Green Thumb Tanks

Narceus americanus/annularis species complex, Giant Pinkleg, Worm Millipede, Giant Millipede, Iron Worm

Classification

Class Diplopoda (Millipedes), Order Spirobolida (Round-backed Millipedes), Family Spirobolidae. While the species classification is Narceus americanus, it is likely that there are many species included under the name. All are very similar and this care sheet should apply to any of them.

Dangers

None serious. While many species of millipedes secrete a variety of defensive compounds ranging in effect from dying one’s hands unfortunate colors to cyanide poison, the American Giant just likes to curl up tight when threatened. It is capable of releasing a fluid that smells mildly gross and might stain skin for a day, but this is documented rarely and I have never experienced it. If your millipede objects to handling in this way, simple handwashing should take care of it. As always, do not touch your eyes.

Appearance

One of the biggest millipede species native to North America, American Giants can reach lengths of four inches and tend to be dark brown with light brown, almost orange segmentation. Like all millipedes they have two pairs of legs per segment. The legs are generally orange-brown, occasionally light enough to justify the common name of American Pinkleg. Rarely an albino form can be found among hobbyists, which is brilliant because lack of pigmentation is an incredibly rare condition among invertebrate species.

Life Cycle

American Giants breed late spring or early summer and mate many times in a season. In captivity they seem to be able to breed year round. Some sources suggest that females lay eggs singly, but American Giants will still lay many eggs overall. The hatchlings will have just a few segments and six legs, and will add to their body plan with each molt. There are reports of American Giants living ten years in captivity, but lifespan probably varies with diet nutrition and whether they were wild caught.

Environment

American Giants live in fairly humid, generally warm areas of the United States, usually in forests and woodlands with lots of leaf litter. They are found under logs and rocks or beneath leaf mulch. The geographic range portrayed below is based off of bugguide.net and animaldiversity.org.

Housing

American Giants are (as the name asserts) giants among North American species, so they require more space then some other millipede species such as Scarlets or Bumblebee ‘pedes. They are shrimp compared to Sonoran Giants though, so if you are looking for a massive beast, check out the care sheet for Orthoporus ornatus. Speaking of which, if you want a millie that is truly thiccc with three c’s, check out Narceus gordanus, the Smoky Oak Millipede. Required enclosure space is still very minimal, however. Since they are not enthusiastic climbers and spend all their time either on the ground or in the ground, they don’t need be given much space vertically. Depth of substrate is important because it will change how easily the substrate can be kept moist. The deeper the substrate is, the more slowly it will dry out, especially the lower layers. A rule of thumb that isn’t really based in anything except convenience and guesstimation is to allow about a quart of substrate per millipede. More is always better, especially since it will take more time to use up the substrate in larger enclosures. So, for a group of up to six I like to take a plastic shoebox (which is about six quarts) and fill it up with four or five quarts of substrate. These bins have a nice snap-on lid, but if your setup does not have a top you should be sure that the distance from the surface of the soil to the top of the enclosure is greater than the adult length of the millipedes so they don’t escape. If you find that the enclosure is muddy or grows mold within hours, use a drill (easy) or a hot nail (less easy) to make small ventilation holes in the lid or around the top edge of the bin.

Substrate is key to millipede care. The best substrate will contain decomposing hardwood and leaf mulch. Softwood (evergreens such as pines) contain anti-invertebrate resins and should be avoided. If in doubt, use oak. I like to use a mixture beetle keepers call flake soil, which is made by allowing chunks of oak or other hardwood to compost until the particles are on average a quarter inch or less. I add leaf mulch, which is crushed hardwood leaves, and a couple large rotting pieces of oak. Add leaf mulch whenever it seems be depleted. Coconut coir is readily available at pet supply stores and can certainly be used, but should be mixed with leaf mulch and wood chunks just like flake soil, and is probably less edible for the millipede. The soil itself should stay nutritious for a long time, but when it looks entirely like millipede poo and no more wood fiber is visible, get a new batch of substrate ready. Be sure to check the old substrate for babies! Millipede frass is excellent compost and can be added to gardening soil or used to jumpstart flake soil if you make your own, by the way.

