Exocrine glands, defensive secretion

If many unpalatable Lepidoptera obtain their defensive quality by sequestering plant-derived substances, various caterpillars fortify their bodies with spines and hairs containing various toxins [167]. Defensive secretions in specialized exocrine glands were also reported [150-152]. 

The exocrine glands of the caddisfly Pycnopsyche scabripennis (Lim-nephilidae) secrete a defensive exudate which contains indole (138) and skatole (140) along with p-cresol (Table VIII). This secretion effectively repels invertebrate predators such as ants. 

Quennedey, A. (1975). Morphology of exocrine glands producing pheromones and defensive substances in subsocial and social insects. In Pheromones and defensive secretions in social insects. Dijon Proceedings of the IUSSI, pp. 1-21. 

Oreina leaf beetles (Chrysomelidae, Coleoptera) synthesize cardenolides as part of their defensive secretions that are released from specialized exocrine glands.139,140 Some Oreina beetles sequester and secrete PAs, which are taken directly as N-oxides from their Asteraceae food plants.59 It is assumed that PA acquisition evolved in species that already possessed the ability to synthesize and store cardenolides for efficient defense.14 O. cacaliae is the only species in this family that lost the ability to synthesize cardenolides autogenously. Instead the plant-derived PA A-oxides are stored in the body (primarily in the hemolymph) and... 

Arthropods synthesize an incredible diversity of natural products in their exocrine glands (3) which are utilized with great effectiveness to blunt the attacks of their adversaries. The defensive secretions of these invertebrates can often be delivered with great accuracy, thus ensuring that aggressive predators are subjected to the full impact of these secretory effronteries (A). Significantly, these exudates usually manifest their defensive efficacy as effective repellents and thus constitute the first line of defense of the prey species. The deterrent value of the natural products in these secretions is inestimable, since it can permit their producers to escape predators without injurious physical confrontations. This is especially important in encounters with ants, since these social insects can quickly launch devastating en masse attacks. 

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