Tylobolus

In late winter (30 January 2020) after heavy rains, multiple specimens, mainly large immatures and adults, were found in and under rotting oak logs that had been cut from nearby trees and stacked together, and their presence was easily noticeable by the enormous amounts of frass present around and under said logs. No rotting leaves were available, and the logs were surrounded by invasive grasses. Two or three at a time would be found together. No eggs or young were found. Photos below of specimens and habitat.

The same site was revisited in November of the same year, though the area was much drier. Large amounts of dried frass was seen but no specimens were found. In January of 2022 the area was visited again, and around fifteen specimens were discovered under the rotting oak logs that were now quite wet from recent winter rains. A few juveniles and babies were found, but the majority of specimens were adults, some mating pairs, all around 3"/7.62 cm. Interestingly, an atopetholid had been found at the same location a few weeks prior when the area was much drier. Found in Los Angeles County.

On a late morning in early February of 2022, five millipede specimens identified in the field as T. utahensis were found in Zion National Park along the Virgin River under well-rotted cottonwood (Populus sp.) that was very moist to the touch. Three adults measuring about 2.5"-3"/6.35-7.62 cm and two juveniles measuring around 1"/2.54 cm were all found singly under the logs, often in close association with Porcellionides sp., a slug species believed to be a Limacus sp., a large species of springtail, and several species of true spiders. The outside temperature varied between the 40s°F up to the high 60s°F/4°C-20°C.

The substrate was largely composed of very fine river sand mixed with the crumbling wood from the logs, overlaid with fallen Populus leaves. Specimens were usually found amongst the crumbled wood, burrowing into the logs, or half-buried in the sand, all of which were approximately 10-30 yards away from the river itself. One adult specimen was found in another location several miles downstream from where the first two adults and two juveniles were discovered. Multiple logs were found with piles of millipede frass underneath, suggesting this species is quite common along the Virgin River in this area. All specimens either froze in place or immediately went into the classic spiral defensive posture of millipedes, and exuded toxifabricants when further manipulated. They did not move otherwise in the period that photos were taken, though this was likely due to the low temperature slowing their movements.

Tylobolus utahensis specimen, frass, and habitat photos, compliments of Arthroverts (8). Note the composition of the soil the millipedes were found in.