Diaethria – a festive caterpillar with antlers!

In my last trip to the Amazon basin of Ecuador I had the fortune of meeting Paul Bertner, an acclaimed photographer and adventurer. I have been following his image posts and trip reports since I cannot remember when (and you should too!), and was excited to spend some time in the field with him, in hopes of learning some new tricks. It was great fun to discover hidden gems in the rainforest together, while discussing arthropod biology, conservation and photography.

During one of our night hikes we came across a tiny green caterpillar that was resting on a silky retreat on top of a leaf. At first glance it did not look very special, but then I noticed that its head featured two enormous antler-like horns. The horns were almost half the caterpillar’s body length! They were not simple straight horns, but rather complex structures that included many branches and hairs. I recognized the caterpillar as a member of tribe Biblidinae in the butterfly family Nymphalidae, but only later learned that it belongs to genus Diaethria.

Eighty-eight caterpillar (Diaethria sp.) with complex antler-like horns. Amazon Basin, Ecuador

Eighty-eight caterpillar (Diaethria sp.) with complex antler-like horns. Amazon Basin, Ecuador

Despite their small size, Diaethria butterflies are quite well-known thanks to the characteristic pattern on the underside of their hindwings. Circular bands in black and white surrounding black dots, giving the impression of the letters BB, Bd or the the numbers 88, 89, 69 etc’. The common names “88 butterfly” and “89 butterfly” are typically used for species in this genus. They are often seen puddling – an interesting behavior in which butterflies take up minerals from mud, sweat and feces.

Eighty-eight caterpillar (Diaethria sp.) is sometimes seen waving its horns while walking.

Eighty-eight caterpillar (Diaethria sp.) is sometimes seen waving its horns while walking.

Upon seeing the caterpillar I knew exactly how I want to photograph it. I wanted a frontal, head-on photo of the caterpillar’s head with the antlers stretched up in their full glory. What photo is more suitable for the holiday season than a festive caterpillar? Unfortunately, I did not have my high magnification MP-E lens with me (as mentioned, the caterpillar was tiny), so I gently collected it to photograph later. Let me tell you, photographing it was not an easy task. It seems that the caterpillar’s default behavior is to rest face down on the leaf, preventing any view of its antlers other than a dorsal one. It literally took hours to get it to change position, and I had to come up with a creative solution to get something remotely similar to the photo I had in mind.

This deer-mimicking caterpillar wishes you happy holidays and a happy new year!

This deer-mimicking caterpillar wishes you happy holidays and a happy new year!

One question that comes to mind is how do these caterpillars molt with such long head protrusions? Do the horns come out already stretched from the old head capsule or are they compressed as horn “buds” that inflate later? And what are those horns good for? They are most likely an adaptation against predators, but it is hard to say exactly how they are used. They can be used as defense to push away ants from attacking the caterpillar, or maybe the caterpillar drives away parasitoid wasps by waving the antlers from side to side. Hopefully someone will be able to document their function in the future and shed light on these remarkable structures.

7 thoughts on “Diaethria – a festive caterpillar with antlers!

  1. Darcy McClelland

    How wonderful that you met Paul! I, too, having been following his photo posts, albeit on flickr. Paul takes some amazing shots … as do you, Gil. Love your little antler cat photos. And may you have a wonderful holiday season!

  2. Gil, did Paul also shot this caterpillar? (It’s my pleasure to identify many of his butterfly larvae and pupae.) If you post a photo of the entire body, I can probably provide an ID. Best wishes!

    • Unfortunately, Paul was too busy taking photos of other interesting insects. He did not get around to photograph this caterpillar.
      I admit that I too do not have a full body shot of the caterpillar, as I was focused on getting just the head shot. But it means that now I have a new goal for my next visit!

  3. Gil, please know that without seeing its entire body, Callicore is also a definite possibility, with both genera having multiple species in Ecuador. FYI, the “antlers” (scoli), which are indeed compressed buds that begin to expand immediately upon release from the previous head capsule, are almost certainly defensive in function. Having reared many such Biblidinae, they typically swing their heads violently when alarmed, agitated, or encountering another caterpillar on the hostplant.

    • Fascinating information, Thanks Keith!
      I know that Callicore is also an option. In all my visits to the site (should be around 10 visits by now) I have recorded only adults of Diaethria, so I assumed that might be the best guess for the caterpillar’s ID. But I completely agree that Callicore is also possible.

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