Preying mantis are carnivorous insects which consequently require live insects of a suitable size to feed upon. Unlike some other invertebrates kept in captivity like tarantulas, most mantids have a very healthy appetite and will feed in a daily basis.
Mantids will typically eat insects up to around half their body length though a few may tackle anything up to their own size. For safety though the smaller insects are less likely to put up a fight when caught and so are less likely to damage your mantis.
Whilst virtually any live insect has potential as a food source for your preying mantis, I have found that anything which rests *off* the ground works best. For example, most mantids rest in bushes and trees in the wild, waiting for a meal. Staying off the ground is a safer option because they are away from ground-swelling predators like rodents which love nothing more than tucking into a juicy mantis.
The problem with some forms of livefood like crickets is that they typically stay on the ground, while your mantis will be up high. So your mantis may not see the prey on the floor of the cage or may not want to move down to ground level to try and catch up.
Personally I have therefore found insects that will move up – either climbing or flying – may prove a more readily-accepted form of prey for a mantis.
For tiny mantids fruitflies (Drosophila) prove a better food source than pinhead crickets for example, while many larger specimens will often enjoy some juicy flies.
This needn’t be as hard as you may imagine. One can visit a fishing shop to buy some (unbleached) maggots which can then be kept in the refrigerator to slow down their growth. These maggots (or “gentles”) are typically almost ready to pupate into adult flies which makes life very easy.
When you are ready to keep your mantis you can simply remove some maggots from the fridge and place them in a small tub with a little sawdust. Normally within 24-48 hours they will start to pupate into small brown pupae that look rather like guinea pig faeces. You can then simply drop these into your mantis cage and wait for them to hatch out into live flies.
By carrying out this process a couple of times a week you can easily keep your mantis fit and healthy with minimum effort required on your part.