Mexican Fritillary (Euptoieta hegesia) life history
Mexican Fritillary (Euptoieta hegesia) Life History

Egg; shows development, 11-29-11

Day-old caterpillar, 12-2-11

Caterpillar is turning orange, 12-4-11

Second instar, 12-9-11

Just entering third instar, 12-12-11

Fourth instar, 12-18-11

Mexican Fritillary (see text comments)

Variegated Fritillary

Mature caterpillar is about 4 cm in the fifth (final) instar, 12-26-11

Preparing to pupate, 12-27-11

Chrysalis, 12-28-11

Ready to emerge, 1-17-12

Fresh adult Mexican Fritillary, ventral, 1-18-12

Fresh adult Mexican Fritillary, dorsal, 1-18-12

Riverside in Salineņo, TX, is the best place I know of in Starr County to find Mexican Fritillaries. Cotton-leaf passionflower, Passiflora foetida, grows there in abundance, and it is the only potential host plant I have identified in that area. I've often watched the fritillaries fly around those passion vines, but I've yet to see a female depositing eggs.

In late November, 2011, I captured a female that clearly was carrying eggs. I placed her in a container with several pieces of the cotton-leaf passionflower, and waited expectantly. However, after three or four days she had not laid any eggs. Early on a Sunday afternoon, I also offered her Damiana (Turnera diffusa), a native host that I have in the yard. That evening I decided to release the butterfly. For some reason, I did not inspect the cuttings until Tuesday. When I did, I was pleased to discover that the female had left close to twenty eggs on the Damiana before she was released.

The caterpillars emerged on 12/2, five days after the eggs were deposited. I decided to separate a single caterpillar to be the subject of this essay. I placed this one on a stem of Cuban Buttercup (Turnera ulmifolia), an ornamental relative of Damiana. This caterpillar grew much more quickly than the rest, pupating more than a week before any of the other caterpillars did.

Meanwhile, I had 18 more caterpillars and I was very curious: why did the female refuse to lay eggs on Passiflora foetida? Did she reject it because the species is always unsuitable as a host plant, or because these particular vines were unacceptable? (They were certainly not in good shape.) What other plants would Mexican Fritillary caterpillars eat? When the caterpillars had gained enough size for me to experiment, I offered a variety of passion vines that I had available. Natives P. tenuiloba and P. suberosa were rejected, as was an unidentified ornamental vine. But P. foetida was accepted. It is possible, therefore, that the fritillaries do use foetida when it is in good condition (or "in season").

Face of Mexican Fritillary

While I was investigating the host-plant issue, another question arose: why was the isolated caterpillar growing so much more quickly than the others? For 2-3 days it had been kept under slightly warmer temperatures, but that slight advantage didn't seem to explain the faster growth. On December 29 the study caterpillar had pupated, but the rest were nowhere near that stage. I wondered if food might have played a roll in development. I divided the remaining 18 caterpillars into three groups. One group was fed Damiana, one Cotton-leaf Passionflower, and one, Cuban Buttercup. The Cuban Buttercup group did seem to show slightly accelerated development, but results were inconclusive. It would be interesting to repeat this experiment with first-instar caterpillars.

When the Mexican Fritillary caterpillar is ready to pupate, it often makes a very loose tent by tying a few threads of silk to leaves or stems near where it will attach itself. The amazing beauty of the chrysalis is difficult to capture in a photograph. Where the camera records white patches, the eye beholds metallic reflections that make the chrysalis appear to be made of gold or silver.

Caterpillars of the Mexican Fritillary and the Variegated Fritillary are very similar, and both may be found on the same host plants. The Mexican Fritillary larva can be identified by its more-or-less continuous black and white dorsal stripe. Also, the bases of the spines on each side of this stripe are surrounded by red. By contrast, the Variegated Fritillary has a red/orange dorsal stripe, possibly with some white spotting. The spine bases interrupt the subdorsal white stripe. These keys are identified in the pictures to the right that follow the fourth-instar.

In 2008, I was able to photograph an adult just after it emerged from the chrysalis. Those pictures may be seen here.

Mexican Fritillary Page