Insect Venom: Pain Laced with Promise

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    The forestry worker climbs a tree, seeking to gain a bird's-eye view over the surrounding forest. As he climbs from branch to branch, he notices a spiny caterpillar with striking coloration at eye level. Seeking to better examine the insect, he picks it up. Immediately, venom-filled spines along the caterpillar's length break off into his skin, injecting their toxic contents. A burst of pain shoots through the worker's hand, and he immediately drops the offending larva. Defensive venoms can be found in several insect groups. Though we generally associate venoms with pain, burning, intense itching, and other unpleasant sensations, new research into insect venoms provides hope for new treatments, pesticides, and other substances beneficial to the well-being of humanity.

Giant Silkworm caterpillar (Lepidoptera:Saturniidae) showing envenomated spines | Photo courtesy of Centro de Informações Toxicológicas de Santa Catarina and Wikipedia

    The biology and chemistry of insect venoms is a fascinating subject, full of both pain and promise which we have only begun to understand. For most people, the best known venomous insect groups are the bees and wasps, members of the order Hymenoptera. In all of these taxa, venom is produced in venom glands and administered through a highly modified ovipositor (Guido-Patiño and Plisson, 2022). These natural equivalents of needles are great at their job. They can be pushed through tissue easily, with as much as 1000 times less force than some of the smallest human needles (Zhou et al., 2015). However, though their origin, function, and basic structure are similar, sting mechanics differ within Hymenoptera.  Vespid stings (family Vespidae, social wasps) tend to be curved with minimal barbing along the lancet (see image below). This allows wasps to easily remove their stinger and reinsert it. As a result, they can sting a threatening vertebrate several times in different locations, injecting an average of 17 micrograms of pain-inducing venom per sting (Zhou et al., 2015).

Paper Wasp Stinger | Photo courtesy of Zhou et al., 2015

    In contrast, Bees (family Apidae) sport stingers with prominent barbs along their length which make them very difficult to remove from fibrous or fleshy materials. Because of these barbs, bees cannot sting more than once, as their venom glands and portions of their viscera are pulled out by the embedded stinger. The bee's one-and-done approach also means that they deliver venom in higher doses than wasps. The average amount of venom injected by a bee in a single sting is 174 micrograms, over ten times the average for vespids (Zhou et al., 2015). Both bee and wasp stings have immediate and painful effects due to the mixture of melittins, acuelatoxins, gamma-hexatoxins, and various other chemicals and proteins present in their venom (Guido-Patiño and Plisson, 2022). Symptoms after a sting include pain, swelling, and redness in most cases, but those with allergies to venom components (especially phospholipase A2 and melittin) and those who have been stung many times may experience severe respiratory system responses (Ewan, 1998). 

Barbed stinger of a Honey Bee (Hymenoptera: Apidae) | Photo courtesy of Zhou et al., 2015


    Though Hymenopteran venom is the most well-known, some members of the order Lepidoptera pack potent defensive venoms during larval stages. This is especially common in tropical species within  Saturniidae (Giant Silkmoths). In venomous species, caterpillars are covered in hollow, barbed spines or setae filled with a toxic mixture of proteins in solution. These structures are easily pulled off and broken open, so physical contact with a caterpillar results in injection within the skin. Some species have even evolved the ability to release their spines into the air without physical contact, creating a floating cloud of venom-filled spines (Seldeslachts, Peigneur, and Tytgat, 2020). Typical encounters with a venomous caterpillar result in redness, swelling, pain, and intense itch but are generally localized. However, in cases where a person is exposed to the venom of many caterpillars or many airborne setae, systemic reactions may result, which can be fatal in severe cases (Seldeslachts, Peigneur, and Tytgat, 2020).

Diagram of modified setae and spines in venomous caterpillars | Photo courtesy of Seldeslachts, Peigneur, and Tytgat, 2020


    Though insect venoms are meant to cause pain, immobilize prey, and/or deter predators, many of their proteins (especially those of bees and wasps) are under investigation for potential medicinal and agricultural applications. Many hymenopteran venoms possess anti-microbial properties and are being investigated as sources for new antibiotics. Other proteins possess potential anti-diabetic and anti-cancer properties that could be used to develop new treatments for these conditions (Guido-Patiño and Plisson, 2022). Many hymenopteran venoms also contain proteins with potent insecticidal properties and are being researched as models for new pesticides (Guido-Patiño and Plisson, 2022). Though few of the bioactive proteins are specific to a particular target insect, they could provide universal insecticides to which pests are not yet immune. 

    








Works Cited

Ewan P. W. (1998). Venom allergy. BMJ (Clinical research ed.), 316(7141), 1365–1368. https://doi.org/10.1136/bmj.316.7141.1365

Guido-Patiño, J. C., & Plisson, F. (2022). Profiling hymenopteran venom toxins: Protein families, structural landscape, biological activities, and pharmacological benefits. Toxicon: X, 14, 100119.             https://doi.org/10.1016/j.toxcx.2022.100119

Seldeslachts, A., Peigneur, S., & Tytgat, J. (2020). Caterpillar Venom: A Health Hazard of the 21st Century. Biomedicines, 8(6), 143. https://doi.org/10.3390/biomedicines8060143

Zhao, Z. L., Zhao, H. P., Ma, G. J., Wu, C. W., Yang, K., & Feng, X. Q. (2015). Structures, properties, and functions of the stings of honey bees and paper wasps: a comparative study. Biology open, 4(7), 921–928. https://doi.org/10.1242/bio.012195


Image Links

Giant Silkworm Caterpillar: 

https://en.wikipedia.org/wiki/Lonomia_obliqua#/media/File:Lonomia-obliqua-citsc-1.jpg

Honey Bee Stinger:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4571097/figure/BIO012195F3/

Paper Wasp Stinger:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4571097/figure/BIO012195F4/

Setae/Spine Diagram:

https://www.ncbi.nlm.nih.gov/core/lw/2.0/html/tileshop_pmc/tileshop_pmc_inline.html?                      title=Click%20on%20image%20to%20zoom&p=PMC3&id=7345192_biomedicines-08-00143-           g002.jpg



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