Observation of the Week, 8/18/80

This amazing conglomeration of Papilio anchisiades idaeus caterpillars, seen in Mexico by luisguillermog, is our Observation of the Day!

A biologist and amateur wildlife photographer who lives in Cancún, on Mexico’s Yucatan peninsula, Luis Guillermo has been working in the jungle for over decades but has never seen an aggregation of caterpillars like the one above, which he photographed.

“The picture was taken in Dzitnup, a tourist site near to Valladolid, Yucatán, during a [family] trip, [this] July,” recalls Luis. “[This was] outside the “cenotes” X’kekén and Samulá…

I was looking for birds when I saw a stain on a tree, but [what] caught my attention [was] the geometric form and then a slight movement. When I saw through the lens could hardly believe that it was a group of caterpillars. I had to look twice. I had never seen this before and I have worked in jungles for 25 years.

Luis said locals “indicated that they had seen before this type of grouping, but they [did] not give me the common name of the "worms" or were they able to tell me that they were butterfly caterpillars. I knew it after, through iNaturalist Page.”

What Luis saw were the caterpillars of the Ruby-spotted swallowtail butterfly. Females of this species lay eggs close together on the leaves of trees in the Rutaceae, or Citrus family, and according Young, et al (1986), “a major feature of larval behavior in P. anchisiades in both field and laboratory is the close physical contact among individuals.” For the first three instars, the caterpillars hang out on leaves during the day and eat at night. They then relocate to the trunks of the tree for instars four and five.

We suggest that aggregative behavior in the larval stages of P. anchisiades enhances visual crypsis to some predators such as birds and lizards. The combined aggregate of several fifth instars on the bark of the host tree creates the image of a mottled blotch of false lichens and bark on the trunk. Similarly, the tightly packed clusters of younger larvae on the ventral surfaces of Citrus leaves resemble dead or dying plant tissue destroyed by a pathogenic microorganism. (Young, et al; 1986)

Like other swallowtail caterpillars, these evert osmeteria when threatened, and “A strong, disagreeable odor, best described as ‘sweaty socks,’ was apparent when the osmeteria of the last two instars were everted.”

Luis, who has over 1,300 observations on iNaturalist, says he uses the iNat “as a form to show the diversity of the Yucatan Peninsula, because I believe that you can only protect or conserve what is known and with the hope to inspire another to observe the richness of life forms around us.”

- by Tony Iwane


- Check out these videos of Ruby-spotted swallowtail caterpillars molting and then metamorphosing!

- Check out the nearly 500 faved observations from the Yucatan Peninsula!

Posted by tiwane tiwane, August 19, 2017 01:04 AM

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