The announcement of our Monarchs in Space project in November generated many questions, the most common of which was: "Why send monarchs into space?" Here are the two main reasons we participated in this program:

1) Monarchs are an iconic species and it seemed reasonable to suppose that by following the growth and development of monarchs in space, children and the public would gain a sense of the challenges of life in space and be able to connect with space science and the space program.

2) Monarchs seem to be a gravity dependent species. As larvae they exhibit negative geotaxis (always go up), seek horizontal surfaces upon which to pupate, and expand their wings in a manner that suggests gravity has a role. The question was: how will such a gravity dependent species function in space where vertical and horizontal do not exist? Will they be able move through the life stages as they do in gravity, or will they encounter difficulties - and if they do, will they be able to compensate for the near absence of gravity?

The following text summarizes what we have learned from our observations of both the Experimental Habitat aboard the International Space Station and the Control Habitat maintained in the laboratory of BioServe Space Technologies at the University of Colorado in Boulder. What the students learned from participating in this program will be the subject of another text.


Early on Sunday morning the 15th of November 2009, each habitat was stocked with a special artificial diet and three early fourth instar monarch larvae provided by Monarch Watch. The habitats were placed in a special chamber and transferred to NASA personnel who delivered the chamber to the space shuttle Atlantis later that day.

At 2:28pm EST on the 16th of November, Atlantis lifted off from Launchpad 39A at the Kennedy Space Center in Florida. Atlantis docked with the International Space Station (ISS) on the 18th and the chamber with the monarch habitat was transferred from Atlantis' mid-deck to an experiment rack in the Kibo Laboratory on the ISS.

Over the next 25+ days the three caterpillars fed, molted, pupated, emerged, and expired in both the Experimental and Control Habitats, but they did so differently in the two habitats. In brief, the caterpillars in the Control Habitat performed all life functions as expected. The monarchs in the Experimental Habitat in space were affected by microgravity at every stage; however, they surprised us with their adaptability.

At the outset, we envisioned at least five challenges for the Monarchs in Space: clinging to the substrate, molting to the chrysalis/pupa stage, affixing the cremaster to the silk pad, emerging from the pupal cuticle, and expanding the wings.


So how did the monarchs perform each of these functions in the Experimental and Control habitats?

Clinging to the substrate, feeding and location.

Experimental Habitat: The caterpillars seemingly had no difficulty clinging to the substrate and at no time did any become dislodged and float. The caterpillars fed where they found food and did not feed preferentially at the “top” of the container. These caterpillars spun more silk than did the caterpillars in the control.

Control Habitat: The caterpillars fed mostly toward the top of the food unit but showed more variability in where they fed than seen in our lab.

Hanging up, forming Js.

Experimental Habitat: Perhaps due to the lack of a reference to vertical or horizontal, each caterpillar chose a different surface upon which to spin a silk bed and silk pad for pupation. One chose the plexiglass at the left front of the chamber, another the upper right back corner of the chamber, and the third chose the lower right corner. Each attached their anal prolegs to the silk pad but when they dropped into what would have been a J under normal conditions, they curled into tight Cs with the head of the caterpillar brought close to the abdomen. At no time did they stretch out into the normal J shape.

Control Habitat: All three larvae chose to hang up and form Js beneath the top of the container – the only available horizontal surface.

Shedding skin, attaching the cremaster to the silk pad.

Experimental Habitat: Although all three caterpillars were able to shed their skin, in two cases the skin formed a cap at the end of the abdomen and the cremaster was not withdrawn from this skin and inserted into the silk pad. The third caterpillar did shed its skin but failed to attach to the silk pad and became the first floating pupa.

Control Habitat: All three larvae shed the skin completely and attached the cremaster to the silk pad in a normal fashion.

Emerging, expanding the wings

Experimental Habitat: Because of the failure to attach the cremasters to the silk pad, all three butterflies had to emerge from pupae that had become dislodged and were therefore floating. Although floating, the movements of the emerging butterflies caused them to come into contact with the sides of the habitat and these exertions allowed them to free themselves from the pupal cuticles. How they accomplished this feat is not apparent in the videos we have seen to date.

Without the aid of normal gravitational forces, the emerging butterflies had to force the wings to assume a flat aspect. Pumping fluid into the wings did not seem to be sufficient in itself for the monarchs to extend their wings directly over their backs. The process took at least 15 minutes and the new adults kept moving most of this period, often from side to side - a kind of a rocking motion. During most of this time, the wings folded back on themselves. Surprisingly, two of the butterflies were able to expand the wings sufficiently so that, if on earth, they would have been able to fly. The wings of the third and last butterfly to emerge, did not form normally. This deformity might have been due to the imperfect form of the chrysalis as much as to the conditions in space.

Control Habitat: All three emerged from the pupae and expanded their wings in a normal fashion. No deformities were evident.


Earthbound monarchs seem to respond to gravity and perhaps even utilize gravity while progressing from the caterpillar to the adult stage. The results indicate that pupation and emergence were strongly affected in the near weightless conditions aboard the ISS. The inability of all three caterpillars in the Experimental Habitat to properly attach the cremasters to the silk pads during pupation was striking. Similarly, the nearly constant movement of the butterflies expanding their wings, and the amount of time taken to go through this process, suggests that, on earth, gravity does play a role in the expansion of the wings.

The overall results of both the Experimental and Control groups, as well as the well-known patterns of monarch behavior on earth, indicate that monarchs have a sense of gravity. This conclusion raises the most interesting question of all: How do monarchs caterpillars and adults sense gravity and where is the gravity sensor (or sensors) located? Further, is it possible that gravity sensors in adults are different from those in larvae?

Vertebrates have balancing organs, usually in the inner ear, that work together with vision to maintain proper orientations with respect to gravity. Plants have well known tropisms and show both negative and positive responses to gravity under different conditions. The genetic basis for some of these plant responses is also known but relatively little is known about how invertebrates sense gravity.

This study shows that although monarchs are well studied and much of their biology is known, there is still much to learn.

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