On Monday, he ate through one apple. On Tuesday he ate through two pears. On Wednesday he ate through three of his friends. Wait that’s not right….. What just happened?
A recent study published in Nature Ecology and Evolution journal found that chemicals released by plants can cause caterpillars that eat them to resort to means of cannibalism. Researchers behind the study looked at tomato plants and discovered that they were producing a chemical called methyl jasmonate when stressed or damaged. When caterpillars nibble on the leaves of these plants, the plants get stressed and release this chemical which then the caterpillars take in when they eat the plant. Nearby plants can also sense this and also begin to produce methyl jasmonate building a chemical camouflage around themselves and protecting the plants from being eaten. Now that all the plants taste terrible, the caterpillar has no food and turns to the next available meal which happens to be each other.
Interestingly enough, cannibalism is not as rare in bug and insect populations. Some species of bug larvae actually eat the unhatched eggs of their siblings. Other bug behaviors can also be explained by cannibalism as well. For example, in 2008, a study found that locusts flocked together because they were afraid that the locusts flying behind them will try to eat them. Another study in 2010 was more specific to caterpillars and showed that caterpillars may resort to cannibalism if the food available to them isn’t plentiful or good enough.
Now lets think about this from a disease ecology perspective and say that these caterpillars carry viruses that harm their species. Cannibalism is an easy way to transmit the disease to one another and so when one caterpillar bites another, it is spreading the disease throughout the population. This greatly benefits the plants because not only are they protected by pests but since the disease is rapidly spreading among these caterpillar predators, the herbivore population is gradually decreasing as well. Cannibalism among herbivores may also be beneficial. By eating each other, caterpillars are virtually removing most of the competition from the food chain and are sustaining the population for a time when food is scarce.