Former records of this species from outside of Finland were found to refer to another species, Hylochares populi (Brüstle and Muona 2009).

The present taxonomic status of Hylochares cruentatus sensu Brüstle and Muona (2009) appears dubious. Eucnemids are known as generalists regarding tree species suitable for larval development, there is no obvious genetic distance between the Finnish population of Hylochares cruentatus and Karelian population of H. populi (both sensu Brüstle and Muona (2009)), the morphological differences are weak and within the morphological variability grade of a single species.

This species is a specialist of small, bushy willows Salix myrsinifolia and S. pentandra, a rare habitat in south Finland. It uses small diameter, dead branches and trunks. The actual known distribution is very limited in the south of Finland while another population nearby is considered extinct. The extent of occurrence (EOO = 1,650 km²) and area of occupancy (AOO, is at present ~20 km²) qualify for the Endangered (EN) category. However, the species is suspected to be more widely distributed as it is poorly known and hard to find, but even if more localities are found the EOO and AOO are not expected to exceed the thresholds for Vulnerable under criterion B. It is unclear how the population is fragmented or not, but it is likely that it is considering its occurrence around Finland's capital. It occurs at no more than 10 locations. The main threat to the species is the cleaning of small rivers and the limitation of natural floods which reduces the availability of the host trees, causing continuing declines in the quality of its habitat. It is therefore assessed as Vulnerable B1ab(iii)+B2ab(iii). Further taxonomic study is needed to confirm the taxonomic status of this taxon.

Hylochares cruentatus is a European endemic species, at present only known in southern Finland according to the taxonomic revision of Brüstle and Muona (2009). All former records from other areas refer to Hylochares populi (Brüstle and Muona 2009). The species was only known from a handful of specimens, found before and during the 1950's and was therefore considered Regionally Extinct (RE) until recently. Records shown by the Finnish Species Information Center (LAJI.FI 2021) for this species show a small number of scattered old (1920 or older) records to the north of Turku, with more recent records (circa 2006 onwards) around Helsinki.

The species is not present in Estonia (it was erroneously listed for this country; U. Roosileht pers. comm. 2023).

This is a very rare species. However, as a small beetle bound to a specific habitat it is likely under-recorded and under-sampled. It was considered extinct for a period of over 50 years until a small subpopulation was rediscovered near Helsinki (Muona and Brüstle 2008, Brüstle and Muona 2009). Several adults and larvae were observed there recently. The quantitative size and trend of the population are unknown.

This is an obligate saproxylic species found in the southern boreal zone (E. Hyvärinen pers. comm. 2009). Observations by Muona and Brüstle (2008) and Brüstle and Muona (2009) demonstrated that "Hylochares cruentatus breed in hardwood of large Salix bushes and trees in Finland. Salix myrsinifolia and S. pentandra are the only host-species. All affected trunks had a broken top. Smaller trunks were attacked on a low height, usually less than half a meter from the ground. The first eggs were laid singly on surface wood, probably on damaged spots. After the first beetles had emerged and mated, eggs were often laid in the walls of old adult burrows. This way of laying the eggs close to the old site seemed to be a strategy for utilizing the limited area suitable for the larvae. It resulted in the characteristic groups of emergency holes observed, including the groups of holes appearing yearly at the same spot. After a few years the breeding sites close to the ground turn too soft for the beetle. In the few cases when the beetle had invaded a huge trunk or a tall stump, the amount of suitable wood appeared to be larger than in the small trees as emergence holes were found along substantial stretches of the trunk. However, even in these cases local aggregations could be seen. Adults emerged between June 1^st and June 24^th during the three study years."

Mating "was observed immediately after the emergence. Males were seen for about a week, after which only ovipositing females could be observed. Nearly all the breeding sites were on the banks of the regularly flooding small river that dominates the site, but a few appeared to be on permanently dry land some 20 m from the river. Inundation of the host tree base might be essential for the infestations, but it is also a feature typical of the habitat of S. myrsinifolia. Suitable appearing trunks of Salix caprea, L. Salix x rubens Schrank, Populus tremula, Alnus spp. and Betula spp. were studied without success. Clearly, they did not suit the beetle the way the two willow species did." (Brüstle and Muona 2009).

The species appears to avoid Salix caprea, the most common tree-sized willow in southern Finland (Brüstle and Muona 2009).

It is unlikely that Hylochares cruentatus is seriously threatened by human activity nowadays. However, the favoured habitat - small streams regularly overflowing with long continuum of small, bushy willows (Salix myrsinifolia, S. pentandra) - is rare in southern Finland and formerly have been dredged and drained. Moreover, seasonal flooding is being discouraged while densely growing willows on banks are cleaned off (Brüstle and Muona 2009). The population density appears low to very low and the Finish population appears fragmented, which requires further confirmation and should not be considered the main threat at this moment. However, the species is likely at least moderately good flyer able to (re)colonise new suitable habitats.

It is used for scientific research.

Hylochares cruentatus is a specialised lignicolous beetle which is endemic to Finland and consequently must have high national conservation priority. The species has been assessed as Endangered (B1ab(iii)+2ab(iii)) on the Finish national Red List (Hyvärinen et al. 2019). Suitable habitats should be mapped and controlled (Brüstle and Muona 2009). The recently discovered Finnish population has been given protection by the establishment of a protected area (E. Hyvärinen pers. comm. 2009). Habitat restoration and site management are recommended to ensure that this species' habitats are well managed and not drained, and further taxonomic studies are needed to confirm the identity of this taxon concerning subpopulations formerly assigned to this species.