Centipedes are a rough group to identify in North America. The only well-known order, the Scolopendromorpha, was treated by Rowland Shelley in an excellent 2002 monograph (A synopsis of the North American centipedes of the order Scolopendromorpha (Chilopoda)). This was published by the Virginia Museum of Natural History, but is difficult to get ahold of today. (Contact me if you need the PDF, however.) It includes range maps, identification keys, and useful illustrations: a must-have for anyone interested in our centipede fauna.
North America's other two major orders, however, lack such an impressive resource. These are the Lithobiomorpha (stone centipedes) and the Geophilomorpha (the soil centipedes). Today I'll focus on a small section of the Lithobiomorpha, the genus Nadabius.
Nadabius pullus, scale underneath is in millimeters
Before we delve too deep, a primer on important identification characters for stone centipedes. If you're already somewhat familiar with stone centipedes or just want to get to the good part, skip the next paragraph. We've got five major character systems for stone centipedes:
1. Tergital projections
2. Prosternal teeth
3. Antennomere number
4. Processes on ultimate legs (pairs 14 and 15)
5. Leg spurs
Tergital projections refer to the dorsal plates of these centipedes. Their posterior corners are most often rounded, but some centipedes have some posterior corners pointed and projecting posteriorly. This is typically a pretty obvious character. The prosternal teeth refer to the ventral side of the head and are part of the forcipular segment. The stone centipedes have a coxosternite flanked on each side by the forcipules, or venom claws. Along the anterior margin of the coxosternite, between the forcipules, there are two rows of small teeth. The number of these teeth is useful for identification, and are listed in a formula of how many teeth are on each side. 2+2 means there are two teeth on the left and right side of the coxosternite. The antennomere number is exactly what it sounds like: how many segments does the antenna have? Next, males of some genera can have various processes on their ultimate legs (legs 14 and 15). The shape and position of these processes are typically species specific and are very useful in identification. Finally, the number and position of stout spurs distally on each leg podomere are used to separate genera and species. The most common stone centipede family in North America, the Lithobiidae, possess these spurs, while the rarer Henicopidae lack these spurs. The number and size of the leg spurs change as the centipede matures and grows, so juveniles and adults can have different sets of spurs. Make sure you're dealing with a fully mature adult centipede between trying to identify a species!
Okay, so now you know which characters are useful for centipede identification, and that there aren't many identification resources for stone centipedes. What a dilemma! In this post, I'll help you tackle how to identify one of the most common genera in eastern North America: Nadabius.
Nadabius is known from 33 US states and Canadian provinces (Mercurio 2010), see map below. Here in Virginia, I find it almost every time I collect centipedes, no matter the time of year. To quickly separate it from other stone centipedes you might pick up, look for the following combination of characters. If it has all of them, it's Nadabius--though use caution west of the Rocky Mountains, I can't guarantee it applies out there:
Map of the distribution of Nadabius in North America. Shaded states/provinces indicate Nadabius records. Made with SimpleMappr.
Eyes present, antennae typically with 20 articles (may have a few extra, but not more than 23), prosternal teeth 2+2 to 4+4, no tergites with posterior angles produced, last three legpairs with some dorsal spurs, prefemur of ultimate legs with 3 ventral spurs, prefemur of legs 12 and 13 with 3 dorsal spurs, leg 14 tibia with 2 or 3 ventral spurs, leg 15 femur with 2 or 3 dorsal spurs. If male, leg 15 tibia with dorsal crest.
If your centipede has all those characters, congrats! You've got Nadabius. There are 17 species of Nadabius in North America, so let's zoom in just on Virginia because it has a manageable number of species--only two confirmed species for the state! Easily the most common of these is Nadabius pullus (Bollman, 1887). Hoffman (1995) calls it one of the most common stone centipedes in the eastern US, and it's statewide in Virginia. My own collecting confirms his assertion. Our other species is the (much) less common Nadabius aristeus Chamberlin, 1922. It’s recorded from only a handful of Virginia counties: Albemarle, Bath, Highland, Montgomery, Page, and Rockingham. I’ve yet to find it in Montgomery County, despite intense collecting.
Size comparison between Nadabius pullus (left) and Nadabius aristeus (right). Scale is in millimeters.
The two species exhibit a distinct size difference, with the beefier Nadabius aristeus, growing a good deal larger than N. pullus. While Nadabius pullus generally ranges from 8-12 mm long, N. aristeus reaches lengths of 13-18 mm (lengths based on measurements of specimens I've collected). Nadabius aristeus can easily be twice as large as N. pullus, and this size difference easily distinguishes the two. Additionally, Nadabius aristeus has 3+3 prosternal teeth (typical for specimens that aren't fully mature) or 4+4 prosternal teeth instead of the 2+2 prosternal teeth that N. pullus has. Both species have an accessory claw on the ultimate legs, meaning there’s a smaller claw at the base of the large claw at the end of the leg—look carefully from multiple angles and backlight the specimen if necessary.
Ventral view of Nadabius pullus head: note the 2+2 prosternal teeth arrangement.
Ventral view of Nadabius aristeus head: note the 4+4 prosternal teeth arrangement.
Another helpful character for species identification of Nadabius is found on the ultimate legs (leg pair 15). Adult males have a dorsal process on each ultimate tibia which varies in shape according to species. In N. pullus, the process is a low ridge which is weakly differentiated from the rest of the tibia. It can be easy to miss, so look for the many setae that accompany the ridge. It will be on the mesal (inner) corner of the tibia.
Ultimate legs of Nadabius pullus: note the slightly raised dorsal process and its associated setae.
Nadabius aristeus also has a dorsal process, but it is more obvious. The process is horn-like with a rounded tip, and is positioned more on the midline of the tibia. It also has associated setae.
Ultimate legs of Nadabius aristeus: note the horn-like dorsal process and its associated thin setae.
If you weren’t tipped off by the size of the centipede, checking out these additional characters clinches the ID. It’s refreshing to find nice, obvious characters separating stone centipede species, so we’ll take the win here. Elsewhere in North America, there are additional Nadabius species, so identification may get trickier—be wary! If you want to explore those other species, check out the references below. Chamberlin’s 1922 paper is especially useful.
References:
Chamberlin RV (1922) Further studies on North American Lithobiidae. Bulletin of the Museum of Comparative Zoology at Harvard College 57: 257–382.
Hoffman RL (1995) The centipeds (Chilopoda) of Virginia: a first list. Banisteria 5: 20–32.
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.
Shelley RM (2002) A synopsis of the North American centipedes of the order Scolopendromorpha (Chilopoda). Virginia Museum of Natural History Memoir 5: 1–108.