|MadSci Network: Zoology|
You have asked several interesting questions:
Great discussion of sleep in invertebrates by Kelleen Flaherty
Sleep in bees - see discussion added at the bottom of the page
For mantids, defence while "sleeping" is probably not much of an issue. When they are awake, their normal method of defence is camouflage and remaining still. They can continue to do this in their sleep.
I have found mantids, which I have disturbed, to respond in two ways:
1)They fixate their eyes on me and track my movements
2) They start walking away
Even when mantids do move because they are disturbed, they seem to avoid flying, which is an energy-demanding activity. My point here is that mantids do not need to warm themselves up to same extent as insects that regularly use flight to avoid predators.
I have observed butterflies, which I disturbed, to spend time warming themselves up before take-off. This is a time of vulnerability. For this reason, remaining motionless and camouflage are some of the best strategies used by insects to avoid predators.
In any case, mantids probably sleep at night when they cannot hunt for food. A resting mantis would probably not have any predators during this time. Only if they are flying would they be preyed upon by bats and an ear has been found in at least one species that enables them to detect a bat's echolocation system.
Mantids have formidable spines on their forelegs that they use for grasping prey. To some extent, these can be used to protect themselves against predators. You will soon find out about these spines if you handle your mantis carelessly.
Around the world, mantids provide some of the most spectacular forms of camouflage in the animal kingdom. They have many other fascinating attributes and I think you will enjoy watching them.
Try the links in the MadSci Library for more information on Zoology.