I have just observed that some 1st instar larvae move outside of the petridish / not live on food plant during studying the life cycle of butterflies in laboratory conditions. What is the reason behind this? Maybe they did not find a suitable environment inside of the petri dish? Just a guess.
Why are some of the first instar larvae of butterflies alive outside of the food plant?
It is very commonly noticed that first instar caterpillars of many moths, just after hatching, ‘wander’, may be in search of younger or tender portions of leaves, or sometimes they end up at the tips of leaves where the hardness is less.
I agree with the above answers and add that certain “wandering” of the 1st instar caterpillars is a perfectly natural phenomenon. In nature, females sometimes do not lay their eggs directly on food and thus, freshly hatched larvae must first look for their food.
There are many reasons for such behaviour. In containment as someone written crowd and microenvironment matters much. Some should be reared in isolated tubes/vials due to cannibalism. Check these point with your species of study.
Unless this is a ‘social’ species, many/most caterpillar species will not feed if crowded. And don’t forget: even artificial diet changes over time as it dries out -as do cut leaves – and some plant material may respond to feeding. Those factors can lower food quality and stimulate movement away.