I have had the monarchs for a little over a week and to say the change in them has been huge would be an understatement! (to read about what got me into this project and why monarchs are important click here: https://doctorb.blog/2019/08/06/raising-monarchs-part-1/). Every morning, after my cup of coffee is ready, I go out on the back porch to take a peek and see what they have been up to. To watch how quickly they grow is utterly amazing.
Let’s talk about the first two stages of their four stage life cycle, as these are the stages we have been fortunate to observe in our little set up so far. Life for a monarch begins as an egg. The female monarch, the mom, will lay an egg on the underside of a milkweed leaf, typically laying only one egg per plant (which is a good plan given how much these VERY hungry caterpillars can eat!). The egg is small, about 1 mm in size and creamy white to yellow in color with longitudinal ridges from base to tip and a wax coating on the shell to prevent desiccation. Each mom will typically lay 300-500 eggs over a 2 to 5 week period. As the caterpillar develops inside the egg you can see it’s dark coloured head near the top. After about 4 days, with the actual length of time being temperature dependent and ranging from 3-5 days, the caterpillar will hatch out.
The first meal for a caterpillar, or larva, is to eat the egg case that it just emerged from. After that it is an all-you-can-eat buffet of milkweed leaves. And boy do these guys eat! In fact they spend the majority of their time chomping away, with little time to rest. My six year old even claims he can hear them eating when he sits close to the enclosure watching them. But there is a good reason for all this chowing down – they grow at an incredible pace. In fact, according to Mission Monarch of the Montreal Insectarium, their weight will increase 2,700 times in just two short weeks! In order for their bodies to accommodate all this rapid growth, given the outside of their body is not stretchy skin like ours but a hard exoskeleton, they most molt (shed their skin). I have not found any shed skin and I did wonder about this but apparently it is often eaten by the caterpillar before it goes back to its normal meal of milkweed. The interval between each molt is called an instar in the insect world and monarch caterpillars have 5 instars, starting out as a first instar larva upon hatching and finishing as a fifth instar larva prior to entering the pupal stage.
Like all other insects, monarch larva have 3 body segments – a head, thorax and abdomen. The head has short antennae, their mouth and 12 simple eyes (ocelli) that can detect changes in light level. Surprisingly with all those eyes, the caterpillars vision is quite poor. The thorax segments each have a pair of jointed legs, while some the abdominal segments have false legs (prolegs) that look like little suction cups with hooks that help them attach onto surfaces. They also have a spinneret on their head that produce silk threads to further tether them in place. The caterpillars also have two sets of black fleshy tentacles, a pair of long ones at the front and a shorter pair at the back – that look like antennae but are not, though they do provide some sensory information. But the most striking feature, and what they are most recognized for is the bright yellow, black and white stripe pattern to their body.
I am very pleased with how the caterpillars are growing! I need to give them fresh leaves every day, with them eating about one medium sized leaf per caterpillar per day. On Thursday as the kids and I sat watching them on the back porch I noted our oldest caterpillar, a fifth instar, was not chomping away at the fresh leaves but instead was busy exploring the enclosure. He (or she) walked along the glass a bit but spent most of his time going up and down one of the sticks that I had placed inside. On Friday morning when I went to check I discovered why – he had been looking for a suitable spot to pupate. And there he was on Friday, with a silk pad anchoring him upside down to the stick he had been so intent on exploring. He was in what is referred to as the “J-hang”, getting ready to enter the next stage of his life cycle. What did the process of transformation look like and what happens in the final two stages? You will have to wait for part 3 and part 4 to find out!
Doctor B 