Monarch Butterfly Development

Daily photos of every stage of development from egg to adult, including caterpillar and chrysalis. There is also a chart with a quantitative analysis of caterpillar growth. Please see the About page for more information and commentary.
Day 1: July 23, 2020 4:23 PM  This photo was taken about 5.5 hours after a female monarch butterfly visited milkweed plants in my yard and presumably laid this egg, which was the only one I found.  The egg had a length of about 1.4 mm and a maximum width of about 1 mm as determined by image analysis. Day 2: July 24, 2020 9:35 AM  There is no obvious change from the previous day. Day 3: July 25, 2020 8:56 AM  There is no obvious change from the previous day.
Day 4: July 26, 2020 9:56 AM  The egg is starting to hatch. Day 4: July 26, 2020 4:04 PM  About 6 hours after hatching began, a tiny caterpillar has emerged.  There is no sign of the egg shell, which was probably eaten by the caterpillar.  At this point, it does not have the colored bands typical of monarch butterfly caterpillars.  The length and width were estimated by image analysis.  The volume was estimated from the length and width, assuming a cylindrical shape.  Length=2.41 mm.  Width=0.58 mm.  Volume=0.63 cubic mm. Day 5: July 27, 2020 9:30 AM  The caterpillar has already grown considerably and is starting to show the colored bands typical of monarch butterfly caterpillars.  Length=3.57 mm.  Width=0.76 mm.  Volume=1.612 cubic mm.
Day 6: July 28, 2020 10:00 AM  Length=5.56 mm.  Width=1.18 mm.  Volume=6.06 cubic mm. Day 7: July 29, 2020 9:27 AM  Length=6.60 mm.  Width=1.29 mm.  Volume=8.61 cubic mm. Day 8: July 30, 2020 8:43 AM  Length=9.01 mm.  Width=2.17 mm.  Volume=33.3 cubic mm.
Day 9: July 31, 2020 8:24 AM  Length=8.29 mm.  Width=1.82 mm.  Volume=21.5 cubic mm. Day 10: August 1, 2020 8:34 AM  Length=14.20  mm.  Width=2.71 mm.  Volume=82.2 cubic mm. Day 11: August 2, 2020 9:26 AM  Length=16.6 mm.  Width=2.82 mm.  Volume=104 cubic mm.
Day 12: August 3, 2020 9:10 AM  Length=26.2 mm.  Width=4.49.  Volume=415 cubic mm. Day 13: August 4, 2020 9:04 AM  Length=20.8 mm.  Width=4.79 mm.  Volume=374 cubic mm. Day 14: August 5, 2020 8:45 AM  Length=28.6 mm.  Width=5.21 mm.  Volume=608 cubic mm.
Day 15: August 6, 2020 9:00 AM  Length=39.7 mm.  Width=6.77 mm.  Volume=1429 cubic mm. Day 16: August 7, 2020 9:19 AM  Length=48.1 mm.  Width=8.81 mm.  Volume=2932 cubic mm. Day 17: August 8, 2020 8:45 AM  The caterpillar has stopped feeding, climbed to the top of the cage, and attached itself.  It is now a prepupa.
Day 17: August 8, 2020 2:02 PM  Pupation has occurred!  A wing anlage is visible at the right side of the chrysalis, although it was not visible in the caterpillar or prepupa.  It must have been hidden by the skin. Day 18: August 9, 2020 6:41 AM  The chrysalis looks about the same as when pupation occurred. Day 19: August 10, 2020 9:41 AM  The chrysalis is somewhat darker and more opaque
Day 20: August 11, 2020 9:20 AM  There's not much change from the previous day. Day 21: August 12, 2020 9:05 AM  There's not much change from the previous day. Day 22: August 13, 2020 8:22 AM  There's not much change from the previous day.
Day 23: August 14, 2020 10:30 AM  There's not much change from the previous day. Day 24: August 15, 2020 9:16 AM  There's not much change from the preious day. Day 25: August 16, 2020 9:38 AM  There's not much change from the preious day.
Day 26: August 16, 2020 9:38 AM  The chrysalis has blackened, but become more transparent.  The aduit wing color and wing veins are visible through the cover. Day 26: August 16, 2020 1:41 PM  Eclosion has occurred, and the wings have unfolded.  The remains of the chrysalis can be seen at the top left.  Due to rainy weather, the adult butterfly was kept in its cage another night with food in the form of a very ripe plum that was cut open, and released the following day. Caterpillar Growth Analysis  A plot of log(Volume) vs. Hours of Growth gives a straight line with a high correlation coefficient (R), indicative of exponential growth.  The straight line shows the  fitted exponential equation.  The caterpillar almost doubled in volume every day.  The calculated doubling time was 24.8 hours.  On the basis of the fitted equation, the volume (and mass, which is proportional to volume), increased at least 2,500 times from hatching to the maximum size on Day 16.  There are undoubtedly measuring errors, especially for the earliest stages.  Also, it seems likely that growth paused temporarily during molting.  The assumption of a cylindrical shape is an approximation.  Nevertheless, the results strongly indicate an extremely fast exponential growth. : exponential growth