This is a nectarivorous cave roosting species that forms compact clusters forming large colonies consisting of hundreds to tens of thousands of individuals. It can also form small colonies or join colonies of different species (e.g., Rousettus amplexicaudatus). Its preferred shelter are caves in forested habitat, but can be found in a variety of habitats and have been observed utilizing man-made structures such as: mines (Mickleburgh et al. 1992, Furey et al. 2011), the attics of village huts (Tarapada Bhattacharyya pers. comm. June 2005, Khim Maung Swe pers. comm. January 2000), the basement of a high-rise building (Lim 2015), and beneath a high vehicular bridge. A study in Mindanao, Philippines observed use of caves located near water that have large openings and multiple entry points (Tanalgo and Tabora 2015). Within the cave, this species prefers to cling to walls in areas of partial illumination (Tanalgo and Tabora 2015). In addition, it is known to roost high in the ceilings of caves in Thailand (Acharya Pers. obs. 2019).

The species has high aspect ratio wings and high wing loading capacity, making it a strong flyer capable of long-distance flight (Chakravarty et al. 2018). Individuals fly many kilometers in search of food each night and the longest foraging distance is from Malaysia was inferred to be ca 38 km based on finding of mangrove pollen at a land locked roost site (Start and Marshall 1974). Since then, radio telemetry has provided more insight to nightly foraging distances. The longest observed distance from study out of southern Thailand was 17.9 km, only half of the historical estimate (Acharya et al. 2015a). Nightly foraging distance has been found to correlate with roost size, the larger the roost, the longer the foraging distance. A study conducted in southern Thailand exemplifies this as bats from the largest roost were recorded traveling farther than those in smaller roosts (Acharya et al. 2015a). Although day roosting in large colonies may be beneficial, these colonies create increased competition for resources, hence the need to forage farther from the roost site (Fleming 1982, Wilkinson 1992).

Eonycteris spelaea is known to forage in agricultural areas, primary forest, secondary forest, and coastal mangroves (Smith and Xie 2008, Thavry et al. 2017). It forages individually or in small groups by landing on a flower for 2-3 seconds at a time (Acharya et al. 2015b). It is a generalist, taking advantage of any available food sources (Stewart and Dudash 2018), and is the most common pollinator of many chiropterophilous plant species in Southeast Asia (Gould 1978; Bumrungsri et al. 2009; Sritongchuay et al. 2008; Stewart and Dudash 2016; Acharya 2015a,b). Its diet varies across its distribution: it has been found to feed on 55 plant species in Malaysia (Lim et al. 2018), 19 plant species in Thailand (Pakarnseree 1986), 13 plant species in Cambodia (Thavry et al. 2017), and 18 plant species in China (Yunnan Province and Jinjhong City, Yang et al. 2017). Across its range. E. spelaea provides significant ecological services as it pollinates coastal mangroves, primary forests, and many economically important crops including durian (Durio zibethinus), tree bean (Parkia timoriana) and petai (P. speciosa, Harbit et al. 2008, Sritongchuay et al 2008, Bumrungsri et al. 2009, Bumrungsri et al. 2013, Nor Zalipah et al. 2016, Stewart and Dudash 2016, Thavry et al. 2017).

Reproduction occurs year-round and is often observed correlating with blooms of certain food sources (Bumrungsri et al. 2013, Heideman and Utzurrum 2003). Females produce one offspring (with which they can fly) per year (Bates and Harrison 1997).

It is not known to migrate seasonally as it is a generalist and switches food sources throughout the year. However, this may vary with location as in Xishuangbanna, China, about 1,000 individuals were found roosting in a cave with about 600 Rousettus leschenaulti in the winter with both species vacating the cave during the reproductive period, which corresponded to when the cave was occupied by Chaerephon plicata (Zhang et al. 2010).

There is evidence of significant sexual dimorphism in this species with the males (55.0-82.0 g) being larger than females (35.0-78.0 g, Rahman and Chaudhury 2017). It exhibits physical adaptations for nectar feeding including a long muzzle and sharply pointed tongue, with well-developed filiform papillae at the tip (Bumrungsri et al 2013). Their ears are simple and they do not have a tragus. The dorsal pelage is brown and the ventral is pale in color, males have longer and darker fur around the neck than females (Rahman and Chaudhurry 2017). The species two distinguishing features including large, kidney shaped glands on either side of the anus (Nameer et al. 2016) and has no claw on its second digit (Atmoko and Nugroho 2013).

Eonycteris spelaea is widespread and found in many protected areas (e.g., Kalakkad-Mundunthurai Tiger Reserve in Tamil Nadu; Vanitharani et al. 2005). However, there are few records, if any, of significant colonies (>1,000 [Thavry et al. 2017]) of the species within protected areas. It is widely accepted that, if not as a whole, subpopulations of this species are threatened due to multiple anthropogenic pressures and as a principal bat pollinator in Old World tropics, its conservation should be prioritized (Acharya 2015). Its direct ecological role on plant pollination (Acharya 2015) and all related benefits (gene flow of plant species, maintenance of landscape, local economy, etc) make this species a priority.

Direct conservation measures across its area of occurrence are necessary to prevent suspected and projected population declines. Main conservation priorities include public education, protection of colonies and their required resources, and the establishment of sustainable harvesting practices. Sustained public education and increased awareness of the commercial and ecological importance of pollinators are imperative to the conservation and protection of this species on a local level (Maharadatunkamsi 2003, Harbit et al. 2008, Thavry et al. 2017). Law enforcement efforts as well as effective management and protection are needed to prevent unregulated human disturbances at cave sites (Bumrungsri et al. 2009,2013; Furey et al. 2011; Tanalgo and Tabora 2015; Thavry et al. 2017). Additionally, the conservation and planting of chiropterophilous plant populations would promote the health and site fidelity of this species (Harbit et al. 2008; Bumrungsri et al. 2013; Acharya 2015b,c; Thavry et al. 2017). To safeguard both the bats and the people who rely on them, sustainable harvesting practices, monitoring programs, and the protection of limestone karst ecosystems are needed (Molur et al. 2002, Furey et al. 2011). Malaysia considers this species to be Near Threatened (Sheema Abdul Aziz, Pers comm 2019).