“Growing up Monarch” is an on-going segment in the River Bend blog that follows the lives of several monarch butterflies as they grow from egg, to caterpillar, to chrysalis, to adult. We’ll be updating with photos and fun facts and observations throughout the summer!
It’s been a week since we last looked at the monarchs that River Bend is raising, and a lot has happened in those seven days! In the life of a caterpillar, change happens quickly, and with just about a month to go from a tiny egg to a full-fledged butterfly, there’s no time to waste in putting on those growth spurts, and our resident royalty has been doing just that.
The smallest of the three caterpillars remains a “1st instar”, though its larger cage mates have already molted. Photo credit: Stephanie Rathsack
Ever since day one, these larvae have been professional eating machines—spending most of their day chowing down on the provided milkweed leaves. You’ll recall from our last post that monarch larva feed exclusively on milkweed—refusing any other offered vegetation. They do, however, start their lives off with a slightly different meal: their own eggshell. And unfortunately, in some cases, the eggshells of other caterpillars. Such was the case for our River Bend monarchs.
Skin clings to the back of a newly molted 2nd instar caterpillar.
Photo credit: Stephanie Rathsack
Last week we had a total of three caterpillars and one ready-to-hatch egg, but since then we’ve dropped by one, as one of the caterpillars made a meal out of the last egg before it could hatch. This cannibalistic behavior may be another reason for why female monarchs lay only one egg per plant, as the larvae appear to have no qualms about siblicide. With that being said, we now have a grand total of three healthy caterpillars, and all danger of competition between them has passed. Since then, they have continued to feed voraciously. They no longer eat in the characteristic circle pattern of newly hatched caterpillars, instead they now chew all the way through the leaves, creating small holes as they do so.
While nearly the same size, the caterpillar on the left is a recently molted 2nd instar, while the caterpillar on the right is still a 1st instar, preparing to molt—indicated by the dropped head capsule and the white silk holding it in place. Photo credit: Stephanie Rathsack
With all that eating, it’s no surprise that they’ve already increased in size. As of Tuesday May 30th, one caterpillar had already molted into its 2nd instar stage, with another preparing to do so as well.
Rearing its head may help this 3rd instar navigate its surroundings. Photo credit: Stephanie Rathsack
The third caterpillar is slightly smaller, and took longer to be ready to molt its skin. This molting, or “ecdysis” as it’s referred to by scientists, will occur several times during the caterpillar stage and can be predicted by several behaviors as well as physical changes—the most obvious being a lack of appetite. Our caterpillars would stop eating and stop moving completely as they prepared to shed their skin. Prior to molting, the caterpillars will lay down a layer of silk that helps hold them in place.
Upon completing its molt, the caterpillar’s new skin is soft and light colored—obvious in this photo as seen by its yellow head and legs. These parts will darken over the next few hours, but until then the larva is at its most vulnerable, similar to a crab without its shell. Photo credit: Stephanie Rathsack
By Saturday, June 3rd, all three caterpillars had shed twice, and were officially “3rd instars”—the largest even preparing to molt again to become a 4th instar.
The smallest of the three caterpillars was once again the last to prepare to molt, though on Saturday it was in search of a location to do so as it roamed its habitat, occasionally rearing its head up—which may assist sensing its environment, as well as start loosening the older skin and head capsule.
Two third instar caterpillars, with the individual in the foreground preparing to molt. Note the dropped head capsule, with the newer, lighter colored skin above it. Photo credit: Stephanie Rathsack
It takes caterpillars roughly two weeks to go from 1st instar to chrysalis, and our three caterpillars, having hatched on Friday, May 26th should be preparing to pupate late this upcoming weekend. They still have some growing to do however, and will continue feeding every day in order to do so.
This 3rd instar expelled some of its waste during observation. Caterpillar poop is known as “frass” in the scientific world, and this caterpillar displayed an odd behavior as it promptly turned around, and picked the frass up, moving it around several times before leaving it behind.
Photo credit: Stephanie Rathsack
Today, Monday the 5th, all three caterpillars have shed their skin and are officially 4th instars. They have bold stripes along their bodies, large banded heads, and front antennae that droop down past their head capsules—all key characteristics of 4th instar caterpillars. Within the next few days they’ll shed again to become 5th instars, and then finally, they will shed their skin a final time in order to transform into a chrysalis.
A view of all three caterpillars as viewed on Monday, June 5th. All three are considered “4th instars” at this stage, despite the differences in size. Photo credit: Stephanie Rathsack
Want to learn more?
Stop by our interpretive center this weekend to talk to a naturalist and see the monarchs for yourself! The monarchs will be viewable as follows:
Interested in getting more involved?
River Bend will be offering MLMP trainings to teach interested members of the community to become certified MLMP volunteers! Monitor at home or at River Bend, and help save this amazing insect from extinction.
Register online to attend the training scheduled for June 10th from 1:00-4:00pm.
For more information, see our website at: http://www.rbnc.org/