Caterpillar in Borneo Uses Tree Resin to Construct Cocoon
A research team led by Professor William Symondson from Cardiff University has discovered a new caterpillar in Borneo that makes its cocoon out of flakes of dried resin — a sticky substance exuded from trees that hardens over time. The cocoon appears to be unique because no other butterfly or moth is known to make a cocoon from such material.
This particular cocoon consists of two separate walls, built using resin flake, which the caterpillar weaves together using silk. The resin is manipulated by the caterpillar to ensure that the inside is smooth, whereas the external surface is defended by sharp spikes, forged from the rough edges of resin flakes. This physical barrier makes the caterpillar — and later the pupa — hard to reach. The resin also contains a broad range of toxins, ensuring that the caterpillar is well protected from predators.
The caterpillar and its cocoon, which are described in the Journal of Natural History, were found by chance.
“Every year I go out to our field station, Danau Girang, on the Kinabatangan river” he said. “My speciality is entomology and I take groups of students into the forest to look at the amazing invertebrates, from gaudy butterflies to scorpions. One day I spotted this strange red caterpillar behaving oddly on a patch of resin on the trunk of a tree, pointing it out to the students. The caterpillar was mainly bright red, which caught my attention, and hairy. I came back at intervals during the day and photographed the various stages of construction of the cocoon. I had never heard of any caterpillar constructing its cocoon out of resin, but thought at the time that it must be a well-known behavior. When I got back to the UK, I first searched the literature but could find nothing. I then contacted several people at the Natural History Museum in London, including the author, Jeremy Holloway, of the multi-volume books on the moths of Borneo, but none had seen or heard of such behavior before. We know of no other cases from anywhere in the world of a caterpillar making a cocoon out of flakes of resin.”
The discovery has raised questions about how the caterpillar came to utilize such an original strategy.
“It is a wonderful piece of evolution, because the resin is highly toxic and it makes you wonder how this species of caterpillar first started to use such a dangerous material” said Professor Symondson. “Relatives of this moth make cocoons out of pieces of bark, and therefore it is likely that individuals that first built [them] included a proportion of resin into their cocoons, as well as the bark, [and] survived better. The resin not only physically hides the pupa well, but also any inquisitive predator, bird, or insect has to get past a highly toxic barrier. Few are likely to be able to do so.”
The caterpillar species has yet to be identified, but the researchers believe it may be in the genus Negritothripa, in the family Nolidae.
“We still do not know the species,” Professor Symondson said. “Searches in the same area have failed to find another example of this lepidopteran. If we could find a cocoon with the pupa still inside it, we could hatch it out and the mystery would be solved.”
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