Similar to the pine processionary caterpillar, the bag shelter caterpillars live in a group in a silk bag, coming out at night to feed and following one another head to tail in single-file fashion. However, their health risk is far greater than that of the pine processionary caterpillar. In fact, these guys are considered a health hazard in South America. The venom that comes from their bristles is a potent anti-coagulant, meaning anything that is unfortunate to brush up against them is at risk of bleeding profusely (even to death) from the smallest cut, or from internal bleeding.
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