Silkmoth Caterpillars from Mexico: Arsenura armida

Subject: Caterpillars in the Yacatan jungle
Location: Coba ruins , tulum area
November 21, 2016 12:29 pm
Please take a look at this Catapillar. We found clusters of these in the jungle at the coba ruins in the tulum area. At the base of the tree , directly below them was a whole bunch of little pellets. We’re curious what this Catapillar is and what it turns into. I hope you can help.
Signature: Petra

Arsenura armida aggregation
Arsenura armida aggregation

Dear Petra,
This Project Noah image gives us confidence that this is an aggregation of Caterpillars of the Giant Silkmoth
Arsenura armidaWe have several images in our archives that look similar.  Thanks so much for including the image of the droppings.  This Cortland Faculty website has some nice information including:  “This large Neotropical silkmoth is the only species in the genus Arsenura that exhibits sociality.  Other Arsenura are solitary and cryptic, but A. armida has adopted an aposematic and gregarious lifeyle.  It may be the only social representative of the subfamily Arsenurinae which occurs from tropical Mexico to northern Argentina and contains approximately 57 spp., very few of which are known from the early stages (Lemaire, 1980; Hogue, 1993).
Arsenura armida occurs from tropical Mexico to Bolivia and southeastern Brazil.  In the tropical dry forest of Pacific Mexico and Central America, its caterpillars are found on Guazuma ulmifolia (Sterculiaceae), Rollinia membranacea (Annonaceae), and Bombacopsis quinatum (Bombacaceae) (Janzen and Hallwachs, 2002).  Larvae emerge shortly after the rainy season in May, after passing the long dry season as a solitary and dormant pupa in a chamber excavated 2-10 cm below the soil surface.  Part of the first generation enters a dormant pupal stage and part ecloses about 35-55 days after pupation, to create a second generation in November-December.  All of the second generation pupae become dormant until the following start of the rainy season.
The young larvae are brightly aposematically ringed yellow and black with red heads, and remain together diurnally feeding side by side in large masses on the leaves.  Costa, Fitzgerald, and Janzen (2001) studied this species in Santa Rosa National Park, Costa Rica, and showed that the larvae use a trail pheromone to maintain group cohesion. Larval trail-following can be elicited by surface cuticular material collected by wiping from the venter and dorsum of the abdomen of A. armida caterpillars, as well as crude extracts of homogenated somatic tissue.  The long-lived trail marker appears to be a component of the cuticle passively deposited from the posterio-ventral region of the abdomen as larvae travel over the host plant.
In the fourth instar,
A. armida larvae dramatically change their foraging strategy, switching from nomadic to central place foraging.  Costa, Gotzek, and Janzen (in review) documented the details of this behavioral shift: in central place foraging mode the caterpillars begin to rest diurnally in large conspicuous masses on the lower trunk and underside of larger branches, mobilizing at dusk to forage nocturally as solitary larvae in the canopy.  They return to the lower trunk at dawn, using tree architecture and their trail pheromone to relocate conspecifics (which are generally confamilials) upon descending.  Although larvae often reuse the same resting (bivouac) sites, individual caterpillars do not exhibit strict site fidelity and may shift among sites once descended.  This shift in foraging behavior entails a concomitant change in reaction to the information content of their trail pheromone, from maintaining groups as the caterpillars move from patch to patch, to relocating distant resting sites.”  Based on that information, your individuals are fourth or fifth instars, meaning more mature caterpillars.

Droppings from Aggregation of Arsenura armida Caterpillars
Droppings from Aggregation of Arsenura armida Caterpillars

Thank you very much Daniel.
You have been so helpful. What a cool resource you are.


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