Soil centipedes are stringy little noodles come to life. Thin and wispy, they’re well-adapted to a life spent in the soil. They mostly go unnoticed--unless you’re a gardener or entomologist. Sadly, they’re not the most aesthetically pleasing centipedes, and here in the eastern United States, range from pale yellow to scarlet red.
Geophilus cayugae on the underside of a small rock I unearthed from the top of a streambank.
The most common soil centipede genera I find are Arctogeophilus (Geophilidae) and Strigamia (Linotaeniidae), but the uncommon genus Geophilus (Geophilidae) sometimes makes an appearance. I still don’t have many specimens of Geophilus, but I have enough now that I’ve identified three species on the mountain. One is rare, but easy to identify: Geophilus vittatus. All you need to do is look at its back: it has dark diamond-shaped markings. Do you have a specimen of Geophilus? Does it have those diamond markings? Boom, piece of cake. Don’t look a gift horse in the mouth when it gives you an easily identifiable centipede, just pass it some oats and say thanks.
This centipede is the rare geophilomorph with a common name: the diamondback soil centipede. Crabill (1954) reported finding this species most frequently under loose bark, and Hoffman (1995) states it can be found under loose bark flakes of loblolly pine (Pinus taeda), which may explain why I don’t often find it. Usually I’m more focused on the leaf litter rather than peeling bark. Interestingly enough, Crabill also reported that G. vittatus is the most common geophilomorph other than the scarlet red Strigamia bothriopus in the Ithaca, New York area. A quick perusal of photos on iNaturalist for the Ithaca area seems to corroborate this. Incidentally, my collections of this species represent a new county record for this centipede in Virginia, neat!
Geophilus vittatus on my hand. Typically, Geophilus species grow to about an inch and a half long.
The other two species I’ve found on the mountain are Geophilus cayugae and Geophilus varians. Geophilus cayugae is a rare find, while G. varians is common. Sadly, these species aren’t quite as simple to identify as G. vittatus. But with the power of side by side comparison, it’s not too difficult.
Geophilus cayugae (left) and Geophilus varians (right) under the microscope. Note that the two images are not at the same scale. This specimen of G. cayugae is 51 mm long, while the G. varians specimen is 28 mm long.
Both G. cayugae and G. varians are yellow centipedes with orange-red heads, a common color pattern for soil centipedes. They're distinguished from other Geophilus species in the eastern US by having lateral coxopleural pores, 57-67 pairs of legs, and a concealed prebasal plate. The two species are differentiated by the following characters: Geophilus varians has unsclerotized paxilli and sacculi and very long ultimate legs, while G. cayugae has sclerotized paxilli and sacculi (though the sacculi are small) and does not have very long ultimate legs. The simplest character that separates these species is the length of the ultimate legs, which Crabill illustrated (see image below).
Crabill’s illustrations are pretty good, but it’s still a bit difficult to jump from the illustrations to actual specimens. Subjective character comparisons like long/short vary in their usefulness, but are almost always murky until you’ve seen the characters yourself.
Comparison of ultimate leg length in Geophilus cayugae and Geophilus varians.
This is better: now we can see both the length of the preceding legs and the length of the ultimate legs for each species. In Geophilus cayugae, the ultimate legs are about 1.5x longer than the preceding legs. But in G. varians, the ultimate legs are much longer: about 2.5x longer than the preceding legs. In these particular specimens, the ultimate legs are also thicker, but this is because they’re both adult males. In the adult females, the ultimate legs are slender and not much thicker than the preceding legs.
In this ventrolateral view of Geophilus cayugae, you can see the lateral coxopleural pores of the species pretty well. This character is shared by G. varians, but not by some other Geophilus species, such as G. vittatus.
Ventrolateral view, ultimate legs of Geophilus cayugae.
This next photo shows a dorsal view of the ultimate legs of Geophilus varians, and it’s immediately noticeable how much longer they are than the preceding legs.
Dorsal view, ultimate legs of Geophilus varians.
In terms of body length, all three of these Geophilus species grow to about the same size. Geophilus varians tends to be the smallest, with average lengths of 30-35 mm, but it can reach 40 mm long. Geophilus vittatus is typically 25-40 mm long, but can grow to 52 mm in length. Geophilus cayugae also averages between 25-40 mm long, but reaches 68 mm at its longest. However, measuring soil centipedes is a difficult task, as they can stretch and compress, telescoping their body. It’s slightly easier to measure them when they’re dead, but alcohol preservation and the position they die in can also affect their length. Altogether, body length isn’t useful for species ID for these species.
Leg number might be useful for separating Geophilus cayugae and G. varians, at least in the Blacksburg area. The specimens I’ve collected of G. varians have 55-59 leg pairs, though one specimen from Augusta County, Virginia has 63. My specimens of G. cayugae, on the other hand, have 61-65 leg pairs. I wouldn’t trust leg number all on its own, but it may be a useful hint based on my localized collecting.
Geophilus varians is widespread in Virginia (see map below), with records stretching from Tazewell County east to Greensville County (Hoffman 1995). It’s certainly the most common Geophilus species I find, and has a large range in the rest of the US as well, ranging from Michigan to South Carolina (Mercurio 2010).
Finding Geophilus cayugae is a bit more interesting, as it’s a rare species not only in Virginia, but in the eastern US (except for around Ithaca, New York, according to Crabill). Aside from its type locality in Ithaca, it’s reported from only a few mountaintops in Virginia, North Carolina, and Tennessee. My find represents a new county record (yellow on below map), and at 701 m, it’s a slightly lower elevation—Hoffman mentions the montane-boreal habitats of this species being all above 1000 m in Virginia. It may be that G. cayugae is more active in the winter when temperatures are cooler, a preference catered to by its mountaintop habitats. I found a specimen last week (January), at a time when parts of the leaf litter and soil were still frozen. I’ve also found the species in Wood County, West Virginia (a new state record!) in December, so the chillier months seem to be the time to look for G. cayugae.
View of a forest near Blacksburg, Virginia in late fall. Photo taken in November 2022.
Wintertime collecting doesn’t have to be dreary: it’s one of my favorite times to collect myriapods. You run into fewer people, the mosquitoes aren’t out (but still be way of ticks), and there’s plenty of leaf litter habitat around. Plus, wearing extra layers gives you more pockets to store bug vials in. It’s a great opportunity to find species you don’t run into during the warmer months, and you never know what cool centipede you’ll find digging around the duff in January.
Wintertime forest near Blacksburg, Virginia. Photo taken in late January 2023.
References:
Crabill RE (1954) A conspectus of the northeastern North American species of Geophilus (Chilopoda, Geophilomorpha, Geophilidae). Proceedings of the Entomological Society of Washington 56: 172–188. https://www.biodiversitylibrary.org/page/16179233
Hoffman RL (1995) The centipeds (Chilopoda) of Virginia: a first list. Banisteria 5: 20–32. https://www.biodiversitylibrary.org/page/58632363
Mercurio RJ (2010) An Annotated Catalog of Centipedes (Chilopoda) From the United States of America, Canada and Greenland (1758-2008). Xlibris, United States of America, 560 pp.