Phosphaenus hemipterus is a flightless glow-worm with a widespread distribution across Europe. We assign it to the category of Least Concern, based on its wide distribution, broad habitat use, diurnal activity, and use of pheromones rather than light-based courtship signals.

Phosphaenus hemipterus has a widespread distribution across Europe. From the Iberian Peninsula it occurs in mid to northern Portugal and northern Spain. In central Europe it is found from southern England, France, Belgium, the Netherlands, Germany, Poland, Switzerland, northern Italy, Austria, Hungary, Slovenia, Croatia, Slovakia, Serbia, Bulgaria and Romania. In Fennoscandia this species is known from the south of Finland and Sweden, including Gotland, although it is apparently absent from Norway. It is also known from Lithuania, Estonia and Latvia, and the most easterly known distribution is near Moscow in western Russia. Phosphaenus hemipterus was discovered in 1947 in Halifax, Nova Scotia, presumably introduced in soil of nursery plants, and several populations were reportedly still thriving in this vicinity in 2009 (Majka and MacIvor 2009). These authors also mention the species from Crete but do not give any reference and its presence on this island seems rather unlikely.

At present there are no studies that have investigated the population size or trends of this species.

Phosphaenus hemipterus is unusual among glow-worm lampyrids in that adults of both sexes are flightless. Although adults are weakly bioluminescent from a paired light organ (in the last segment inherited from the larval stage), their daytime activity and small size (male body length ~10 mm) makes them easy to overlook (De Cock 2000).

Larvae are often found in leaf litter in woodland or dense vegetation, particularly on the edges of more open habitat (De Cock 2000, De Cock et al. 2009). Larvae are nocturnally active and glow spontaneously. Phosphaenus hemipterus larvae are obligate earthworm predators (Majka and MacIvor 2009), unlike most firefly larvae, with larval habitat preferences matching those of their earthworm prey. Pupation takes place in April-May and the pupal stage lasts for approximately ten days with adults emerging from late May/early June (De Cock et al. 2009).

Phosphaenus hemipterus adults are most abundant in June and early July (Teofilova et al. 2021), although they are occasionally collected from late July to August (Burakowski 2003) and even September (Magis 1977, Teofilova et al. 2021). Adults of both sexes are flightless (Novak 2018, De Cock et al. 2009), a life history trait that limits their dispersal ability. Most records of adults come from human-constructed habitats such as gardens, parks, and churchyards (De Cock et al. 2009), but Phosphaenus hemipterus is also found in orchards, field edges, and hedgerows (Teofilova et al. 2021). They typically occur in areas with compact, loamy, or clayey soils (De Cock 2000, De Cock et al. 2009). It is thought that Phosphaenus hemipterus prefers cooler and wetter conditions than the common glow-worm Lampyris noctiluca. Males are diurnal, and are often found on vegetation (Burakowski 2003); they also congregate near walls or paving stones (Magis 1977, De Cock et al. 2009). Females stay in leaf litter or lower parts of plants and are thought to be active mainly at dusk (De Cock 2000). Adults have vestigial mouthparts and do not feed (De Cock et al. 2009), with adult life span ranging from 12 to 23 days for females (De Cock et al. 2009).

Phosphaenus hemipterus adults of both sexes are weakly bioluminescent in response to disturbance (De Cock 2000, Majka and MacIvor 2009), but do not appear to use their bioluminescence in courtship. Instead, females use pheromones to attract males; field experiments show that males can use these airborne scents to find a female located at least 20 metres upwind (De Cock and Matthysen 2005).

Mated females lay eggs in batches of 60 to 120 in late summer. Larvae overwinter in small groups and become active again in early spring (De Cock et al. 2009). The life cycle of Phosphaenus hemipterus lasts two to three years (Novak 2018).

The occurrence of this species within many human-constructed habitats (gardens, parks, churchyards) suggests they are not currently threatened by habitat loss. However, the poor dispersal ability of these flightless glow-worms suggests that habitat fragmentation will cause isolation of local populations (Teofilova et al. 2020), making them prone to extirpation through stochastic events such as development or site clearance. Males of Phosphaenus hemipterus are often found on or near walls and paths, which in urban areas are often treated with herbicides that may have a detrimental effect on glow-worms (Lewis et al. 2020). The use of herbicides and pesticides could also affect the availability of earthworms, the primary prey for the larvae of Phosphaenus hemipterus (Pelosi et al. 2014). Similarly, the presence of non-native flatworm species such as the New Zealand flatworm (Arthurdendyus triangulatus) will have a major impact on the availability of earthworms (Thunnissen et al. 2022).

Since Phosphaenus hemipterus adults are diurnally active (females have been found at environmental light intensities from 0.5 to 2,000 lux) and females use pheromones to attract males (De Cock 2000, De Cock and Matthyson 2005), light pollution is not likely to interfere with sexual communication in this species. However, as for other terrestrial taxa, artificial light has the potential to cause temporal disorientation by disrupting the internal timekeeping mechanisms that regulate daily and seasonal rhythms of activity (Gaston et al. 2017) and we have no idea yet about the effects of artificial light on the nocturnal larval behaviour and development.

There are no documented uses of this species in trade, medicine, or entomo-tourism.

Land use changes, for example property development and land clearance, are likely to be particularly damaging for Phosphaenus hemipterus, either due to destruction of their breeding sites or by fragmenting remaining habitat. The use of pesticides on sites where this species occurs should be avoided.

This species may occur on regionally protected sites, and management of such sites should take the habitat requirements of this species into account. Consideration should be given to providing protection to other sites where this species occurs.

This species appears to readily colonise new sites where it has been introduced (Majka and MacIvor 2009, De Cock et al. 2009). This suggests that conservation translocations could be used to establish or reintroduce populations to sites however this should only be considered as a mitigation option of last resort for development projects.

Increased efforts are required to control or eradicate existing populations of non-native flatworm species and to prevent the establishment of new populations of these species.