(Prepare yourselves. This post is about the sexiest paper that I have read in a long time.)
Many plants are covered in tiny hairs, called trichomes, which defend the plant by trapping insects. These can be hooked trichomes that snag insects, or glandular trichomes that produce secretions that the insects stick to. These trichomes may be beneficial because they trap and kill insects that might harm the plant. But they also seem somewhat detrimental, because predatory insects (e.g., lady beetles) that might benefit the plant by killing herbivorous insects (e.g., aphids) might also get stuck in the trichomes and die (Eisner et al. 1998).
However, some predatory arthropods can avoid getting stuck in the trichomes. For instance, the common tarweed has glandular trichomes, but it is still visited by five types of predatory arthropods (Krimmel and Pearse 2013). Interestingly, those predatory arthropods will eat both dead and living insect prey. AND GUESS WHAT?! Just like plants use extrafloral nectaries and food bodies to attract ant defenders, the dead insects trapped in the sticky trichomes of the tarweed attract those five predatory arthropods. Those predators reduce herbivory from a caterpillar by 60%, and that reduced herbivory leads to greater plant fitness. A. Maze. Ing. Go read the paper. It’s beautiful.
Fun facts from the paper:
20-30% of vascular plants have glandular trichomes. So, this specialized predator attraction may be a widespread phenomenon.
Individual plants had up to 40 insect corpses at a time!!
Eisner T, Eisner M, Hoebeke ER. 1998. When defense backfires: Detrimental effect of a plant’s protective trichomes on an insect beneficial to the plant. PNAS 95(8): 4410-4414.
Krimmel BA, Pearse IS. 2013. Sticky plant traps insects to enhance indirect defense. Ecology Letters 16: 219–224.