Pipevine Swallowtail Caterpillars (Battus philenor) show a similar path toward long horns as Monarch Caterpillars. Pipevine Swallowtail Caterpillar Pipevine Swallowtail Caterpillar Monarch caterpillars grow on milkweed and they have a long pair of horns at both ends of the body.īlack bands are also specific to its body and are mixed with yellow and white bands. However, black spots are visible in the areas that later become long black horns. The first instar of this species is hornless. However, they grow from the second fifth instar, when they are the longest. The horns of the species aren’t visible in its first instar. Monarch Caterpillars (Danaus plexippus) are among the most common caterpillars in North America. Some of the most common North American caterpillars with horns include the following species. Other types of caterpillars fully covered by horns (such as the Zebra Longwing Caterpillar) use a possibly-threatening look to keep larger predators such as birds away.Ī higher density of horns also keeps smaller predators such as wasps away. Some of these caterpillars absorb toxins from their hosts which makes them unpalatable for their predators which may perceive them as venomous and stay away. Multicolored red and yellow horns are further distinguishable on the species. Some may be brown while others may be green. Most horns on caterpillars are black or colorful. Venomous horns with spikes are also not actively used by the species as they represent passive defensive mechanisms that only hurt predators in case of direct contact. In reality, this horn has no type of function apart from being a visual deterrent. It may be perceived as a stinger, by different types of predators. One horn is typically seen at the rear of the body. Keeping predators away with a horn is often subject to having one horn only. Living in groups is another strategy some species rely on to keep predators away. While not truly dangerous to humans, some caterpillar horns may lead to skin-level reactions such as rashes or even dermatitis.Ĭaterpillars may rely on horns as a single line of defense or as one of the multiple strategies to avoid predation. They are often differently colored from the rest of the body so they stand out immediately. Horns can be bright, dark, or even black. Many fear these horns due to their color or their shape. Mostly ornamental, horns are an evolutionary trait that aims to scare off predators. Theories behind the horns of caterpillars are based on the self-defense principles which are evolutionary traits to keep predators away.

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