This fifth instar caterpillar is relatively easy to identify due to the tentacles that extend well beyond the head, almost 3X, the white spots above each of the abdominal legs and well-defined striped pattern.
Fifth Instar - Measured Mid-stage
Fifth Instar Feeding on a Butterfly Weed Flower
Fifth Instar Head Capsule
Fifth Instar Feeding Pattern
Fifth instar caterpillars tend to eat the edges of the leaf, rather than the center. This pattern is a good way to identify if you have a first or second instar or a fourth or fifth present on a milkweed leaf.
Fifth Instar Caterpillar "Flagging"
This fifth instar caterpillar is doing what is called flagging. They eat the petiole of the milkweed leaf (where the leaf meets the stem) which stops the flow of milkweed sap, or latex, to the leaf.
Fifth Instar Recently Molted
Notice the pale head and legs. These will eventually fill with fluid. See the next image.
Newly Molted Fifth Instar Caterpillar
This fifth instar caterpillar has molted and filled with fluid. More often than not, once this is complete, they turn around and eat their shedded skin.
Fifth Instar Eating Skin
Once a caterpillar has shedded their skin, or molted, they fill with fluid for about an hour, then eat their skin.
Fifth Instar with Long Tentacles
The tentacles on a fifth instar are quite long, almost 3 times the length of the head. They often move them around more than other instars.
Fifth Instar in "J" Form Prior to Forming Chrysalis
It can be a little tricky to find fifth instar caterpillars in their "J" form in the wild, but if you look hard enough in an area of milkweed that has obviously had monarch caterpillars feeding on it, you may find one! This one was about ten feet from the nearest milkweed plant, but caterpillars can travel much farther to find a suitable spot to make a chrysalis. They rarely make them on milkweed plants.
Fifth Instar Forming Chrysalis
This is a video of a fifth instar monarch caterpillar forming a chrysalis.