Please ID This

Well, I can't tell you what species of millipede it is but they pretty much all eat the same stuff: rotting leaves, white rotted wood and other composing plant matter. So if you've got a forest close by, dig for the layer of last year's leaves, mix it with crumbled white-rot wood, some dirt, maybe a little sand if the dirt is mostly clay and crushed eggshells for extra calcium. Pile that mix a good 10inches high, millipedes live mostly underground. You can offer pieces of peeled fruit and vegetables as a little snack on the side, but the main food is the compost-rotted wood mix. As millipedes like a little protein every now and then you can put a small bowl of dry cat food or fish flakes in the terrarium too.
Have fun, they're pretty interesting "pets".

Hello,

The chrushed cocnut substrate, the sphagnum moss and the repti bark are not siutable for millipedes, in worst case it can kill the animals if they didn´t have to eat enough... I think it would be the best for your millipedes, if you go to the next forest and collect some white rot wood and rotten leafes. Stef had already explain it Maby you can look at the homepage (the button left, above "i Diplopoda.de") an translate it with google. This should answer all your questions.

Greez, Beni

If you wanna kill them slowly and cruelly cocos fiber is the way to go. It has no nutritional value to the animals and seems to clog their digestive tract so they'll eventually starve. Most of the stuff for reptiles, especially the sphagnum are treated with chemicals to make them "look better", millipedes will at least nibble on everything they come across and see if it's eatable, the preservatives in sphagnum could be toxic. Reptid bark is cedar and pine, right? You don't wanna give them wood/bark/needles from plants with a high content of essential oils either, those are toxic to most animals, not just millipedes.

If you don't have a forest nearby, what is the next best source of pesticide-free dirt? You can try with a mix of compost and fertilizer- and peat-free flower dirt, maybe mix some hay under (but be careful, that gets moldy pretty quickly, no troubles for the millipedes, but not healthy for you to breathe in). I can't see a substitute for the rotted wood though, they need the fungus they find in the rotted wood for digestion and well-being. If the animals were caught somewhere near you, go with your brother and check where he found them and check what they could have eaten, take some of that home. During the day they often hide under wet wood, even if you don't have a forest, check if there's any dead trees around or branches that are rotting, get them some of that. White rot is the soft-squishy wood pulp, there's also red rot which makes the wood hard and break in small cubes, that won't work, you need the soft crumbling white stuff.

Repti bark is made of Douglas fir, so u will have the same side effects as using cedar or pine.

Listen, the most common belief is that millipedes just feed veggies and other stuff u throw on the surface, fact is that they feed almost on the substrate, so if u wanna keep them healty, here we go:

A nutrient-rich substrate is very important for successful keeping and reproduction of tropical millipedes.
Expensive substrat mixes and soil substrates for keeping reptiles are not suitable because of their lean soil composition; bark mulch of pine trees is totally unsuitable by the resins contained therein.
You can assemble an appropriate substrate very low-cost effective by combining the following ingredients, just mix yourself:
• 3 parts unfertilized seed compost (aka forest soil, humus from the top soil of deciduous forests)
• 2 parts rotted leaves from the previous year, preferably hardwoods such as oak and beech (please make sure that this is not nearby busy roads or is sprayed with insecticides against Thaumetopoea processionea in several forest areas, if in doubt, don´t hesitate to ask the forestry department).
• 2 parts shredded decayed wood /deadwood. This is the target stage, if it feels a bit like a sponge and could be crumbled easily with your fingers. (It is often found along rivers as flotsam and can be taken free of charge).
• 1 part sand to attempt a loosening of the soil. You can use the cheapest bird sand from the drugstore, it usually containes anise oil but anyway; this is highly volatile and will not affect the animals.
• 1 / 2 part grounded cuttlebone, which is important as it provides calcium carbonate for the development of exoskeleton, alternatively: granulated slaked lime for gardening. If larger quantities of the substrat should be produced, this is a very affordable alternative.You can also mix small crushed eggshells under the substrate.

Edit:

Don't get confused bout the spaghnum moss, its often jumbled with island moss (cetraria islandica) which is also offered for terrariums. Compared to real sphagnum, island moss is often prepared with dye and varnish to preserve it, so do not use this one.
Sphagnum moss to preserve a humidity is ok, but in my opinion its very expensive.

And according to the ID of ur species; it would be helpful if we get some information where u found this (Location)

Greez,
Shura and the whole bunch

Seems I got it:

Yosemite Millipede (C. yosemitensis) - Californiulus yosemitensis

Greez,
Shura and the whole bunch