Keep the substrate moist! Millipedes dry out easily, which is why they are most commonly found in damp areas. Check the dampness by sticking your finger into the substrate occasionally. It should be dry enough that it isn’t mud, but damp enough that some sticks to your finger. Pour a little water down the side whenever it feels like it is becoming dry and your ‘pedes should be happy.

Millipedes like it warm, and the American Giants are no exception. However, they are not as particular as some tropical species. Room temperature (70-75f) is just about right for these guys. If your house is cooler than that you should provide a heat source. Do not use a heat bulb as these tend to produce too much heat and dry both substrate and millipedes right up. A small heat pad should do the trick, but should be placed on the side of the enclosure above the substrate so as to avoid drying out the substrate. With my shoebox setups, which are mostly substrate and very little open space, I place heat pads on the lid if I need them. Heat pads should not be placed in the traditional location of under the tank because millipedes naturally burrow down to cool off, and might cook themselves trying to escape the heat by inadvertently moving closer to the heat source. Providing heat on the side allows them to self regulate their temperature by moving deeper or higher.

NOTE: Many people online insist that millipedes need high humidity (air moisture). This is not true for all species, and can encourage mold growth. The more important aspect is soil moisture, which can be maintained more easily by keeping high humidity in the enclosure, but the two are not the same. Humidity may be important in keeping some tropical species, but is less important for the temperate American Giant Millipede, as long as soil remains moist.

Feeding

Housing and feeding are very closely related for all millipedes since millipedes are detritovores, meaning that they eat leaf mulch, rotting wood, and whatever fruits and veggies they might luck into. This means that their substrate is also their food and is very important to their health. In addition to providing a tasty substrate as previously described, American Giants enjoy soft fruits, vegetables, and mushrooms. If you offer these on the surface, they will often be enticed from their hiding places. Banana slices are a good choice, but they will eat most non-meat table scraps, including: lettuce, spinach, carrot, potato, cucumber, apple, and mushrooms. Be careful not to feed too much of these at a time to avoid mold. Large groups of American Giants can eat a lot of fruit at a time, but for individuals or pairs it is best to start with a small slice or chunk. A good rule of thumb is to feed whatever can be eaten in the space of a day. If food begins to mold, remove it and throw it away. I have a designated plastic “dirt spoon” I use to mix substrate and scoop mold for all my invertebrate enclosures. American Giant Millies also enjoy dry dog food and tropical fish flakes.

NOTE: Many sources out there insist that millipedes absolutely need a calcium source mixed into their substrate. However, I do not believe there is any empirical evidence that the addition of calcium powder, eggshells, or cuttlebone to a millipede’s diet is crucial to their survival, especially when given a varied diet. There is also no evidence I’m aware of that this negatively affects millipede health, so if you feel safer adding calcium supplements by all means go for it.

Breeding

If all the conditions of care are met, breeding is as simple as having a male and a female. Males will solicit females by walking back and forth along their backs. Some males may be able to produce silk in conjunction with pheromones, which is just crazy. If the female is receptive they will both rear up and intertwine to line up their genitals. Males can be identified with patience and luck. Their seventh segment will look like it is missing legs because its appendages there are modified to take a packet of sperm (called a spermatophore, if you need a dinner topic) and place it into the female during mating. Females lay eggs in small chambers provisioned with leaf mulch in the substrate. Millipede babies hatch with six legs, but quickly grow and shed their skins. With each molt they will add new segments and legs to their length. Care of babies is identical to that of adults, with the exception that they will likely not come out of the substrate until they are juveniles, so substrate quality is even more important to their care.

Preservation

Deceased specimens can be preserved in alcohol, such as ethanol, in a manner similar to spiders. Millipedes should not be pinned, but American Giant Millipedes have a thick enough exoskeleton that they can be dried and displayed in a Riker mount, although they often lose their coloration. Freeze drying may help to retain true to life coloring.