishes, along with colorful rice, are elegantly arranged on a large plate featuring a map of Vietnam; e. Dishes made from ant eggs served in restaurants; f, g. Products from Oecophylla smaragdina being sold in supermarkets.

Figure 6. Ant nests and host plants: a, b, c. Crematogaster rogenhoferi; d, e, f. Oecophylla smaragdina. a. Melia azedarach tree; b. Dimocarpus longan tree; c. Bambusa bambos trees; d. Styrax tonkinensis tree; e. Eucalyptus hybrid tree; f. Acacia mangium tree.