Identification of beetle larvae is always not an easy job. This common species from early decay stages of white spruce deadwood has been identified as a sap beetle larva (family Nitidulidae) in my species list. However, I realized that this is a larva of Rhizophagus spp. (family Monotomidae) after careful re-identification (Fig. 5). I believe it is probably Rhizophagus dimidiatus Mannerheim, because 99% of adult Rhizophagus spp. in my collections was R. dimidiatus among three Rhizophagus spp. (R. dimidiatus, R. brunneus, and R. remotus).
The most important character that separates Monotomidae from other cucujoid groups (e.g., Nitidulidae) is the presence of ‘ventral epicranial ridge‘, which is shown in Fig. 5.
*Please click the photos if you’d like to see the enlarged images.
Fig. 1. Rhizophagus dimidiatus (Dorsal view)
Fig. 2. Rhizophagus dimidiatus (Lateral view)
Fig. 3. Rhizophagus dimidiatus (The forked urogomphi are important character, lateral view).
Fig. 4. Rhizophagus dimidiatus (Head and thorax, dorsal view)
Fig. 5. Rhizophagus dimidiatus (The presence of ventral epicranial ridge is the most important character that separates the family, Monotomidae from other closely related beetle families, ventral view).
Fig. 6. Rhizophagus dimidiatus (Larva and adult, dorsal view)
Beetles in Deadwood 