page_title: Plant defense against herbivory
section_title: Records of herbivores
hierarchical_section_title: Plant defense against herbivory / Evolution of defensive traits / Records of herbivores
caption_attribution_description: Plain tiger caterpillar in first instar. creating a moat on leaf of calotropis gigantia
context_page_description: Plant defense against herbivory or host-plant resistance describes a range of adaptations evolved by plants which improve their survival and reproduction by reducing the impact of herbivores. Plants can sense being touched, and they can use several strategies to defend against damage caused by herbivores. Many plants produce secondary metabolites, known as allelochemicals, that influence the behavior, growth, or survival of herbivores. These chemical defenses can act as repellents or toxins to herbivores, or reduce plant digestibility.
  Other defensive strategies used by plants include escaping or avoiding herbivores in any time and/or any place, for example by growing in a location where plants are not easily found or accessed by herbivores, or by changing seasonal growth patterns. Another approach diverts herbivores toward eating non-essential parts, or enhances the ability of a plant to recover from the damage caused by herbivory. Some plants encourage the presence of natural enemies of herbivores, which in turn protect the plant. Each type of defense can be either constitutive, or induced.
context_section_description: Our understanding of herbivory in geological time comes from three sources: fossilized plants, which may preserve evidence of defense (such as spines), or herbivory-related damage; the observation of plant debris in fossilised animal feces; and the construction of herbivore mouthparts.
  Long thought to be a Mesozoic phenomenon, evidence for herbivory is found almost as soon as fossils which could show it. As previously discussed, the first land plants emerged around 450 million years ago; however, herbivory, and therefore the need for plant defenses, has undoubtedly been around for longer. Herbivory first evolved due to marine organisms within ancient lakes and oceans. Within under 20 million years of the first fossils of sporangia and stems towards the close of the Silurian, around 420 million years ago, there is evidence that they were being consumed. Animals fed on the spores of early Devonian plants, and the Rhynie chert also provides evidence that organisms fed on plants using a "pierce and suck" technique. Many plants of this time are preserved with spine-like enations, which may have performed a defensive role before being co-opted to develop into leaves.
  During the ensuing 75 million years, plants evolved a range of more complex organs – from roots to seeds. There was a gap of 50 to 100 million years between each organ evolving, and it being fed upon. Hole feeding and skeletonization are recorded in the early Permian, with surface fluid feeding evolving by the end of that period.
caption: A plain tiger Danaus chrysippus caterpillar making a moat to block defensive chemicals of Calotropis before feeding
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