Why do railroads use timber ties on bridges and concrete ones on the ground?

Bug questions! Centipedes, ground beetles, ladybugs and tent caterpillars?

• I'm 18 and over the past couple weeks I've gotten into a "bug" phase. It started after I got a baby tarantula for a pet, and that same night I caught a wolf spider in my basement that I kept. They are both doing very well and I've decided to collect some more insects as 'pets'. I got 6 plastic containers, with lids that close really well and I drilled small air holes around the top. I have 3 small and 3 large, the small measuring 4" tall with a diameter of 4", and the large measuring 5" with a diameter of 5". Two of the small containers are occupied by "Grover", the G. Rosea spiderling, and "Howl", the wolf spider. What I want to put in the other small container is a centipede or two, but I can only find information on the giant varieties or 'house centipedes'. The ones I find around my house are maybe an inch long and brownish-red in colour, and look similar in shape to the giant ones. I live in Ontario, Canada. Does anyone know what they could be, so I can research them for what they eat, etc.? In the larger containers I wanted to use one for ground beetles, one for ladybugs, and one for tent caterpillars. I've done my research on them and know pretty much how to keep the enclosure, and what they eat, but I still have a few questions. How many ground beetles should I keep together, since they might eat each other? I was thinking between 1-3, and they would get a cricket or two three times a week or every second day. Also since they will be in the bigger container, with sticks and leaves to climb on, will they just stay on the ground or will they actually go up in the leaves? If they just stay on the ground, would it be better to just get another small container and keep one alone? The lady bugs will also have lots of sticks and leaves, and I know to feed them moistened raisins or other sweet, non-acidic fruits, and to keep the container a little moist. The container is about a half gallon, so, how many ladybugs could be kept in it? I was thinking between 1-4? For the caterpillars, again, they will have sticks and leaves, etc... how many should I keep in the container? I was thinking between 1-2. Hopefully they would make a cocoon and turn into moths, then I would let them go. Oh, and do they eat only leaves? Which kind of leaves do they like best? That's all my questions for now, hopefully someone can help me out. Oh, and if anyone has any other bugs that might make a neat pet, let me know and I might add one to my collection!

• Answer:

  Ah, a fellow bug lover. Awesome. I like to examine all kinds of bugs (and have owned 20 different species of tarantula). My rule is I never have more than two per container and usually if the bug is a caterpillar I only keep one and feed it until it makes a cocoon, then allow 2 weeks or so for it to emerge as a winged adult, then I wait a day (for the wings to dry) and release it. As for what to feed them, the general rule is you take the leaves off whichever plant you found them on to feed it. It may not eat any other type of leaf. If you have tarantula questions, feel free to email me.