Having only been with us for a week, our caterpillars have fattened up quickly! It is natural for them to put on a lot of weight, up to 2700 times their original weight, from the nutrition of the Milkweed leaves alone. What you may not know is that the Milkweed sap makes them poisonous to other animals. To warn predators of their bad taste, nature has equipped them with the black and white striped pattern, a system known as aposematism. Aposematic signals can include coloration, smell, and sounds. This is beneficial to both predators and prey because the predators avoid potential harm, and prey avoid being eaten!
Why are the Monarch caterpillars poisonous? The Milkweed plant contains a chemical called Cardenolides. This chemical when ingested by the caterpillar in large amounts makes them poisonous to many vertebrates, even as an adult butterfly! It has even been observed that Monarch caterpillars who have ingested Milkweed with higher amounts of Cardenolides, they are less likely to be predated on by animals like birds and mice.
Take a look at this shot of our growing critters. Hard to believe such harmless looking creatures can be so unfavorable to other animals!