Hello,
I'm not entirely certain that the animal you are using is a maggot. Just so you know, maggot is the name give to an immature fly. A grub is an immature beetle. You may even be using a kind of worm. Maggots, grubs, and worms tend to spend their time in dark, damp places. All three kinds of animal would likely choose that chamber in your experiment, so I think I can answer your question assuming it is one of these.
Movement stimulated by light is called phototaxis. (Photo is light and taxis is movement.)
There are two main reasons for maggots to prefer darkness. The first reason is that dark places tend to be damp also. An animal prefering damp places may use phototaxis to get there. So why else would a maggot prefer darkness? Because without light, it's hard to see. Many animals that are hunted prefer darkness. If a grub, maggot, or worm were to crawl on the open ground, it would be quickly snapped up my a bird as a tastey snack.
Movement stimulated by water is called hydrotaxis (Hydro is water and taxis is movement.) Hydrotaxis is a kind of chemotaxis. (Chemo is chemical; water is a kind of chemical.)
There are two main reasons for a maggot to prefer dampness. The first, and most important reason is that water prevents them from drying out. Maggots (and grubs and worms) have soft bodies that can easily dehydrate. These animals are very sensitive to changes in moisture; without moisture they dry up and die. The second reason why maggots like moisture is that they prefer moist food. Many maggot feed on decaying vegetation. Without moisture to support bacteria and fungi, a pile of grass will not break down enough for the maggots to eat it.
Thank you for your question, I hope this information is of help to you.
I also recommend reading this MAD Scientist essay by Rob Campell that further explains taxis in insects.
John Carlson
MAD Entomologist
